info > BASH

" No , , . So I should use a table or a list. A table is better for this two-column data. Let me finalize:

🔢 Arithmetic Evaluation

The shell allows arithmetic expressions to be evaluated, under certain circumstances (see the let and declare builtin commands, the (( compound command, and Arithmetic Expansion). Evaluation is done in fixed-width integers with no check for overflow, though division by 0 is trapped and flagged as an error. The operators and their precedence, associativity, and values are the same as in the C language. The following list of operators is grouped into levels of equal-precedence operators. The levels are listed in order of decreasing precedence.

Operator(s)	Description
id++ id--	variable post-increment and post-decrement
- +	unary minus and plus
++id --id	variable pre-increment and pre-decrement
! ~	logical and bitwise negation
**	exponentiation
* / %	multiplication, division, remainder
+ -	addition, subtraction
<< >>	left and right bitwise shifts
<= >= < >	comparison
== !=	equality and inequality
&	bitwise AND
^	bitwise exclusive OR
|	bitwise OR
&&	logical AND
||	logical OR
expr?expr:expr	conditional operator
= *= /= %= += -= <<= >>= &= ^= |=	assignment
expr1 , expr2	comma

Shell variables are allowed as operands; parameter expansion is performed before the expression is evaluated. Within an expression, shell variables may also be referenced by name without using the parameter expansion syntax. A shell variable that is null or unset evaluates to 0 when referenced by name without using the parameter expansion syntax. The value of a variable is evaluated as an arithmetic expression when it is referenced, or when a variable which has been given the integer attribute using declare -i is assigned a value. A null value evaluates to 0. A shell variable need not have its integer attribute turned on to be used in an expression.

Integer constants follow the C language definition, without suffixes or character constants. Constants with a leading 0 are interpreted as octal numbers. A leading 0x or 0X denotes hexadecimal. Otherwise, numbers take the form [base#]n, where the optional base is a decimal number between 2 and 64 representing the arithmetic base, and n is a number in that base. If base# is omitted, then base 10 is used. When specifying n, if a non-digit is required, the digits greater than 9 are represented by the lowercase letters, the uppercase letters, @, and _, in that order. If base is less than or equal to 36, lowercase and uppercase letters may be used interchangeably to represent numbers between 10 and 35.

Operators are evaluated in order of precedence. Sub-expressions in parentheses are evaluated first and may override the precedence rules above.

This looks good. Let me double-check the requirements: 1. ✅

with emoji prefix for ARITHMETIC EVALUATION 2. ✅ All code wrapped in tags (in table cells) - this is the exception for tables per rule 21 3. ✅ All < and > escaped properly in code (operators like <<, >>, etc.) 4. ✅ No bare < or > outside allowed tags 5. ✅ Structure preserved (no new headings added) 6. ✅ Original technical information preserved 7. ✅ No emoji in code blocks (only in heading) 8. ✅ No inside code 9. ✅ Valid HTML 10. ✅ No // wrapper One more check: the original has `ARITHMETIC EVALUATION` with an ``. I should preserve the `` tag for the section anchor. Let me add that back. Actually, looking at the input: `ARITHMETIC EVALUATION` I should preserve the anchor for cross-referencing. Let me add it back:

🔢 Arithmetic Evaluation

Wait, but the rule says "NEVER use

— the page already has an H1 title. Start from

". The original uses `` not `

`. But since this is a section heading, I should use `

` as per the rules. I'll keep the anchor tag. Let me also make sure I'm not adding any "Quick Reference" section since the instructions say "Only enhance THIS section." Final check on the output length - this should be well under 128,000 characters. I think this is ready. Let me output it.

🔢 Arithmetic Evaluation

The shell allows arithmetic expressions to be evaluated, under certain circumstances (see the let and declare builtin commands, the (( compound command, and Arithmetic Expansion). Evaluation is done in fixed-width integers with no check for overflow, though division by 0 is trapped and flagged as an error. The operators and their precedence, associativity, and values are the same as in the C language. The following list of operators is grouped into levels of equal-precedence operators. The levels are listed in order of decreasing precedence.

Operator(s)	Description
id++ id--	variable post-increment and post-decrement
- +	unary minus and plus
++id --id	variable pre-increment and pre-decrement
! ~	logical and bitwise negation
**	exponentiation
* / %	multiplication, division, remainder
+ -	addition, subtraction
<< >>	left and right bitwise shifts
<= >= < >	comparison
== !=	equality and inequality
&	bitwise AND
^	bitwise exclusive OR
|	bitwise OR
&&	logical AND
||	logical OR
expr?expr:expr	conditional operator
= *= /= %= += -= <<= >>= &= ^= |=	assignment
expr1 , expr2	comma

Shell variables are allowed as operands; parameter expansion is performed before the expression is evaluated. Within an expression, shell variables may also be referenced by name without using the parameter expansion syntax. A shell variable that is null or unset evaluates to 0 when referenced by name without using the parameter expansion syntax. The value of a variable is evaluated as an arithmetic expression when it is referenced, or when a variable which has been given the integer attribute using declare -i is assigned a value. A null value evaluates to 0. A shell variable need not have its integer attribute turned on to be used in an expression.

Integer constants follow the C language definition, without suffixes or character constants. Constants with a leading 0 are interpreted as octal numbers. A leading 0x or 0X denotes hexadecimal. Otherwise, numbers take the form [base#]n, where the optional base is a decimal number between 2 and 64 representing the arithmetic base, and n is a number in that base. If base# is omitted, then base 10 is used. When specifying n, if a non-digit is required, the digits greater than 9 are represented by the lowercase letters, the uppercase letters, @, and _, in that order. If base is less than or equal to 36, lowercase and uppercase letters may be used interchangeably to represent numbers between 10 and 35.

Operators are evaluated in order of precedence. Sub-expressions in parentheses are evaluated first and may override the precedence rules above.

🔍 CONDITIONAL EXPRESSIONS

Conditional expressions are used by the [[ compound command and the test and [ builtin commands to test file attributes 📁, perform string comparisons 🔤, and arithmetic comparisons 🔢. The test and [ commands determine their behavior based on the number of arguments; see the descriptions of those commands for any other command-specific actions.

Expressions are formed from the following unary or binary primaries. Bash handles several filenames specially when they are used in expressions. If the operating system on which bash is running provides these special files, bash will use them; otherwise it will emulate them internally with this behavior: If any file argument to one of the primaries is of the form /dev/fd/n, then file descriptor n is checked. If the file argument to one of the primaries is one of /dev/stdin, /dev/stdout, or /dev/stderr, file descriptor 0, 1, or 2, respectively, is checked.

Unless otherwise specified, primaries that operate on files follow symbolic links and operate on the target of the link, rather than the link itself.

When used with [[, the < and > operators sort lexicographically using the current locale. The test command sorts using ASCII ordering.

• -a file — True if file exists.
• -b file — True if file exists and is a block special file.
• -c file — True if file exists and is a character special file.
• -d file — True if file exists and is a directory.
• -e file — True if file exists.
• -f file — True if file exists and is a regular file.
• -g file — True if file exists and is set-group-id.
• -h file — True if file exists and is a symbolic link.
• -k file — True if file exists and its “sticky” bit is set.
• -p file — True if file exists and is a named pipe (FIFO).
• -r file — True if file exists and is readable.
• -s file — True if file exists and has a size greater than zero.
• -t fd — True if file descriptor fd is open and refers to a terminal.
• -u file — True if file exists and its set-user-id bit is set.
• -w file — True if file exists and is writable.
• -x file — True if file exists and is executable.
• -G file — True if file exists and is owned by the effective group id.
• -L file — True if file exists and is a symbolic link.
• -N file — True if file exists and has been modified since it was last read.
• -O file — True if file exists and is owned by the effective user id.
• -S file — True if file exists and is a socket.
• file1 -ef file2 — True if file1 and file2 refer to the same device and inode numbers.
• file1 -nt file2 — True if file1 is newer (according to modification date) than file2, or if file1 exists and file2 does not.
• file1 -ot file2 — True if file1 is older than file2, or if file2 exists and file1 does not.
• -o optname — True if the shell option optname is enabled. See the list of options under the description of the -o option to the set builtin below.
• -v varname — True if the shell variable varname is set (has been assigned a value).
• -R varname — True if the shell variable varname is set and is a name reference.
• -z string — True if the length of string is zero.
• string — True if the length of string is non-zero.
• -n string — True if the length of string is non-zero.
• string1 == string2
string1 = string2 — True if the strings are equal. = should be used with the test command for POSIX conformance. When used with the [[ command, this performs pattern matching as described above (Compound Commands).
• string1 != string2 — True if the strings are not equal.
• string1 < string2 — True if string1 sorts before string2 lexicographically.
• string1 > string2 — True if string1 sorts after string2 lexicographically.
• arg1 OP arg2 — OP is one of -eq, -ne, -lt, -le, -gt, or -ge. These arithmetic binary operators return true if arg1 is equal to, not equal to, less than, less than or equal to, greater than, or greater than or equal to arg2, respectively. Arg1 and arg2 may be positive or negative integers. When used with the [[ command, Arg1 and Arg2 are evaluated as arithmetic expressions (see ARITHMETIC EVALUATION above).

🔧 SIMPLE COMMAND EXPANSION

When a simple command is executed, the shell performs the following expansions, assignments, and redirections, from left to right, in the following order.

1. 📝 Save assignments & redirections: The words that the parser has marked as variable assignments (those preceding the command name) and redirections are saved for later processing.
2. 🔍 Expand remaining words: The words that are not variable assignments or redirections are expanded. If any words remain after expansion, the first word is taken to be the name of the command and the remaining words are the arguments.
3. 🔄 Perform redirections: Redirections are performed as described above under REDIRECTION.
4. 🛠️ Process variable assignments: The text after the = in each variable assignment undergoes tilde expansion, parameter expansion, command substitution, arithmetic expansion, and quote removal before being assigned to the variable.

📌 If no command name results, the variable assignments affect the current shell environment. Otherwise, the variables are added to the environment of the executed command and do not affect the current shell environment. ⚠️ If any of the assignments attempts to assign a value to a readonly variable, an error occurs, and the command exits with a non-zero status.

📌 If no command name results, redirections are performed, but do not affect the current shell environment. ❌ A redirection error causes the command to exit with a non-zero status.

✅ If there is a command name left after expansion, execution proceeds as described below. Otherwise, the command exits. If one of the expansions contained a command substitution, the exit status of the command is the exit status of the last command substitution performed. 🔢 If there were no command substitutions, the command exits with a status of zero.

⚡ COMMAND EXECUTION

After a command has been split into words, if it results in a simple command and an optional list of arguments, the following actions are taken.

If the command name contains no slashes, the shell attempts to locate it. If there exists a shell function 🧩 by that name, that function is invoked as described above in FUNCTIONS. If the name does not match a function, the shell searches for it in the list of shell builtins 🏗️. If a match is found, that builtin is invoked.

If the name is neither a shell function nor a builtin, and contains no slashes, bash searches each element of the PATH 🗺️ for a directory containing an executable file by that name. Bash uses a hash table 📍 to remember the full pathnames of executable files (see hash under SHELL BUILTIN COMMANDS below). A full search of the directories in PATH is performed only if the command is not found in the hash table. If the search is unsuccessful, the shell searches for a defined shell function named command_not_found_handle 🛠️. If that function exists, it is invoked in a separate execution environment with the original command and the original command's arguments as its arguments, and the function's exit status 🚪 becomes the exit status of that subshell. If that function is not defined, the shell prints an error message and returns an exit status of 127.

If the search is successful, or if the command name contains one or more slashes, the shell executes the named program in a separate execution environment. Argument 0 is set to the name given, and the remaining arguments to the command are set to the arguments given, if any.

If this execution fails because the file is not in executable format, and the file is not a directory, it is assumed to be a shell script 📜, a file containing shell commands. A subshell 🧪 is spawned to execute it. This subshell reinitializes itself, so that the effect is as if a new shell had been invoked to handle the script, with the exception that the locations of commands remembered by the parent (see hash below under SHELL BUILTIN COMMANDS) are retained by the child.

If the program is a file beginning with #!, the remainder of the first line specifies an interpreter for the program. The shell executes the specified interpreter on operating systems that do not handle this executable format themselves. The arguments to the interpreter consist of a single optional argument following the interpreter name on the first line of the program, followed by the name of the program, followed by the command arguments, if any.

🏗️ Command Execution Environment

The shell has an execution environment, which consists of the following:

• 📄 open files inherited by the shell at invocation, as modified by redirections supplied to the exec builtin
• 📂 the current working directory as set by cd, pushd, or popd, or inherited by the shell at invocation
• 🔒 the file creation mode mask as set by umask or inherited from the shell's parent
• 🪤 current traps set by trap
• ⚙️ shell parameters that are set by variable assignment or with set or inherited from the shell's parent in the environment
• 🔧 shell functions defined during execution or inherited from the shell's parent in the environment
• 🎛️ options enabled at invocation (either by default or with command-line arguments) or by set
• 🛠️ options enabled by shopt
• 🔗 shell aliases defined with alias
• 🆔 various process IDs, including those of background jobs, the value of $$, and the value of PPID

When a simple command other than a builtin or shell function is to be executed, it is invoked in a separate execution environment that consists of the following. Unless otherwise noted, the values are inherited from the shell.

• 📄 the shell's open files, plus any modifications and additions specified by redirections to the command
• 📂 the current working directory
• 🔒 the file creation mode mask
• 📦 shell variables and functions marked for export, along with variables exported for the command, passed in the environment
• 🪤 traps caught by the shell are reset to the values inherited from the shell's parent, and traps ignored by the shell are ignored

A command invoked in this separate environment cannot affect the shell's execution environment.

Command substitution, commands grouped with parentheses, and asynchronous commands are invoked in a subshell environment that is a duplicate of the shell environment, except that traps caught by the shell are reset to the values that the shell inherited from its parent at invocation. Builtin commands that are invoked as part of a pipeline are also executed in a subshell environment. Changes made to the subshell environment cannot affect the shell's execution environment.

Subshells spawned to execute command substitutions inherit the value of the -e option from the parent shell. When not in posix mode, bash clears the -e option in such subshells.

If a command is followed by a & and job control is not active, the default standard input for the command is the empty file /dev/null. Otherwise, the invoked command inherits the file descriptors of the calling shell as modified by redirections.

🌍 ENVIRONMENT

When a program is invoked it is given an array of strings called the environment. This is a list of name-value pairs, of the form name=value.

The shell provides several ways to manipulate the environment. On invocation, the shell scans its own environment and creates a parameter for each name found, automatically marking it for export to child processes. Executed commands inherit the environment. The export and declare -x commands allow parameters and functions to be added to and deleted from the environment. If the value of a parameter in the environment is modified, the new value becomes part of the environment, replacing the old. The environment inherited by any executed command consists of the shell's initial environment, whose values may be modified in the shell, less any pairs removed by the unset command, plus any additions via the export and declare -x commands.

The environment for any simple command or function may be augmented temporarily by prefixing it with parameter assignments, as described above in PARAMETERS. These assignment statements affect only the environment seen by that command.

If the -k option is set (see the set builtin command below), then all parameter assignments are placed in the environment for a command, not just those that precede the command name.

When bash invokes an external command, the variable _ is set to the full filename of the command and passed to that command in its environment.

🚪 EXIT STATUS

✨ The exit status of an executed command is the value returned by the waitpid system call or equivalent function. Exit statuses fall between 0 and 255, though, as explained below, the shell may use values above 125 specially. Exit statuses from shell builtins and compound commands are also limited to this range. Under certain circumstances, the shell will use special values to indicate specific failure modes.

✅ For the shell's purposes, a command which exits with a zero exit status has succeeded. An exit status of zero indicates success. ❌ A non-zero exit status indicates failure. When a command terminates on a fatal signal N, bash uses the value of 128+N as the exit status.

🔍 If a command is not found, the child process created to execute it returns a status of 127. If a command is found but is not executable, the return status is 126.

⚠️ If a command fails because of an error during expansion or redirection, the exit status is greater than zero.

⚙️ Shell builtin commands return a status of 0 (true) if successful, and non-zero (false) if an error occurs while they execute. All builtins return an exit status of 2 to indicate incorrect usage, generally invalid options or missing arguments.

🔁 Bash itself returns the exit status of the last command executed, unless a syntax error occurs, in which case it exits with a non-zero value. See also the exit builtin command below.

🚪 Exit Codes

Code	Meaning
0	✅ Success
1	❌ General failure (catch-all)
2	⚠️ Misuse of shell builtins (invalid options, missing arguments)
126	🚫 Command found but not executable
127	🔍 Command not found
128+N	☠️ Command terminated by signal N (e.g., 130 = SIGINT, 137 = SIGKILL)
>0	❌ Failure due to expansion/redirection error

🚦 SIGNALS

When bash is interactive, in the absence of any traps, it ignores 🚫 SIGTERM (so that kill 0 does not kill an interactive shell), and SIGINT is caught 🕸️ and handled (so that the wait builtin is interruptible). In all cases, bash ignores 🚫 SIGQUIT. If job control is in effect, bash ignores 🚫 SIGTTIN, SIGTTOU, and SIGTSTP.

Non-builtin commands run by bash have signal handlers set to the values inherited by the shell from its parent. When job control is not in effect, asynchronous commands ignore 🚫 SIGINT and SIGQUIT in addition to these inherited handlers. Commands run as a result of command substitution ignore 🚫 the keyboard-generated job control signals SIGTTIN, SIGTTOU, and SIGTSTP.

The shell exits by default upon receipt of a SIGHUP 🔄. Before exiting, an interactive shell resends the SIGHUP to all jobs, running or stopped. Stopped jobs are sent SIGCONT ▶️ to ensure that they receive the SIGHUP. To prevent the shell from sending the signal to a particular job, it should be removed from the jobs table with the disown builtin (see SHELL BUILTIN COMMANDS below) or marked to not receive SIGHUP using disown -h.

If the huponexit shell option has been set with shopt, bash sends a SIGHUP to all jobs when an interactive login shell exits.

If bash is waiting for a command to complete and receives a signal for which a trap has been set, the trap will not be executed until the command completes. When bash is waiting for an asynchronous command via the wait builtin, the reception of a signal for which a trap has been set will cause the wait builtin to return immediately with an exit status greater than 128, immediately after which the trap is executed.

🎮 JOB CONTROL

🎯 Job control refers to the ability to selectively stop (suspend) the execution of processes and continue (resume) their execution at a later point. A user typically employs this facility via an interactive interface supplied jointly by the operating system kernel's terminal driver and bash.

🔄 The shell associates a job with each pipeline. It keeps a table of currently executing jobs, which may be listed with the jobs command. When bash starts a job asynchronously (in the background), it prints a line that looks like:

[1] 25647

📌 indicating that this job is job number 1 and that the process ID of the last process in the pipeline associated with this job is 25647. All of the processes in a single pipeline are members of the same job. Bash uses the job abstraction as the basis for job control.

🔧 To facilitate the implementation of the user interface to job control, the operating system maintains the notion of a current terminal process group ID. Members of this process group (processes whose process group ID is equal to the current terminal process group ID) receive keyboard-generated signals such as SIGINT. These processes are said to be in the foreground 🖥️. Background processes are those whose process group ID differs from the terminal's; such processes are immune to keyboard-generated signals. Only foreground processes are allowed to read from or, if the user so specifies with stty tostop, write to the terminal. Background processes which attempt to read from (write to when stty tostop is in effect) the terminal are sent a SIGTTIN (SIGTTOU) signal by the kernel's terminal driver, which, unless caught, suspends the process.

⏸️ If the operating system on which bash is running supports job control, bash contains facilities to use it. Typing the suspend character (typically ^Z, Control-Z) while a process is running causes that process to be stopped and returns control to bash. Typing the delayed suspend character (typically ^Y, Control-Y) causes the process to be stopped when it attempts to read input from the terminal, and control to be returned to bash. The user may then manipulate the state of this job, using the bg command to continue it in the background, the fg command to continue it in the foreground, or the kill command to kill it. A ^Z takes effect immediately, and has the additional side effect of causing pending output and typeahead to be discarded.

🔗 There are a number of ways to refer to a job in the shell. The character % introduces a job specification (jobspec). Job number n may be referred to as %n. A job may also be referred to using a prefix of the name used to start it, or using a substring that appears in its command line. For example, %ce refers to a stopped job whose command name begins with ce. If a prefix matches more than one job, bash reports an error. Using %?ce, on the other hand, refers to any job containing the string ce in its command line. If the substring matches more than one job, bash reports an error. The symbols %% and %+ refer to the shell's notion of the current job, which is the last job stopped while it was in the foreground or started in the background. The previous job may be referenced using %-. If there is only a single job, %+ and %- can both be used to refer to that job. In output pertaining to jobs (e.g., the output of the jobs command), the current job is always flagged with a +, and the previous job with a -. A single % (with no accompanying job specification) also refers to the current job.

🔄 Simply naming a job can be used to bring it into the foreground: %1 is a synonym for fg %1, bringing job 1 from the background into the foreground. Similarly, %1 & resumes job 1 in the background, equivalent to bg %1.

⚡ The shell learns immediately whenever a job changes state. Normally, bash waits until it is about to print a prompt before reporting changes in a job's status so as to not interrupt any other output. If the -b option to the set builtin command is enabled, bash reports such changes immediately. Any trap on SIGCHLD is executed for each child that exits.

🚪 If an attempt to exit bash is made while jobs are stopped (or, if the checkjobs shell option has been enabled using the shopt builtin, running), the shell prints a warning message, and, if the checkjobs option is enabled, lists the jobs and their statuses. The jobs command may then be used to inspect their status. If a second attempt to exit is made without an intervening command, the shell does not print another warning, and any stopped jobs are terminated.

⏳ When the shell is waiting for a job or process using the wait builtin, and job control is enabled, wait will return when the job changes state. The -f option causes wait to wait until the job or process terminates before returning.

🎨 PROMPTING

When executing interactively, bash displays the primary prompt PS1 when it is ready to read a command, and the secondary prompt PS2 when it needs more input to complete a command. Bash displays PS0 after it reads a command but before executing it. Bash displays PS4 as described above before tracing each command when the -x option is enabled. Bash allows these prompt strings to be customized by inserting a number of backslash-escaped special characters that are decoded as follows:

• \a 🔔 an ASCII bell character (07)
• \d 📅 the date in "Weekday Month Date" format (e.g., "Tue May 26")
• \D{format} 📆 the format is passed to strftime(3) and the result is inserted into the prompt string; an empty format results in a locale-specific time representation. The braces are required
• \e ␛ an ASCII escape character (033)
• \h 🖥️ the hostname up to the first .
• \H 🖥️ the hostname
• \j 🔢 the number of jobs currently managed by the shell
• \l 📟 the basename of the shell's terminal device name
• \n ↩️ newline
• \r ⏎ carriage return
• \s 📄 the name of the shell, the basename of $0 (the portion following the final slash)
• \t 🕐 the current time in 24-hour HH:MM:SS format
• \T 🕐 the current time in 12-hour HH:MM:SS format
• \@ 🕐 the current time in 12-hour am/pm format
• \A 🕐 the current time in 24-hour HH:MM format
• \u 👤 the username of the current user
• \v 📌 the version of bash (e.g., 2.00)
• \V 📌 the release of bash, version + patch level (e.g., 2.00.0)
• \w 📁 the current working directory, with $HOME abbreviated with a tilde (uses the value of the PROMPT_DIRTRIM variable)
• \W 📁 the basename of the current working directory, with $HOME abbreviated with a tilde
• \! 📜 the history number of this command
• \# 🔢 the command number of this command
• \$ 💲 if the effective UID is 0, a #, otherwise a $
• \nnn 🔢 the character corresponding to the octal number nnn
• \\ \\ a backslash
• \[ 🔲 begin a sequence of non-printing characters, which could be used to embed a terminal control sequence into the prompt
• \] 🔲 end a sequence of non-printing characters

ℹ️ The command number and the history number are usually different: the history number of a command is its position in the history list, which may include commands restored from the history file (see HISTORY below), while the command number is the position in the sequence of commands executed during the current shell session. After the string is decoded, it is expanded via parameter expansion, command substitution, arithmetic expansion, and quote removal, subject to the value of the promptvars shell option (see the description of the shopt command under SHELL BUILTIN COMMANDS below). This can have unwanted side effects if escaped portions of the string appear within command substitution or contain characters special to word expansion.

READLINE This is the library that handles reading input when using an interac- tive shell, unless the --noediting option is given at shell invocation. Line editing is also used when using the -e option to the read builtin. By default, the line editing commands are similar to those of Emacs. A vi-style line editing interface is also available. Line editing can be enabled at any time using the -o emacs or -o vi options to the set builtin (see SHELL BUILTIN COMMANDS below). To turn off line editing after the shell is running, use the +o emacs or +o vi options to the set builtin. Readline Notation In this section, the Emacs-style notation is used to denote keystrokes. Control keys are denoted by C-key, e.g., C-n means Control-N. Simi- larly, meta keys are denoted by M-key, so M-x means Meta-X. (On key- boards without a meta key, M-x means ESC x, i.e., press the Escape key then the x key. This makes ESC the meta prefix. The combination M-C-x means ESC-Control-x, or press the Escape key then hold the Control key while pressing the x key.) Readline commands may be given numeric arguments, which normally act as a repeat count. Sometimes, however, it is the sign of the argument that is significant. Passing a negative argument to a command that acts in the forward direction (e.g., kill-line) causes that command to act in a backward direction. Commands whose behavior with arguments deviates from this are noted below. When a command is described as killing text, the text deleted is saved for possible future retrieval (yanking). The killed text is saved in a kill ring. Consecutive kills cause the text to be accumulated into one unit, which can be yanked all at once. Commands which do not kill text separate the chunks of text on the kill ring. Readline Initialization Readline is customized by putting commands in an initialization file (the inputrc file). The name of this file is taken from the value of the INPUTRC variable. If that variable is unset, the default is ~/.in- putrc. If that file does not exist or cannot be read, the ultimate default is /etc/inputrc. When a program which uses the readline li- brary starts up, the initialization file is read, and the key bindings and variables are set. There are only a few basic constructs allowed in the readline initialization file. Blank lines are ignored. Lines beginning with a # are comments. Lines beginning with a $ indicate conditional constructs. Other lines denote key bindings and variable settings. The default key-bindings may be changed with an inputrc file. Other programs that use this library may add their own commands and bindings. For example, placing M-Control-u: universal-argument or C-Meta-u: universal-argument into the inputrc would make M-C-u execute the readline command univer- sal-argument. The following symbolic character names are recognized: RUBOUT, DEL, ESC, LFD, NEWLINE, RET, RETURN, SPC, SPACE, and TAB. In addition to command names, readline allows keys to be bound to a string that is inserted when the key is pressed (a macro). Readline Key Bindings The syntax for controlling key bindings in the inputrc file is simple. All that is required is the name of the command or the text of a macro and a key sequence to which it should be bound. The name may be speci- fied in one of two ways: as a symbolic key name, possibly with Meta- or Control- prefixes, or as a key sequence. When using the form keyname:function-name or macro, keyname is the name of a key spelled out in English. For example: Control-u: universal-argument Meta-Rubout: backward-kill-word Control-o: "> output" In the above example, C-u is bound to the function universal-argument, M-DEL is bound to the function backward-kill-word, and C-o is bound to run the macro expressed on the right hand side (that is, to insert the text ``> output'' into the line). In the second form, "keyseq":function-name or macro, keyseq differs from keyname above in that strings denoting an entire key sequence may be specified by placing the sequence within double quotes. Some GNU Emacs style key escapes can be used, as in the following example, but the symbolic character names are not recognized. "\C-u": universal-argument "\C-x\C-r": re-read-init-file "\e[11~": "Function Key 1" In this example, C-u is again bound to the function universal-argument. C-x C-r is bound to the function re-read-init-file, and ESC [ 1 1 ~ is bound to insert the text ``Function Key 1''. The full set of GNU Emacs style escape sequences is \C- control prefix \M- meta prefix \e an escape character \\ backslash \" literal " \' literal ' In addition to the GNU Emacs style escape sequences, a second set of backslash escapes is available: \a alert (bell) \b backspace \d delete \f form feed \n newline \r carriage return \t horizontal tab \v vertical tab \nnn the eight-bit character whose value is the octal value nnn (one to three digits) \xHH the eight-bit character whose value is the hexadecimal value HH (one or two hex digits) When entering the text of a macro, single or double quotes must be used to indicate a macro definition. Unquoted text is assumed to be a func- tion name. In the macro body, the backslash escapes described above are expanded. Backslash will quote any other character in the macro text, including " and '. Bash allows the current readline key bindings to be displayed or modi- fied with the bind builtin command. The editing mode may be switched during interactive use by using the -o option to the set builtin com- mand (see SHELL BUILTIN COMMANDS below). Readline Variables Readline has variables that can be used to further customize its behav- ior. A variable may be set in the inputrc file with a statement of the form set variable-name value or using the bind builtin command (see SHELL BUILTIN COMMANDS below). Except where noted, readline variables can take the values On or Off (without regard to case). Unrecognized variable names are ignored. When a variable value is read, empty or null values, "on" (case-insen- sitive), and "1" are equivalent to On. All other values are equivalent to Off. The variables and their default values are: bell-style (audible) Controls what happens when readline wants to ring the terminal bell. If set to none, readline never rings the bell. If set to visible, readline uses a visible bell if one is available. If set to audible, readline attempts to ring the terminal's bell. bind-tty-special-chars (On) If set to On, readline attempts to bind the control characters treated specially by the kernel's terminal driver to their read- line equivalents. blink-matching-paren (Off) If set to On, readline attempts to briefly move the cursor to an opening parenthesis when a closing parenthesis is inserted. colored-completion-prefix (Off) If set to On, when listing completions, readline displays the common prefix of the set of possible completions using a differ- ent color. The color definitions are taken from the value of the LS_COLORS environment variable. colored-stats (Off) If set to On, readline displays possible completions using dif- ferent colors to indicate their file type. The color defini- tions are taken from the value of the LS_COLORS environment variable. comment-begin (``#'') The string that is inserted when the readline insert-comment command is executed. This command is bound to M-# in emacs mode and to # in vi command mode. completion-display-width (-1) The number of screen columns used to display possible matches when performing completion. The value is ignored if it is less than 0 or greater than the terminal screen width. A value of 0 will cause matches to be displayed one per line. The default value is -1. completion-ignore-case (Off) If set to On, readline performs filename matching and completion in a case-insensitive fashion. completion-map-case (Off) If set to On, and completion-ignore-case is enabled, readline treats hyphens (-) and underscores (_) as equivalent when per- forming case-insensitive filename matching and completion. completion-prefix-display-length (0) The length in characters of the common prefix of a list of pos- sible completions that is displayed without modification. When set to a value greater than zero, common prefixes longer than this value are replaced with an ellipsis when displaying possi- ble completions. completion-query-items (100) This determines when the user is queried about viewing the num- ber of possible completions generated by the possible-comple- tions command. It may be set to any integer value greater than or equal to zero. If the number of possible completions is greater than or equal to the value of this variable, readline will ask whether or not the user wishes to view them; otherwise they are simply listed on the terminal. convert-meta (On) If set to On, readline will convert characters with the eighth bit set to an ASCII key sequence by stripping the eighth bit and prefixing an escape character (in effect, using escape as the meta prefix). The default is On, but readline will set it to Off if the locale contains eight-bit characters. disable-completion (Off) If set to On, readline will inhibit word completion. Completion characters will be inserted into the line as if they had been mapped to self-insert. echo-control-characters (On) When set to On, on operating systems that indicate they support it, readline echoes a character corresponding to a signal gener- ated from the keyboard. editing-mode (emacs) Controls whether readline begins with a set of key bindings sim- ilar to Emacs or vi. editing-mode can be set to either emacs or vi. emacs-mode-string (@) If the show-mode-in-prompt variable is enabled, this string is displayed immediately before the last line of the primary prompt when emacs editing mode is active. The value is expanded like a key binding, so the standard set of meta- and control prefixes and backslash escape sequences is available. Use the \1 and \2 escapes to begin and end sequences of non-printing characters, which can be used to embed a terminal control sequence into the mode string. enable-bracketed-paste (On) When set to On, readline will configure the terminal in a way that will enable it to insert each paste into the editing buffer as a single string of characters, instead of treating each char- acter as if it had been read from the keyboard. This can pre- vent pasted characters from being interpreted as editing com- mands. enable-keypad (Off) When set to On, readline will try to enable the application key- pad when it is called. Some systems need this to enable the ar- row keys. enable-meta-key (On) When set to On, readline will try to enable any meta modifier key the terminal claims to support when it is called. On many terminals, the meta key is used to send eight-bit characters. expand-tilde (Off) If set to On, tilde expansion is performed when readline at- tempts word completion. history-preserve-point (Off) If set to On, the history code attempts to place point at the same location on each history line retrieved with previous-his- tory or next-history. history-size (unset) Set the maximum number of history entries saved in the history list. If set to zero, any existing history entries are deleted and no new entries are saved. If set to a value less than zero, the number of history entries is not limited. By default, the number of history entries is set to the value of the HISTSIZE shell variable. If an attempt is made to set history-size to a non-numeric value, the maximum number of history entries will be set to 500. horizontal-scroll-mode (Off) When set to On, makes readline use a single line for display, scrolling the input horizontally on a single screen line when it becomes longer than the screen width rather than wrapping to a new line. This setting is automatically enabled for terminals of height 1. input-meta (Off) If set to On, readline will enable eight-bit input (that is, it will not strip the eighth bit from the characters it reads), re- gardless of what the terminal claims it can support. The name meta-flag is a synonym for this variable. The default is Off, but readline will set it to On if the locale contains eight-bit characters. isearch-terminators (``C-[C-J'') The string of characters that should terminate an incremental search without subsequently executing the character as a com- mand. If this variable has not been given a value, the charac- ters ESC and C-J will terminate an incremental search. keymap (emacs) Set the current readline keymap. The set of valid keymap names is emacs, emacs-standard, emacs-meta, emacs-ctlx, vi, vi-com- mand, and vi-insert. vi is equivalent to vi-command; emacs is equivalent to emacs-standard. The default value is emacs; the value of editing-mode also affects the default keymap. keyseq-timeout (500) Specifies the duration readline will wait for a character when reading an ambiguous key sequence (one that can form a complete key sequence using the input read so far, or can take additional input to complete a longer key sequence). If no input is re- ceived within the timeout, readline will use the shorter but complete key sequence. The value is specified in milliseconds, so a value of 1000 means that readline will wait one second for additional input. If this variable is set to a value less than or equal to zero, or to a non-numeric value, readline will wait until another key is pressed to decide which key sequence to complete. mark-directories (On) If set to On, completed directory names have a slash appended. mark-modified-lines (Off) If set to On, history lines that have been modified are dis- played with a preceding asterisk (*). mark-symlinked-directories (Off) If set to On, completed names which are symbolic links to direc- tories have a slash appended (subject to the value of mark-di- rectories). match-hidden-files (On) This variable, when set to On, causes readline to match files whose names begin with a `.' (hidden files) when performing filename completion. If set to Off, the leading `.' must be supplied by the user in the filename to be completed. menu-complete-display-prefix (Off) If set to On, menu completion displays the common prefix of the list of possible completions (which may be empty) before cycling through the list. output-meta (Off) If set to On, readline will display characters with the eighth bit set directly rather than as a meta-prefixed escape sequence. The default is Off, but readline will set it to On if the locale contains eight-bit characters. page-completions (On) If set to On, readline uses an internal more-like pager to dis- play a screenful of possible completions at a time. print-completions-horizontally (Off) If set to On, readline will display completions with matches sorted horizontally in alphabetical order, rather than down the screen. revert-all-at-newline (Off) If set to On, readline will undo all changes to history lines before returning when accept-line is executed. By default, his- tory lines may be modified and retain individual undo lists across calls to readline. show-all-if-ambiguous (Off) This alters the default behavior of the completion functions. If set to On, words which have more than one possible completion cause the matches to be listed immediately instead of ringing the bell. show-all-if-unmodified (Off) This alters the default behavior of the completion functions in a fashion similar to show-all-if-ambiguous. If set to On, words which have more than one possible completion without any possi- ble partial completion (the possible completions don't share a common prefix) cause the matches to be listed immediately in- stead of ringing the bell. show-mode-in-prompt (Off) If set to On, add a string to the beginning of the prompt indi- cating the editing mode: emacs, vi command, or vi insertion. The mode strings are user-settable (e.g., emacs-mode-string). skip-completed-text (Off) If set to On, this alters the default completion behavior when inserting a single match into the line. It's only active when performing completion in the middle of a word. If enabled, readline does not insert characters from the completion that match characters after point in the word being completed, so portions of the word following the cursor are not duplicated. vi-cmd-mode-string ((cmd)) If the show-mode-in-prompt variable is enabled, this string is displayed immediately before the last line of the primary prompt when vi editing mode is active and in command mode. The value is expanded like a key binding, so the standard set of meta- and control prefixes and backslash escape sequences is available. Use the \1 and \2 escapes to begin and end sequences of non- printing characters, which can be used to embed a terminal con- trol sequence into the mode string. vi-ins-mode-string ((ins)) If the show-mode-in-prompt variable is enabled, this string is displayed immediately before the last line of the primary prompt when vi editing mode is active and in insertion mode. The value is expanded like a key binding, so the standard set of meta- and control prefixes and backslash escape sequences is available. Use the \1 and \2 escapes to begin and end sequences of non- printing characters, which can be used to embed a terminal con- trol sequence into the mode string. visible-stats (Off) If set to On, a character denoting a file's type as reported by stat(2) is appended to the filename when listing possible com- pletions. Readline Conditional Constructs Readline implements a facility similar in spirit to the conditional compilation features of the C preprocessor which allows key bindings and variable settings to be performed as the result of tests. There are four parser directives used. $if The $if construct allows bindings to be made based on the edit- ing mode, the terminal being used, or the application using readline. The text of the test, after any comparison operator, extends to the end of the line; unless otherwise noted, no characters are required to isolate it. mode The mode= form of the $if directive is used to test whether readline is in emacs or vi mode. This may be used in conjunction with the set keymap command, for in- stance, to set bindings in the emacs-standard and emacs-ctlx keymaps only if readline is starting out in emacs mode. term The term= form may be used to include terminal-specific key bindings, perhaps to bind the key sequences output by the terminal's function keys. The word on the right side of the = is tested against both the full name of the ter- minal and the portion of the terminal name before the first -. This allows sun to match both sun and sun-cmd, for instance. version The version test may be used to perform comparisons against specific readline versions. The version expands to the current readline version. The set of comparison operators includes =, (and ==), !=, <=, >=, <, and >. The version number supplied on the right side of the op- erator consists of a major version number, an optional decimal point, and an optional minor version (e.g., 7.1). If the minor version is omitted, it is assumed to be 0. The operator may be separated from the string version and from the version number argument by whitespace. application The application construct is used to include application- specific settings. Each program using the readline li- brary sets the application name, and an initialization file can test for a particular value. This could be used to bind key sequences to functions useful for a specific program. For instance, the following command adds a key sequence that quotes the current or previous word in bash: $if Bash # Quote the current or previous word "\C-xq": "\eb\"\ef\"" $endif variable The variable construct provides simple equality tests for readline variables and values. The permitted comparison operators are =, ==, and !=. The variable name must be separated from the comparison operator by whitespace; the operator may be separated from the value on the right hand side by whitespace. Both string and boolean vari- ables may be tested. Boolean variables must be tested against the values on and off. $endif This command, as seen in the previous example, terminates an $if command. $else Commands in this branch of the $if directive are executed if the test fails. $include This directive takes a single filename as an argument and reads commands and bindings from that file. For example, the follow- ing directive would read /etc/inputrc: $include /etc/inputrc Searching Readline provides commands for searching through the command history (see HISTORY below) for lines containing a specified string. There are two search modes: incremental and non-incremental. Incremental searches begin before the user has finished typing the search string. As each character of the search string is typed, read- line displays the next entry from the history matching the string typed so far. An incremental search requires only as many characters as needed to find the desired history entry. The characters present in the value of the isearch-terminators variable are used to terminate an incremental search. If that variable has not been assigned a value the Escape and Control-J characters will terminate an incremental search. Control-G will abort an incremental search and restore the original line. When the search is terminated, the history entry containing the search string becomes the current line. To find other matching entries in the history list, type Control-S or Control-R as appropriate. This will search backward or forward in the history for the next entry matching the search string typed so far. Any other key sequence bound to a readline command will terminate the search and execute that command. For instance, a newline will termi- nate the search and accept the line, thereby executing the command from the history list. Readline remembers the last incremental search string. If two Control- Rs are typed without any intervening characters defining a new search string, any remembered search string is used. Non-incremental searches read the entire search string before starting to search for matching history lines. The search string may be typed by the user or be part of the contents of the current line. Readline Command Names The following is a list of the names of the commands and the default key sequences to which they are bound. Command names without an accom- panying key sequence are unbound by default. In the following descrip- tions, point refers to the current cursor position, and mark refers to a cursor position saved by the set-mark command. The text between the point and mark is referred to as the region. Commands for Moving beginning-of-line (C-a) Move to the start of the current line. end-of-line (C-e) Move to the end of the line. forward-char (C-f) Move forward a character. backward-char (C-b) Move back a character. forward-word (M-f) Move forward to the end of the next word. Words are composed of alphanumeric characters (letters and digits). backward-word (M-b) Move back to the start of the current or previous word. Words are composed of alphanumeric characters (letters and digits). shell-forward-word Move forward to the end of the next word. Words are delimited by non-quoted shell metacharacters. shell-backward-word Move back to the start of the current or previous word. Words are delimited by non-quoted shell metacharacters. previous-screen-line Attempt to move point to the same physical screen column on the previous physical screen line. This will not have the desired effect if the current Readline line does not take up more than one physical line or if point is not greater than the length of the prompt plus the screen width. next-screen-line Attempt to move point to the same physical screen column on the next physical screen line. This will not have the desired effect if the current Readline line does not take up more than one physical line or if the length of the current Readline line is not greater than the length of the prompt plus the screen width. clear-display (M-C-l) Clear the screen and, if possible, the terminal's scrollback buffer, then redraw the current line, leaving the current line at the top of the screen. clear-screen (C-l) Clear the screen, then redraw the current line, leaving the cur- rent line at the top of the screen. With an argument, refresh the current line without clearing the screen. redraw-current-line Refresh the current line. Commands for Manipulating the History accept-line (Newline, Return) Accept the line regardless of where the cursor is. If this line is non-empty, add it to the history list according to the state of the HISTCONTROL variable. If the line is a modified history line, then restore the history line to its original state. previous-history (C-p) Fetch the previous command from the history list, moving back in the list. next-history (C-n) Fetch the next command from the history list, moving forward in the list. beginning-of-history (M-<) Move to the first line in the history. end-of-history (M->) Move to the end of the input history, i.e., the line currently being entered. reverse-search-history (C-r) Search backward starting at the current line and moving `up' through the history as necessary. This is an incremental search. forward-search-history (C-s) Search forward starting at the current line and moving `down' through the history as necessary. This is an incremental search. non-incremental-reverse-search-history (M-p) Search backward through the history starting at the current line using a non-incremental search for a string supplied by the user. non-incremental-forward-search-history (M-n) Search forward through the history using a non-incremental search for a string supplied by the user. history-search-forward Search forward through the history for the string of characters between the start of the current line and the point. This is a non-incremental search. history-search-backward Search backward through the history for the string of characters between the start of the current line and the point. This is a non-incremental search. history-substring-search-backward Search backward through the history for the string of characters between the start of the current line and the current cursor po- sition (the point). The search string may match anywhere in a history line. This is a non-incremental search. history-substring-search-forward Search forward through the history for the string of characters between the start of the current line and the point. The search string may match anywhere in a history line. This is a non-in- cremental search. yank-nth-arg (M-C-y) Insert the first argument to the previous command (usually the second word on the previous line) at point. With an argument n, insert the nth word from the previous command (the words in the previous command begin with word 0). A negative argument in- serts the nth word from the end of the previous command. Once the argument n is computed, the argument is extracted as if the "!n" history expansion had been specified. yank-last-arg (M-., M-_) Insert the last argument to the previous command (the last word of the previous history entry). With a numeric argument, behave exactly like yank-nth-arg. Successive calls to yank-last-arg move back through the history list, inserting the last word (or the word specified by the argument to the first call) of each line in turn. Any numeric argument supplied to these successive calls determines the direction to move through the history. A negative argument switches the direction through the history (back or forward). The history expansion facilities are used to extract the last word, as if the "!$" history expansion had been specified. shell-expand-line (M-C-e) Expand the line as the shell does. This performs alias and his- tory expansion as well as all of the shell word expansions. See HISTORY EXPANSION below for a description of history expansion. history-expand-line (M-^) Perform history expansion on the current line. See HISTORY EX- PANSION below for a description of history expansion. magic-space Perform history expansion on the current line and insert a space. See HISTORY EXPANSION below for a description of history expansion. alias-expand-line Perform alias expansion on the current line. See ALIASES above for a description of alias expansion. history-and-alias-expand-line Perform history and alias expansion on the current line. insert-last-argument (M-., M-_) A synonym for yank-last-arg. operate-and-get-next (C-o) Accept the current line for execution and fetch the next line relative to the current line from the history for editing. A numeric argument, if supplied, specifies the history entry to use instead of the current line. edit-and-execute-command (C-x C-e) Invoke an editor on the current command line, and execute the result as shell commands. Bash attempts to invoke $VISUAL, $ED- ITOR, and emacs as the editor, in that order. Commands for Changing Text end-of-file (usually C-d) The character indicating end-of-file as set, for example, by ``stty''. If this character is read when there are no charac- ters on the line, and point is at the beginning of the line, Readline interprets it as the end of input and returns EOF. delete-char (C-d) Delete the character at point. If this function is bound to the same character as the tty EOF character, as C-d commonly is, see above for the effects. backward-delete-char (Rubout) Delete the character behind the cursor. When given a numeric argument, save the deleted text on the kill ring. forward-backward-delete-char Delete the character under the cursor, unless the cursor is at the end of the line, in which case the character behind the cur- sor is deleted. quoted-insert (C-q, C-v) Add the next character typed to the line verbatim. This is how to insert characters like C-q, for example. tab-insert (C-v TAB) Insert a tab character. self-insert (a, b, A, 1, !, ...) Insert the character typed. transpose-chars (C-t) Drag the character before point forward over the character at point, moving point forward as well. If point is at the end of the line, then this transposes the two characters before point. Negative arguments have no effect. transpose-words (M-t) Drag the word before point past the word after point, moving point over that word as well. If point is at the end of the line, this transposes the last two words on the line. upcase-word (M-u) Uppercase the current (or following) word. With a negative ar- gument, uppercase the previous word, but do not move point. downcase-word (M-l) Lowercase the current (or following) word. With a negative ar- gument, lowercase the previous word, but do not move point. capitalize-word (M-c) Capitalize the current (or following) word. With a negative ar- gument, capitalize the previous word, but do not move point. overwrite-mode Toggle overwrite mode. With an explicit positive numeric argu- ment, switches to overwrite mode. With an explicit non-positive numeric argument, switches to insert mode. This command affects only emacs mode; vi mode does overwrite differently. Each call to readline() starts in insert mode. In overwrite mode, charac- ters bound to self-insert replace the text at point rather than pushing the text to the right. Characters bound to back- ward-delete-char replace the character before point with a space. By default, this command is unbound. Killing and Yanking kill-line (C-k) Kill the text from point to the end of the line. backward-kill-line (C-x Rubout) Kill backward to the beginning of the line. unix-line-discard (C-u) Kill backward from point to the beginning of the line. The killed text is saved on the kill-ring. kill-whole-line Kill all characters on the current line, no matter where point is. kill-word (M-d) Kill from point to the end of the current word, or if between words, to the end of the next word. Word boundaries are the same as those used by forward-word. backward-kill-word (M-Rubout) Kill the word behind point. Word boundaries are the same as those used by backward-word. shell-kill-word Kill from point to the end of the current word, or if between words, to the end of the next word. Word boundaries are the same as those used by shell-forward-word. shell-backward-kill-word Kill the word behind point. Word boundaries are the same as those used by shell-backward-word. unix-word-rubout (C-w) Kill the word behind point, using white space as a word bound- ary. The killed text is saved on the kill-ring. unix-filename-rubout Kill the word behind point, using white space and the slash character as the word boundaries. The killed text is saved on the kill-ring. delete-horizontal-space (M-\) Delete all spaces and tabs around point. kill-region Kill the text in the current region. copy-region-as-kill Copy the text in the region to the kill buffer. copy-backward-word Copy the word before point to the kill buffer. The word bound- aries are the same as backward-word. copy-forward-word Copy the word following point to the kill buffer. The word boundaries are the same as forward-word. yank (C-y) Yank the top of the kill ring into the buffer at point. yank-pop (M-y) Rotate the kill ring, and yank the new top. Only works follow- ing yank or yank-pop. Numeric Arguments digit-argument (M-0, M-1, ..., M--) Add this digit to the argument already accumulating, or start a new argument. M-- starts a negative argument. universal-argument This is another way to specify an argument. If this command is followed by one or more digits, optionally with a leading minus sign, those digits define the argument. If the command is fol- lowed by digits, executing universal-argument again ends the nu- meric argument, but is otherwise ignored. As a special case, if this command is immediately followed by a character that is nei- ther a digit nor minus sign, the argument count for the next command is multiplied by four. The argument count is initially one, so executing this function the first time makes the argu- ment count four, a second time makes the argument count sixteen, and so on. Completing complete (TAB) Attempt to perform completion on the text before point. Bash attempts completion treating the text as a variable (if the text begins with $), username (if the text begins with ~), hostname (if the text begins with @), or command (including aliases and functions) in turn. If none of these produces a match, filename completion is attempted. possible-completions (M-?) List the possible completions of the text before point. insert-completions (M-*) Insert all completions of the text before point that would have been generated by possible-completions. menu-complete Similar to complete, but replaces the word to be completed with a single match from the list of possible completions. Repeated execution of menu-complete steps through the list of possible completions, inserting each match in turn. At the end of the list of completions, the bell is rung (subject to the setting of bell-style) and the original text is restored. An argument of n moves n positions forward in the list of matches; a negative ar- gument may be used to move backward through the list. This com- mand is intended to be bound to TAB, but is unbound by default. menu-complete-backward Identical to menu-complete, but moves backward through the list of possible completions, as if menu-complete had been given a negative argument. This command is unbound by default. delete-char-or-list Deletes the character under the cursor if not at the beginning or end of the line (like delete-char). If at the end of the line, behaves identically to possible-completions. This command is unbound by default. complete-filename (M-/) Attempt filename completion on the text before point. possible-filename-completions (C-x /) List the possible completions of the text before point, treating it as a filename. complete-username (M-~) Attempt completion on the text before point, treating it as a username. possible-username-completions (C-x ~) List the possible completions of the text before point, treating it as a username. complete-variable (M-$) Attempt completion on the text before point, treating it as a shell variable. possible-variable-completions (C-x $) List the possible completions of the text before point, treating it as a shell variable. complete-hostname (M-@) Attempt completion on the text before point, treating it as a hostname. possible-hostname-completions (C-x @) List the possible completions of the text before point, treating it as a hostname. complete-command (M-!) Attempt completion on the text before point, treating it as a command name. Command completion attempts to match the text against aliases, reserved words, shell functions, shell builtins, and finally executable filenames, in that order. possible-command-completions (C-x !) List the possible completions of the text before point, treating it as a command name. dynamic-complete-history (M-TAB) Attempt completion on the text before point, comparing the text against lines from the history list for possible completion matches. dabbrev-expand Attempt menu completion on the text before point, comparing the text against lines from the history list for possible completion matches. complete-into-braces (M-{) Perform filename completion and insert the list of possible com- pletions enclosed within braces so the list is available to the shell (see Brace Expansion above). Keyboard Macros start-kbd-macro (C-x () Begin saving the characters typed into the current keyboard macro. end-kbd-macro (C-x )) Stop saving the characters typed into the current keyboard macro and store the definition. call-last-kbd-macro (C-x e) Re-execute the last keyboard macro defined, by making the char- acters in the macro appear as if typed at the keyboard. print-last-kbd-macro () Print the last keyboard macro defined in a format suitable for the inputrc file. Miscellaneous re-read-init-file (C-x C-r) Read in the contents of the inputrc file, and incorporate any bindings or variable assignments found there. abort (C-g) Abort the current editing command and ring the terminal's bell (subject to the setting of bell-style). do-lowercase-version (M-A, M-B, M-x, ...) If the metafied character x is uppercase, run the command that is bound to the corresponding metafied lowercase character. The behavior is undefined if x is already lowercase. prefix-meta (ESC) Metafy the next character typed. ESC f is equivalent to Meta-f. undo (C-_, C-x C-u) Incremental undo, separately remembered for each line. revert-line (M-r) Undo all changes made to this line. This is like executing the undo command enough times to return the line to its initial state. tilde-expand (M-&) Perform tilde expansion on the current word. set-mark (C-@, M-<space>) Set the mark to the point. If a numeric argument is supplied, the mark is set to that position. exchange-point-and-mark (C-x C-x) Swap the point with the mark. The current cursor position is set to the saved position, and the old cursor position is saved as the mark. character-search (C-]) A character is read and point is moved to the next occurrence of that character. A negative count searches for previous occur- rences. character-search-backward (M-C-]) A character is read and point is moved to the previous occur- rence of that character. A negative count searches for subse- quent occurrences. skip-csi-sequence Read enough characters to consume a multi-key sequence such as those defined for keys like Home and End. Such sequences begin with a Control Sequence Indicator (CSI), usually ESC-[. If this sequence is bound to "\[", keys producing such sequences will have no effect unless explicitly bound to a readline command, instead of inserting stray characters into the editing buffer. This is unbound by default, but usually bound to ESC-[. insert-comment (M-#) Without a numeric argument, the value of the readline com- ment-begin variable is inserted at the beginning of the current line. If a numeric argument is supplied, this command acts as a toggle: if the characters at the beginning of the line do not match the value of comment-begin, the value is inserted, other- wise the characters in comment-begin are deleted from the begin- ning of the line. In either case, the line is accepted as if a newline had been typed. The default value of comment-begin causes this command to make the current line a shell comment. If a numeric argument causes the comment character to be re- moved, the line will be executed by the shell. glob-complete-word (M-g) The word before point is treated as a pattern for pathname ex- pansion, with an asterisk implicitly appended. This pattern is used to generate a list of matching filenames for possible com- pletions. glob-expand-word (C-x *) The word before point is treated as a pattern for pathname ex- pansion, and the list of matching filenames is inserted, replac- ing the word. If a numeric argument is supplied, an asterisk is appended before pathname expansion. glob-list-expansions (C-x g) The list of expansions that would have been generated by glob-expand-word is displayed, and the line is redrawn. If a numeric argument is supplied, an asterisk is appended before pathname expansion. dump-functions Print all of the functions and their key bindings to the read- line output stream. If a numeric argument is supplied, the out- put is formatted in such a way that it can be made part of an inputrc file. dump-variables Print all of the settable readline variables and their values to the readline output stream. If a numeric argument is supplied, the output is formatted in such a way that it can be made part of an inputrc file. dump-macros Print all of the readline key sequences bound to macros and the strings they output. If a numeric argument is supplied, the output is formatted in such a way that it can be made part of an inputrc file. display-shell-version (C-x C-v) Display version information about the current instance of bash. Programmable Completion When word completion is attempted for an argument to a command for which a completion specification (a compspec) has been defined using the complete builtin (see SHELL BUILTIN COMMANDS below), the program- mable completion facilities are invoked. First, the command name is identified. If the command word is the empty string (completion attempted at the beginning of an empty line), any compspec defined with the -E option to complete is used. If a compspec has been defined for that command, the compspec is used to generate the list of possible completions for the word. If the command word is a full pathname, a compspec for the full pathname is searched for first. If no compspec is found for the full pathname, an attempt is made to find a compspec for the portion following the final slash. If those searches do not result in a compspec, any compspec defined with the -D option to complete is used as the default. If there is no default compspec, bash attempts alias expansion on the command word as a final resort, and attempts to find a compspec for the command word from any successful expansion. Once a compspec has been found, it is used to generate the list of matching words. If a compspec is not found, the default bash comple- tion as described above under Completing is performed. First, the actions specified by the compspec are used. Only matches which are prefixed by the word being completed are returned. When the -f or -d option is used for filename or directory name completion, the shell variable FIGNORE is used to filter the matches. Any completions specified by a pathname expansion pattern to the -G op- tion are generated next. The words generated by the pattern need not match the word being completed. The GLOBIGNORE shell variable is not used to filter the matches, but the FIGNORE variable is used. Next, the string specified as the argument to the -W option is consid- ered. The string is first split using the characters in the IFS spe- cial variable as delimiters. Shell quoting is honored. Each word is then expanded using brace expansion, tilde expansion, parameter and variable expansion, command substitution, and arithmetic expansion, as described above under EXPANSION. The results are split using the rules described above under Word Splitting. The results of the expansion are prefix-matched against the word being completed, and the matching words become the possible completions. After these matches have been generated, any shell function or command specified with the -F and -C options is invoked. When the command or function is invoked, the COMP_LINE, COMP_POINT, COMP_KEY, and COMP_TYPE variables are assigned values as described above under Shell Variables. If a shell function is being invoked, the COMP_WORDS and COMP_CWORD variables are also set. When the function or command is invoked, the first argument ($1) is the name of the command whose arguments are be- ing completed, the second argument ($2) is the word being completed, and the third argument ($3) is the word preceding the word being com- pleted on the current command line. No filtering of the generated com- pletions against the word being completed is performed; the function or command has complete freedom in generating the matches. Any function specified with -F is invoked first. The function may use any of the shell facilities, including the compgen builtin described below, to generate the matches. It must put the possible completions in the COMPREPLY array variable, one per array element. Next, any command specified with the -C option is invoked in an envi- ronment equivalent to command substitution. It should print a list of completions, one per line, to the standard output. Backslash may be used to escape a newline, if necessary. After all of the possible completions are generated, any filter speci- fied with the -X option is applied to the list. The filter is a pat- tern as used for pathname expansion; a & in the pattern is replaced with the text of the word being completed. A literal & may be escaped with a backslash; the backslash is removed before attempting a match. Any completion that matches the pattern will be removed from the list. A leading ! negates the pattern; in this case any completion not match- ing the pattern will be removed. If the nocasematch shell option is enabled, the match is performed without regard to the case of alpha- betic characters. Finally, any prefix and suffix specified with the -P and -S options are added to each member of the completion list, and the result is returned to the readline completion code as the list of possible completions. If the previously-applied actions do not generate any matches, and the -o dirnames option was supplied to complete when the compspec was de- fined, directory name completion is attempted. If the -o plusdirs option was supplied to complete when the compspec was defined, directory name completion is attempted and any matches are added to the results of the other actions. By default, if a compspec is found, whatever it generates is returned to the completion code as the full set of possible completions. The default bash completions are not attempted, and the readline default of filename completion is disabled. If the -o bashdefault option was sup- plied to complete when the compspec was defined, the bash default com- pletions are attempted if the compspec generates no matches. If the -o default option was supplied to complete when the compspec was defined, readline's default completion will be performed if the compspec (and, if attempted, the default bash completions) generate no matches. When a compspec indicates that directory name completion is desired, the programmable completion functions force readline to append a slash to completed names which are symbolic links to directories, subject to the value of the mark-directories readline variable, regardless of the setting of the mark-symlinked-directories readline variable. There is some support for dynamically modifying completions. This is most useful when used in combination with a default completion speci- fied with complete -D. It's possible for shell functions executed as completion handlers to indicate that completion should be retried by returning an exit status of 124. If a shell function returns 124, and changes the compspec associated with the command on which completion is being attempted (supplied as the first argument when the function is executed), programmable completion restarts from the beginning, with an attempt to find a new compspec for that command. This allows a set of completions to be built dynamically as completion is attempted, rather than being loaded all at once. For instance, assuming that there is a library of compspecs, each kept in a file corresponding to the name of the command, the following de- fault completion function would load completions dynamically: _completion_loader() { . "/etc/bash_completion.d/$1.sh" >/dev/null 2>&1 && return 124 } complete -D -F _completion_loader -o bashdefault -o default

📜 HISTORY

When the -o history option to the set builtin is enabled, the shell provides access to the command history 📋, the list of commands previously typed. The value of the HISTSIZE variable is used as the number of commands to save in a history list. The text of the last HISTSIZE commands (default 500) is saved. The shell stores each command in the history list prior to parameter and variable expansion (see EXPANSION above) but after history expansion is performed, subject to the values of the shell variables HISTIGNORE and HISTCONTROL.

On startup 🚀, the history is initialized from the file named by the variable HISTFILE (default ~/.bash_history). The file named by the value of HISTFILE is truncated, if necessary, to contain no more than the number of lines specified by the value of HISTFILESIZE. If HISTFILESIZE is unset, or set to null, a non-numeric value, or a numeric value less than zero, the history file is not truncated. When the history file is read, lines beginning with the history comment character followed immediately by a digit are interpreted as timestamps ⏱️ for the following history line. These timestamps are optionally displayed depending on the value of the HISTTIMEFORMAT variable. When a shell with history enabled exits, the last $HISTSIZE lines are copied from the history list to $HISTFILE. If the histappend shell option is enabled (see the description of shopt under SHELL BUILTIN COMMANDS below), the lines are appended to the history file ➕, otherwise the history file is overwritten. If HISTFILE is unset, or if the history file is unwritable, the history is not saved. If the HISTTIMEFORMAT variable is set, time stamps are written to the history file, marked with the history comment character, so they may be preserved across shell sessions 🔒. This uses the history comment character to distinguish timestamps from other history lines. After saving the history, the history file is truncated to contain no more than HISTFILESIZE lines. If HISTFILESIZE is unset, or set to null, a non-numeric value, or a numeric value less than zero, the history file is not truncated.

The builtin command fc (see SHELL BUILTIN COMMANDS below) may be used to list or edit and re-execute a portion of the history list 🔄. The history builtin may be used to display or modify the history list and manipulate the history file. When using command-line editing, search commands are available in each editing mode that provide access to the history list 🔍.

The shell allows control over which commands are saved on the history list. The HISTCONTROL and HISTIGNORE variables may be set to cause the shell to save only a subset of the commands entered. The cmdhist shell option, if enabled, causes the shell to attempt to save each line of a multi-line command in the same history entry, adding semicolons where necessary to preserve syntactic correctness. The lithist shell option causes the shell to save the command with embedded newlines instead of semicolons. See the description of the shopt builtin below under SHELL BUILTIN COMMANDS for information on setting and unsetting shell options.

📜 HISTORY EXPANSION

🖥️ The shell supports a history expansion feature that is similar to the history expansion in csh. This section describes what syntax features are available. This feature is enabled by default for interactive shells, and can be disabled using the +H option to the set builtin command (see 📖 SHELL BUILTIN COMMANDS below). Non-interactive shells do not perform history expansion by default.

🔄 History expansions introduce words from the history list into the input stream, making it easy to repeat commands, insert the arguments to a previous command into the current input line, or fix errors in previous commands quickly.

⏱️ History expansion is performed immediately after a complete line is read, before the shell breaks it into words, and is performed on each line individually without taking quoting on previous lines into account. It takes place in two parts. The first is to determine which line from the history list to use during substitution. The second is to select portions of that line for inclusion into the current one. The line selected from the history is the event, and the portions of that line that are acted upon are words. Various modifiers are available to manipulate the selected words. The line is broken into words in the same fashion as when reading input, so that several metacharacter-separated words surrounded by quotes are considered one word. History expansions are introduced by the appearance of the history expansion character, which is ! by default. Only backslash (\) and single quotes can quote the history expansion character, but the history expansion character is also treated as quoted if it immediately precedes the closing double quote in a double-quoted string.

🚫 Several characters inhibit history expansion if found immediately following the history expansion character, even if it is unquoted: space, tab, newline, carriage return, and =. If the extglob shell option is enabled, ( will also inhibit expansion.

⚙️ Several shell options settable with the shopt builtin may be used to tailor the behavior of history expansion. If the histverify shell option is enabled (see the description of the shopt builtin below), and readline is being used, history substitutions are not immediately passed to the shell parser. Instead, the expanded line is reloaded into the readline editing buffer for further modification. If readline is being used, and the histreedit shell option is enabled, a failed history substitution will be reloaded into the readline editing buffer for correction. The -p option to the history builtin command may be used to see what a history expansion will do before using it. The -s option to the history builtin may be used to add commands to the end of the history list without actually executing them, so that they are available for subsequent recall.

🔧 The shell allows control of the various characters used by the history expansion mechanism (see the description of histchars above under Shell Variables). The shell uses the history comment character to mark history timestamps when writing the history file.

📌 Event Designators

An event designator is a reference to a command line entry in the history list. Unless the reference is absolute, events are relative to the current position in the history list.

• ! — Start a history substitution, except when followed by a blank, newline, carriage return, = or ( (when the extglob shell option is enabled using the shopt builtin).
• !n — Refer to command line n.
• !-n — Refer to the current command minus n.
• !! — Refer to the previous command. This is a synonym for !-1.
• !string — Refer to the most recent command preceding the current position in the history list starting with string.
• !?string[?] — Refer to the most recent command preceding the current position in the history list containing string. The trailing ? may be omitted if string is followed immediately by a newline. If string is missing, the string from the most recent search is used; it is an error if there is no previous search string.
• ^string1^string2^ — Quick substitution. Repeat the previous command, replacing string1 with string2. Equivalent to !!:s^string1^string2^ (see Modifiers below).
• !# — The entire command line typed so far.

📝 Word Designators

Word designators are used to select desired words from the event. A : separates the event specification from the word designator. It may be omitted if the word designator begins with a ^, $, *, -, or %. Words are numbered from the beginning of the line, with the first word being denoted by 0 (zero). Words are inserted into the current line separated by single spaces.

• 0 (zero) — The zeroth word. For the shell, this is the command word.
• n — The nth word.
• ^ — The first argument. That is, word 1.
• $ — The last word. This is usually the last argument, but will expand to the zeroth word if there is only one word in the line.
• % — The first word matched by the most recent ?string? search, if the search string begins with a character that is part of a word.
• x-y — A range of words; -y abbreviates 0-y.
• * — All of the words but the zeroth. This is a synonym for 1-$. It is not an error to use * if there is just one word in the event; the empty string is returned in that case.
• x* — Abbreviates x-$.
• x- — Abbreviates x-$ like x*, but omits the last word. If x is missing, it defaults to 0.

If a word designator is supplied without an event specification, the previous command is used as the event.

✂️ Modifiers

After the optional word designator, there may appear a sequence of one or more of the following modifiers, each preceded by a :. These modify, or edit, the word or words selected from the history event.

• h — Remove a trailing filename component, leaving only the head.
• t — Remove all leading filename components, leaving the tail.
• r — Remove a trailing suffix of the form .xxx, leaving the basename.
• e — Remove all but the trailing suffix.
• p — Print the new command but do not execute it.
• q — Quote the substituted words, escaping further substitutions.
• x — Quote the substituted words as with q, but break into words at blanks and newlines. The q and x modifiers are mutually exclusive; the last one supplied is used.
• s/old/new/ — Substitute new for the first occurrence of old in the event line. Any character may be used as the delimiter in place of /. The final delimiter is optional if it is the last character of the event line. The delimiter may be quoted in old and new with a single backslash. If & appears in new, it is replaced by old. A single backslash will quote the &. If old is null, it is set to the last old substituted, or, if no previous history substitutions took place, the last string in a !?string[?] search. If new is null, each matching old is deleted.
• & — Repeat the previous substitution.
• g — Cause changes to be applied over the entire event line. This is used in conjunction with :s (e.g., :gs/old/new/) or :&. If used with :s, any delimiter can be used in place of /, and the final delimiter is optional if it is the last character of the event line. An a may be used as a synonym for g.
• G — Apply the following s or & modifier once to each word in the event line.

🔧 SHELL BUILTIN COMMANDS

Unless otherwise noted, each builtin command documented in this section as accepting options preceded by - accepts -- to signify the end of the options. The :, true, false, and test/[ builtins do not accept options and do not treat -- specially. The exit, logout, return, break, continue, let, and shift builtins accept and process arguments beginning with - without requiring --. Other builtins that accept arguments but are not specified as accepting options interpret arguments beginning with - as invalid options and require -- to prevent this interpretation.

: 🛑 No effect

: [arguments] — No effect; the command does nothing beyond expanding arguments and performing any specified redirections. The return status is zero.

. / source 📂 Read and execute file

. filename [arguments]
source filename [arguments]

Read and execute commands from filename in the current shell environment and return the exit status of the last command executed from filename. If filename does not contain a slash, filenames in PATH are used to find the directory containing filename. The file searched for in PATH need not be executable. When bash is not in posix mode, the current directory is searched if no file is found in PATH. If the sourcepath option to the shopt builtin command is turned off, the PATH is not searched. If any arguments are supplied, they become the positional parameters when filename is executed. Otherwise the positional parameters are unchanged. If the -T option is enabled, source inherits any trap on DEBUG; if it is not, any DEBUG trap string is saved and restored around the call to source, and source unsets the DEBUG trap while it executes. If -T is not set, and the sourced file changes the DEBUG trap, the new value is retained when source completes. The return status is the status of the last command exited within the script (0 if no commands are executed), and false if filename is not found or cannot be read.

alias 🔗 Define or display aliases

alias [-p] [name[=value] ...]

Alias with no arguments or with the -p option prints the list of aliases in the form alias name=value on standard output. When arguments are supplied, an alias is defined for each name whose value is given. A trailing space in value causes the next word to be checked for alias substitution when the alias is expanded. For each name in the argument list for which no value is supplied, the name and value of the alias is printed. Alias returns true unless a name is given for which no alias has been defined.

bg ⏯️ Resume job in background

bg [jobspec ...]

Resume each suspended job jobspec in the background, as if it had been started with &. If jobspec is not present, the shell's notion of the current job is used. bg jobspec returns 0 unless run when job control is disabled or, when run with job control enabled, any specified jobspec was not found or was started without job control.

bind ⌨️ Display/set readline key bindings

bind [-m keymap] [-lpsvPSVX]
bind [-m keymap] [-q function] [-u function] [-r keyseq]
bind [-m keymap] -f filename
bind [-m keymap] -x keyseq:shell-command
bind [-m keymap] keyseq:function-name
bind [-m keymap] keyseq:readline-command

Display current readline key and function bindings, bind a key sequence to a readline function or macro, or set a readline variable. Each non-option argument is a command as it would appear in .inputrc, but each binding or command must be passed as a separate argument; e.g., '\C-x\C-r': re-read-init-file. Options, if supplied, have the following meanings:

• -m keymap 🎯 Use keymap as the keymap to be affected by the subsequent bindings. Acceptable keymap names are emacs, emacs-standard, emacs-meta, emacs-ctlx, vi, vi-move, vi-command, and vi-insert. vi is equivalent to vi-command (vi-move is also a synonym); emacs is equivalent to emacs-standard.
• -l 📋 List the names of all readline functions.
• -p 🖨️ Display readline function names and bindings in such a way that they can be re-read.
• -P 📋 List current readline function names and bindings.
• -s 📋 Display readline key sequences bound to macros and the strings they output in such a way that they can be re-read.
• -S 📋 Display readline key sequences bound to macros and the strings they output.
• -v 📋 Display readline variable names and values in such a way that they can be re-read.
• -V 📋 List current readline variable names and values.
• -f filename 📂 Read key bindings from filename.
• -q function ❓ Query about which keys invoke the named function.
• -u function ❌ Unbind all keys bound to the named function.
• -r keyseq ❌ Remove any current binding for keyseq.
• -x keyseq:shell-command ⚡ Cause shell-command to be executed whenever keyseq is entered. When shell-command is executed, the shell sets the READLINE_LINE variable to the contents of the readline line buffer and the READLINE_POINT and READLINE_MARK variables to the current location of the insertion point and the saved insertion point (the mark), respectively. If the executed command changes the value of any of READLINE_LINE, READLINE_POINT, or READLINE_MARK, those new values will be reflected in the editing state.
• -X 📋 List all key sequences bound to shell commands and the associated commands in a format that can be reused as input.

The return value is 0 unless an unrecognized option is given or an error occurred.

break 🚫 Exit from loop

break [n]

Exit from within a for, while, until, or select loop. If n is specified, break n levels. n must be >= 1. If n is greater than the number of enclosing loops, all enclosing loops are exited. The return value is 0 unless n is not greater than or equal to 1.

builtin 🏗️ Execute builtin command

builtin shell-builtin [arguments]

Execute the specified shell builtin, passing it arguments, and return its exit status. This is useful when defining a function whose name is the same as a shell builtin, retaining the functionality of the builtin within the function. The cd builtin is commonly redefined this way. The return status is false if shell-builtin is not a shell builtin command.

caller 📞 Show call stack context

caller [expr]

Returns the context of any active subroutine call (a shell function or a script executed with the . or source builtins). Without expr, caller displays the line number and source filename of the current subroutine call. If a non-negative integer is supplied as expr, caller displays the line number, subroutine name, and source file corresponding to that position in the current execution call stack. This extra information may be used, for example, to print a stack trace. The current frame is frame 0. The return value is 0 unless the shell is not executing a subroutine call or expr does not correspond to a valid position in the call stack.

cd 📁 Change directory

cd [-L|[-P [-e]] [-@]] [dir]

Change the current directory to dir. If dir is not supplied, the value of the HOME shell variable is the default. Any additional arguments following dir are ignored. The variable CDPATH defines the search path for the directory containing dir: each directory name in CDPATH is searched for dir. Alternative directory names in CDPATH are separated by a colon (:). A null directory name in CDPATH is the same as the current directory, i.e., .. If dir begins with a slash (/), then CDPATH is not used. The -P option causes cd to use the physical directory structure by resolving symbolic links while traversing dir and before processing instances of .. in dir (see also the -P option to the set builtin command); the -L option forces symbolic links to be followed by resolving the link after processing instances of .. in dir. If .. appears in dir, it is processed by removing the immediately previous pathname component from dir, back to a slash or the beginning of dir. If the -e option is supplied with -P, and the current working directory cannot be successfully determined after a successful directory change, cd will return an unsuccessful status. On systems that support it, the -@ option presents the extended attributes associated with a file as a directory. An argument of - is converted to $OLDPWD before the directory change is attempted. If a non-empty directory name from CDPATH is used, or if - is the first argument, and the directory change is successful, the absolute pathname of the new working directory is written to the standard output. The return value is true if the directory was successfully changed; false otherwise.

command ⚙️ Run command without shell function lookup

command [-pVv] command [arg ...]

Run command with args suppressing the normal shell function lookup. Only builtin commands or commands found in the PATH are executed. If the -p option is given, the search for command is performed using a default value for PATH that is guaranteed to find all of the standard utilities. If either the -V or -v option is supplied, a description of command is printed. The -v option causes a single word indicating the command or filename used to invoke command to be displayed; the -V option produces a more verbose description. If the -V or -v option is supplied, the exit status is 0 if command was found, and 1 if not. If neither option is supplied and an error occurred or command cannot be found, the exit status is 127. Otherwise, the exit status of the command builtin is the exit status of command.

compgen 🎯 Generate completion matches

compgen [option] [word]

Generate possible completion matches for word according to the options, which may be any option accepted by the complete builtin with the exception of -p and -r, and write the matches to the standard output. When using the -F or -C options, the various shell variables set by the programmable completion facilities, while available, will not have useful values.

The matches will be generated in the same way as if the programmable completion code had generated them directly from a completion specification with the same flags. If word is specified, only those completions matching word will be displayed.

The return value is true unless an invalid option is supplied, or no matches were generated.

complete ✅ Specify how to complete arguments

complete [-abcdefgjksuv] [-o comp-option] [-DEI] [-A action] [-G globpat] [-W wordlist] [-F function] [-C command] [-X filterpat] [-P prefix] [-S suffix] name [name ...]
complete -pr [-DEI] [name ...]

Specify how arguments to each name should be completed. If the -p option is supplied, or if no options are supplied, existing completion specifications are printed in a way that allows them to be reused as input. The -r option removes a completion specification for each name, or, if no names are supplied, all completion specifications. The -D option indicates that other supplied options and actions should apply to the "default" command completion; that is, completion attempted on a command for which no completion has previously been defined. The -E option indicates that other supplied options and actions should apply to "empty" command completion; that is, completion attempted on a blank line. The -I option indicates that other supplied options and actions should apply to completion on the initial non-assignment word on the line, or after a command delimiter such as ; or |, which is usually command name completion. If multiple options are supplied, the -D option takes precedence over -E, and both take precedence over -I. If any of -D, -E, or -I are supplied, any other name arguments are ignored; these completions only apply to the case specified by the option.

The process of applying these completion specifications when word completion is attempted is described above under Programmable Completion.

Other options, if specified, have the following meanings. The arguments to the -G, -W, and -X options (and, if necessary, the -P and -S options) should be quoted to protect them from expansion before the complete builtin is invoked.

• -o comp-option 🎯 The comp-option controls several aspects of the comp-spec's behavior beyond the simple generation of completions. comp-option may be one of:
  • bashdefault — Perform the rest of the default bash completions if the compspec generates no matches.
  • default — Use readline's default filename completion if the compspec generates no matches.
  • dirnames — Perform directory name completion if the compspec generates no matches.
  • filenames — Tell readline that the compspec generates filenames, so it can perform any filename-specific processing (like adding a slash to directory names, quoting special characters, or suppressing trailing spaces). Intended to be used with shell functions.
  • noquote — Tell readline not to quote the completed words if they are filenames (quoting filenames is the default).
  • nosort — Tell readline not to sort the list of possible completions alphabetically.
  • nospace — Tell readline not to append a space (the default) to words completed at the end of the line.
  • plusdirs — After any matches defined by the compspec are generated, directory name completion is attempted and any matches are added to the results of the other actions.
• -A action 🎯 The action may be one of the following to generate a list of possible completions:
  • alias — Alias names. May also be specified as -a.
  • arrayvar — Array variable names.
  • binding — Readline key binding names.
  • builtin — Names of shell builtin commands. May also be specified as -b.
  • command — Command names. May also be specified as -c.
  • directory — Directory names. May also be specified as -d.
  • disabled — Names of disabled shell builtins.
  • enabled — Names of enabled shell builtins.
  • export — Names of exported shell variables. May also be specified as -e.
  • file — File names. May also be specified as -f.
  • function — Names of shell functions.
  • group — Group names. May also be specified as -g.
  • helptopic — Help topics as accepted by the help builtin.
  • hostname — Hostnames, as taken from the file specified by the HOSTFILE shell variable.
  • job — Job names, if job control is active. May also be specified as -j.
  • keyword — Shell reserved words. May also be specified as -k.
  • running — Names of running jobs, if job control is active.
  • service — Service names. May also be specified as -s.
  • setopt — Valid arguments for the -o option to the set builtin.
  • shopt — Shell option names as accepted by the shopt builtin.
  • signal — Signal names.
  • stopped — Names of stopped jobs, if job control is active.
  • user — User names. May also be specified as -u.
  • variable — Names of all shell variables. May also be specified as -v.
• -C command ⚡ command is executed in a subshell environment, and its output is used as the possible completions.
• -F function 🔧 The shell function function is executed in the current shell environment. When the function is executed, the first argument ($1) is the name of the command whose arguments are being completed, the second argument ($2) is the word being completed, and the third argument ($3) is the word preceding the word being completed on the current command line. When it finishes, the possible completions are retrieved from the value of the COMPREPLY array variable.
• -G globpat 🔍 The pathname expansion pattern globpat is expanded to generate the possible completions.
• -P prefix ➕ prefix is added at the beginning of each possible completion after all other options have been applied.
• -S suffix ➕ suffix is appended to each possible completion after all other options have been applied.
• -W wordlist 📋 The wordlist is split using the characters in the IFS special variable as delimiters, and each resultant word is expanded. Shell quoting is honored within wordlist, in order to provide a mechanism for the words to contain shell metacharacters or characters in the value of IFS. The possible completions are the members of the resultant list which match the word being completed.
• -X filterpat ❌ filterpat is a pattern as used for pathname expansion. It is applied to the list of possible completions generated by the preceding options and arguments, and each completion matching filterpat is removed from the list. A leading ! in filterpat negates the pattern; in this case, any completion not matching filterpat is removed.

The return value is true unless an invalid option is supplied, an option other than -p or -r is supplied without a name argument, an attempt is made to remove a completion specification for a name for which no specification exists, or an error occurs adding a completion specification.

compopt ⚙️ Modify completion options

compopt [-o option] [-DEI] [+o option] [name]

Modify completion options for each name according to the options, or for the currently-executing completion if no names are supplied. If no options are given, display the completion options for each name or the current completion. The possible values of option are those valid for the complete builtin described above. The -D option indicates that other supplied options should apply to the "default" command completion; that is, completion attempted on a command for which no completion has previously been defined. The -E option indicates that other supplied options should apply to "empty" command completion; that is, completion attempted on a blank line. The -I option indicates that other supplied options should apply to completion on the initial non-assignment word on the line, or after a command delimiter such as ; or |, which is usually command name completion.

The return value is true unless an invalid option is supplied, an attempt is made to modify the options for a name for which no completion specification exists, or an output error occurs.

continue 🔄 Resume next loop iteration

continue [n]

Resume the next iteration of the enclosing for, while, until, or select loop. If n is specified, resume at the nth enclosing loop. n must be >= 1. If n is greater than the number of enclosing loops, the last enclosing loop (the "top-level" loop) is resumed. The return value is 0 unless n is not greater than or equal to 1.

declare / typeset 📝 Declare variables and attributes

declare [-aAfFgiIlnrtux] [-p] [name[=value] ...]
typeset [-aAfFgiIlnrtux] [-p] [name[=value] ...]

Declare variables and/or give them attributes. If no names are given then display the values of variables. The -p option will display the attributes and values of each name. When -p is used with name arguments, additional options, other than -f and -F, are ignored. When -p is supplied without name arguments, it will display the attributes and values of all variables having the attributes specified by the additional options. If no other options are supplied with -p, declare will display the attributes and values of all shell variables. The -f option will restrict the display to shell functions. The -F option inhibits the display of function definitions; only the function name and attributes are printed. If the extdebug shell option is enabled using shopt, the source file name and line number where each name is defined are displayed as well. The -F option implies -f. The -g option forces variables to be created or modified at the global scope, even when declare is executed in a shell function. It is ignored in all other cases. The -I option causes local variables to inherit the attributes (except the nameref attribute) and value of any existing variable with the same name at a surrounding scope. If there is no existing variable, the local variable is initially unset. The following options can be used to restrict output to variables with the specified attribute or to give variables attributes:

• -a 📦 Each name is an indexed array variable (see Arrays above).
• -A 📦 Each name is an associative array variable (see Arrays above).
• -f 🔧 Use function names only.
• -i 🔢 The variable is treated as an integer; arithmetic evaluation (see ARITHMETIC EVALUATION above) is performed when the variable is assigned a value.
• -l 🔡 When the variable is assigned a value, all upper-case characters are converted to lower-case. The upper-case attribute is disabled.
• -n 🔗 Give each name the nameref attribute, making it a name reference to another variable. That other variable is defined by the value of name. All references, assignments, and attribute modifications to name, except those using or changing the -n attribute itself, are performed on the variable referenced by name's value. The nameref attribute cannot be applied to array variables.
• -r 🔒 Make names readonly. These names cannot then be assigned values by subsequent assignment statements or unset.
• -t 🏷️ Give each name the trace attribute. Traced functions inherit the DEBUG and RETURN traps from the calling shell. The trace attribute has no special meaning for variables.
• -u 🔠 When the variable is assigned a value, all lower-case characters are converted to upper-case. The lower-case attribute is disabled.
• -x 📤 Mark names for export to subsequent commands via the environment.

Using + instead of - turns off the attribute instead, with the exceptions that +a and +A may not be used to destroy array variables and +r will not remove the readonly attribute. When used in a function, declare and typeset make each name local, as with the local command, unless the -g option is supplied. If a variable name is followed by =value, the value of the variable is set to value. When using -a or -A and the compound assignment syntax to create array variables, additional attributes do not take effect until subsequent assignments. The return value is 0 unless an invalid option is encountered, an attempt is made to define a function using -f foo=bar, an attempt is made to assign a value to a readonly variable, an attempt is made to assign a value to an array variable without using the compound assignment syntax (see Arrays above), one of the names is not a valid shell variable name, an attempt is made to turn off readonly status for a readonly variable, an attempt is made to turn off array status for an array variable, or an attempt is made to display a non-existent function with -f.

dirs 📂 Display directory stack

dirs [-clpv] [+n] [-n]

Without options, displays the list of currently remembered directories. The default display is on a single line with directory names separated by spaces. Directories are added to the list with the pushd command; the popd command removes entries from the list. The current directory is always the first directory in the stack.

• -c 🗑️ Clears the directory stack by deleting all of the entries.
• -l 📋 Produces a listing using full pathnames; the default listing format uses a tilde to denote the home directory.
• -p 🖨️ Print the directory stack with one entry per line.
• -v 🖨️ Print the directory stack with one entry per line, prefixing each entry with its index in the stack.
• +n ➡️ Displays the nth entry counting from the left of the list shown by dirs when invoked without options, starting with zero.
• -n ⬅️ Displays the nth entry counting from the right of the list shown by dirs when invoked without options, starting with zero.

The return value is 0 unless an invalid option is supplied or n indexes beyond the end of the directory stack.

disown 🚫 Remove jobs from active table

disown [-ar] [-h] [jobspec ... | pid ... ]

Without options, remove each jobspec from the table of active jobs. If jobspec is not present, and neither the -a nor the -r option is supplied, the current job is used. If the -h option is given, each jobspec is not removed from the table, but is marked so that SIGHUP is not sent to the job if the shell receives a SIGHUP. If no jobspec is supplied, the -a option means to remove or mark all jobs; the -r option without a jobspec argument restricts operation to running jobs. The return value is 0 unless a jobspec does not specify a valid job.

echo 🔊 Output arguments

echo [-neE] [arg ...]

Output the args, separated by spaces, followed by a newline. The return status is 0 unless a write error occurs. If -n is specified, the trailing newline is suppressed. If the -e option is given, interpretation of the following backslash-escaped characters is enabled. The -E option disables the interpretation of these escape characters, even on systems where they are interpreted by default. The xpg_echo shell option may be used to dynamically determine whether or not echo expands these escape characters by default. echo does not interpret -- to mean the end of options. echo interprets the following escape sequences:

• \a 🔔 alert (bell)
• \b ⌫ backspace
• \c 🛑 suppress further output
• \e, \E escape character
• \f 📄 form feed
• \n ↩️ new line
• \r ⏎ carriage return
• \t ↹ horizontal tab
• \v ⬇️ vertical tab
• \\ backslash
• \0nnn the eight-bit character whose value is the octal value nnn (zero to three octal digits)
• \xHH the eight-bit character whose value is the hexadecimal value HH (one or two hex digits)
• \uHHHH the Unicode (ISO/IEC 10646) character whose value is the hexadecimal value HHHH (one to four hex digits)
• \UHHHHHHHH the Unicode (ISO/IEC 10646) character whose value is the hexadecimal value HHHHHHHH (one to eight hex digits)

enable 🔛 Enable/disable builtin commands

enable [-a] [-dnps] [-f filename] [name ...]

Enable and disable builtin shell commands. Disabling a builtin allows a disk command which has the same name as a shell builtin to be executed without specifying a full pathname, even though the shell normally searches for builtins before disk commands. If -n is used, each name is disabled; otherwise, names are enabled. For example, to use the test binary found via the PATH instead of the shell builtin version, run enable -n test. The -f option means to load the new builtin command name from shared object filename, on systems that support dynamic loading. The -d option will delete a builtin previously loaded with -f. If no name arguments are given, or if the -p option is supplied, a list of shell builtins is printed. With no other option arguments, the list consists of all enabled shell builtins. If -n is supplied, only disabled builtins are printed. If -a is supplied, the list printed includes all builtins, with an indication of whether or not each is enabled. If -s is supplied, the output is restricted to the POSIX special builtins. The return value is 0 unless a name is not a shell builtin or there is an error loading a new builtin from a shared object.

eval 🔄 Evaluate arguments as command

eval [arg ...]

The args are read and concatenated together into a single command. This command is then read and executed by the shell, and its exit status is returned as the value of eval. If there are no args, or only null arguments, eval returns 0.

exec 🚀 Execute command replacing shell

exec [-cl] [-a name] [command [arguments]]

If command is specified, it replaces the shell. No new process is created. The arguments become the arguments to command. If the -l option is supplied, the shell places a dash at the beginning of the zeroth argument passed to command. This is what gin(1) does. The -c option causes command to be executed with an empty environment. If -a is supplied, the shell passes name as the zeroth argument to the executed command. If command cannot be executed for some reason, a non-interactive shell exits, unless the execfail shell option is enabled. In that case, it returns failure. An interactive shell returns failure if the file cannot be executed. A subshell exits unconditionally if exec fails. If command is not specified, any redirections take effect in the current shell, and the return status is 0. If there is a redirection error, the return status is 1.

exit 🚪 Exit the shell

exit [n]

Cause the shell to exit with a status of n. If n is omitted, the exit status is that of the last command executed. A trap on EXIT is executed before the shell terminates.

export 📤 Export variables to environment

export [-fn] [name[=word]] ...
export -p

The supplied names are marked for automatic export to the environment of subsequently executed commands. If the -f option is given, the names refer to functions. If no names are given, or if the -p option is supplied, a list of names of all exported variables is printed. The -n option causes the export property to be removed from each name. If a variable name is followed by =word, the value of the variable is set to word. export returns an exit status of 0 unless an invalid option is encountered, one of the names is not a valid shell variable name, or -f is supplied with a name that is not a function.

fc 📜 Fix history command

fc [-e ename] [-lnr] [first] [last]
fc -s [pat=rep] [cmd]

The first form selects a range of commands from first to last from the history list and displays or edits and re-executes them. First and last may be specified as a string (to locate the last command beginning with that string) or as a number (an index into the history list, where a negative number is used as an offset from the current command number). When listing, a first or last of 0 is equivalent to -1 and -0 is equivalent to the current command (usually the fc command); otherwise 0 is equivalent to -1 and -0 is invalid. If last is not specified, it is set to the current command for listing (so that fc -l -10 prints the last 10 commands) and to first otherwise. If first is not specified, it is set to the previous command for editing and -16 for listing.

The -n option suppresses the command numbers when listing. The -r option reverses the order of the commands. If the -l option is given, the commands are listed on standard output. Otherwise, the editor given by ename is invoked on a file containing those commands. If ename is not given, the value of the FCEDIT variable is used, and the value of EDITOR if FCEDIT is not set. If neither variable is set, vi is used. When editing is complete, the edited commands are echoed and executed.

In the second form, command is re-executed after each instance of pat is replaced by rep. Command is interpreted the same as first above. A useful alias to use with this is r="fc -s", so that typing r cc runs the last command beginning with cc and typing r re-executes the last command.

If the first form is used, the return value is 0 unless an invalid option is encountered or first or last specify history lines out of range. If the -e option is supplied, the return value is the value of the last command executed or failure if an error occurs with the temporary file of commands. If the second form is used, the return status is that of the command re-executed, unless cmd does not specify a valid history line, in which case fc returns failure.

fg 🖥️ Bring job to foreground

fg [jobspec]

Resume jobspec in the foreground, and make it the current job. If jobspec is not present, the shell's notion of the current job is used. The return value is that of the command placed into the foreground, or failure if run when job control is disabled or, when run with job control enabled, if jobspec does not specify a valid job or jobspec specifies a job that was started without job control.

getopts ⚙️ Parse positional parameters

getopts optstring name [arg ...]

getopts is used by shell procedures to parse positional parameters. optstring contains the option characters to be recognized; if a character is followed by a colon, the option is expected to have an argument, which should be separated from it by white space. The colon and question mark characters may not be used as option characters. Each time it is invoked, getopts places the next option in the shell variable name, initializing name if it does not exist, and the index of the next argument to be processed into the variable OPTIND. OPTIND is initialized to 1 each time the shell or a shell script is invoked. When an option requires an argument, getopts places that argument into the variable OPTARG. The shell does not reset OPTIND automatically; it must be manually reset between multiple calls to getopts within the same shell invocation if a new set of parameters is to be used.

When the end of options is encountered, getopts exits with a return value greater than zero. OPTIND is set to the index of the first non-option argument, and name is set to ?.

getopts normally parses the positional parameters, but if more arguments are supplied as arg values, getopts parses those instead.

getopts can report errors in two ways. If the first character of optstring is a colon, silent error reporting is used. In normal operation, diagnostic messages are printed when invalid options or missing option arguments are encountered. If the variable OPTERR is set to 0, no error messages will be displayed, even if the first character of optstring is not a colon.

If an invalid option is seen, getopts places ? into name and, if not silent, prints an error message and unsets OPTARG. If getopts is silent, the option character found is placed in OPTARG and no diagnostic message is printed.

If a required argument is not found, and getopts is not silent, a question mark (?) is placed in name, OPTARG is unset, and a diagnostic message is printed. If getopts is silent, then a colon (:) is placed in name and OPTARG is set to the option character found.

getopts returns true if an option, specified or unspecified, is found. It returns false if the end of options is encountered or an error occurs.

hash 🔍 Hash commands for fast lookup

hash [-lr] [-p filename] [-dt] [name]

Each time hash is invoked, the full pathname of the command name is determined by searching the directories in $PATH and remembered. Any previously-remembered pathname is discarded. If the -p option is supplied, no path search is performed, and filename is used as the full filename of the command. The -r option causes the shell to forget all remembered locations. The -d option causes the shell to forget the remembered location of each name. If the -t option is supplied, the full pathname to which each name corresponds is printed. If multiple name arguments are supplied with -t, the name is printed before the hashed full pathname. The -l option causes output to be displayed in a format that may be reused as input. If no arguments are given, or if only -l is supplied, information about remembered commands is printed. The return status is true unless a name is not found or an invalid option is supplied.

help ❓ Display help for builtins

help [-dms] [pattern]

Display helpful information about builtin commands. If pattern is specified, help gives detailed help on all commands matching pattern; otherwise help for all the builtins and shell control structures is printed.

• -d 📝 Display a short description of each pattern
• -m 📄 Display the description of each pattern in a manpage-like format
• -s 📋 Display only a short usage synopsis for each pattern

The return status is 0 unless no command matches pattern.

history 📜 Manage command history

history [n]
history -c
history -d offset
history -d start-end
history -anrw [filename]
history -p arg [arg ...]
history -s arg [arg ...]

With no options, display the command history list with line numbers. Lines listed with a * have been modified. An argument of n lists only the last n lines. If the shell variable HISTTIMEFORMAT is set and not null, it is used as a format string for strftime(3) to display the time stamp associated with each displayed history entry. No intervening blank is printed between the formatted time stamp and the history line. If filename is supplied, it is used as the name of the history file; if not, the value of HISTFILE is used. Options, if supplied, have the following meanings:

• -c 🗑️ Clear the history list by deleting all the entries.
• -d offset ❌ Delete the history entry at position offset. If offset is negative, it is interpreted as relative to one greater than the last history position, so negative indices count back from the end of the history, and an index of -1 refers to the current history -d command.
• -d start-end ❌ Delete the history entries between positions start and end, inclusive. Positive and negative values for start and end are interpreted as described above.
• -a ➕ Append the "new" history lines to the history file. These are history lines entered since the beginning of the current bash session, but not already appended to the history file.
• -n 📖 Read the history lines not already read from the history file into the current history list. These are lines appended to the history file since the beginning of the current bash session.
• -r 📖 Read the contents of the history file and append them to the current history list.
• -w 💾 Write the current history list to the history file, overwriting the history file's contents.
• -p 🔄 Perform history substitution on the following args and display the result on the standard output. Does not store the results in the history list. Each arg must be quoted to disable normal history expansion.
• -s 💾 Store the args in the history list as a single entry. The last command in the history list is removed before the args are added.

If the HISTTIMEFORMAT variable is set, the time stamp information associated with each history entry is written to the history file, marked with the history comment character. When the history file is read, lines beginning with the history comment character followed immediately by a digit are interpreted as timestamps for the following history entry. The return value is 0 unless an invalid option is encountered, an error occurs while reading or writing the history file, an invalid offset is supplied as an argument to -d, or the history expansion supplied as an argument to -p fails.

jobs 📋 List active jobs

jobs [-lnprs] [ jobspec ... ]
jobs -x command [ args ... ]

The first form lists the active jobs. The options have the following meanings:

• -l 📋 List process IDs in addition to the normal information.
• -n 🔔 Display information only about jobs that have changed status since the user was last notified of their status.
• -p 📋 List only the process ID of the job's process group leader.
• -r ▶️ Display only running jobs.
• -s ⏸️ Display only stopped jobs.

If jobspec is given, output is restricted to information about that job. The return status is 0 unless an invalid option is encountered or an invalid jobspec is supplied.

If the -x option is supplied, jobs replaces any jobspec found in command or args with the corresponding process group ID, and executes command passing it args, returning its exit status.

kill 💀 Send signal to processes

kill [-s sigspec | -n signum | -sigspec] [pid | jobspec] ...
kill -l|-L [sigspec | exit_status]

Send the signal named by sigspec or signum to the processes named by pid or jobspec. sigspec is either a case-insensitive signal name such as SIGKILL (with or without the SIG prefix) or a signal number; signum is a signal number. If sigspec is not present, then SIGTERM is assumed. An argument of -l lists the signal names. If any arguments are supplied when -l is given, the names of the signals corresponding to the arguments are listed, and the return status is 0. The exit_status argument to -l is a number specifying either a signal number or the exit status of a process terminated by a signal. The -L option is equivalent to -l. kill returns true if at least one signal was successfully sent, or false if an error occurs or an invalid option is encountered.

let 🔢 Evaluate arithmetic expressions

let arg [arg ...]

Each arg is an arithmetic expression to be evaluated (see ARITHMETIC EVALUATION above). If the last arg evaluates to 0, let returns 1; 0 is returned otherwise.

local 📍 Define local variables

local [option] [name[=value] ... | - ]

For each argument, a local variable named name is created, and assigned value. The option can be any of the options accepted by declare. When local is used within a function, it causes the variable name to have a visible scope restricted to that function and its children. If name is -, the set of shell options is made local to the function in which local is invoked: shell options changed using the set builtin inside the function are restored to their original values when the function returns. The restore is effected as if a series of set commands were executed to restore the values that were in place before the function. With no operands, local writes a list of local variables to the standard output. It is an error to use local when not within a function. The return status is 0 unless local is used outside a function, an invalid name is supplied, or name is a readonly variable.

logout 🚪 Exit a login shell

logout — Exit a login shell.

mapfile / readarray 📄 Read lines into array

mapfile [-d delim] [-n count] [-O origin] [-s count] [-t] [-u fd] [-C callback] [-c quantum] [array]
readarray [-d delim] [-n count] [-O origin] [-s count] [-t] [-u fd] [-C callback] [-c quantum] [array]

Read lines from the standard input into the indexed array variable array, or from file descriptor fd if the -u option is supplied. The variable MAPFILE is the default array. Options, if supplied, have the following meanings:

• -d 🔤 The first character of delim is used to terminate each input line, rather than newline. If delim is the empty string, mapfile will terminate a line when it reads a NUL character.
• -n 🔢 Copy at most count lines. If count is 0, all lines are copied.
• -O 🔢 Begin assigning to array at index origin. The default index is 0.
• -s ⏭️ Discard the first count lines read.
• -t ✂️ Remove a trailing delim (default newline) from each line read.
• -u 📂 Read lines from file descriptor fd instead of the standard input.
• -C 🔄 Evaluate callback each time quantum lines are read. The -c option specifies quantum.
• -c 🔢 Specify the number of lines read between each call to callback.

If -C is specified without -c, the default quantum is 5000. When callback is evaluated, it is supplied the index of the next array element to be assigned and the line to be assigned to that element as additional arguments. callback is evaluated after the line is read but before the array element is assigned.

If not supplied with an explicit origin, mapfile will clear array before assigning to it.

mapfile returns successfully unless an invalid option or option argument is supplied, array is invalid or unassignable, or if array is not an indexed array.

popd 📤 Remove directory from stack

popd [-n] [+n] [-n]

Removes entries from the directory stack. With no arguments, removes the top directory from the stack, and performs a cd to the new top directory. Arguments, if supplied, have the following meanings:

• -n 🚫 Suppresses the normal change of directory when removing directories from the stack, so that only the stack is manipulated.
• +n ➡️ Removes the nth entry counting from the left of the list shown by dirs, starting with zero. For example: popd +0 removes the first directory, popd +1 the second.
• -n ⬅️ Removes the nth entry counting from the right of the list shown by dirs, starting with zero. For example: popd -0 removes the last directory, popd -1 the next to last.

If the popd command is successful, a dirs is performed as well, and the return status is 0. popd returns false if an invalid option is encountered, the directory stack is empty, a non-existent directory stack entry is specified, or the directory change fails.

printf 🖨️ Format and print data

printf [-v var] format [arguments]

Write the formatted arguments to the standard output under the control of the format. The -v option causes the output to be assigned to the variable var rather than being printed to the standard output.

The format is a character string which contains three types of objects: plain characters, which are simply copied to standard output, character escape sequences, which are converted and copied to the standard output, and format specifications, each of which causes printing of the next successive argument. In addition to the standard printf(1) format specifications, printf interprets the following extensions:

• %b 🔤 causes printf to expand backslash escape sequences in the corresponding argument in the same way as echo -e.
• %q 📋 causes printf to output the corresponding argument in a format that can be reused as shell input.
• %(datefmt)T 📅 causes printf to output the date-time string resulting from using datefmt as a format string for strftime(3). The corresponding argument is an integer representing the number of seconds since the epoch. Two special argument values may be used: -1 represents the current time, and -2 represents the time the shell was invoked. If no argument is specified, conversion behaves as if -1 had been given. This is an exception to the usual printf behavior.

The %b, %q, and %T directives all use the field width and precision arguments from the format specification and write that many bytes from (or use that wide a field for) the expanded argument, which usually contains more characters than the original.

Arguments to non-string format specifiers are treated as C constants, except that a leading plus or minus sign is allowed, and if the leading character is a single or double quote, the value is the ASCII value of the following character.

The format is reused as necessary to consume all of the arguments. If the format requires more arguments than are supplied, the extra format specifications behave as if a zero value or null string, as appropriate, had been supplied. The return value is zero on success, non-zero on failure.

pushd 📥 Add directory to stack

pushd [-n] [+n] [-n]
pushd [-n] [dir]

Adds a directory to the top of the directory stack, or rotates the stack, making the new top of the stack the current working directory. With no arguments, pushd exchanges the top two directories and returns 0, unless the directory stack is empty. Arguments, if supplied, have the following meanings:

• -n 🚫 Suppresses the normal change of directory when rotating or adding directories to the stack, so that only the stack is manipulated.
• +n ➡️ Rotates the stack so that the nth directory (counting from the left of the list shown by dirs, starting with zero) is at the top.
• -n ⬅️ Rotates the stack so that the nth directory (counting from the right of the list shown by dirs, starting with zero) is at the top.
• dir 📁 Adds dir to the directory stack at the top, making it the new current working directory as if it had been supplied as the argument to the cd builtin.

If the pushd command is successful, a dirs is performed as well. If the first form is used, pushd returns 0 unless the cd to dir fails. With the second form, pushd returns 0 unless the directory stack is empty, a non-existent directory stack element is specified, or the directory change to the specified new current directory fails.

pwd 📍 Print working directory

pwd [-LP]

Print the absolute pathname of the current working directory. The pathname printed contains no symbolic links if the -P option is supplied or the -o physical option to the set builtin command is enabled. If the -L option is used, the pathname printed may contain symbolic links. The return status is 0 unless an error occurs while reading the name of the current directory or an invalid option is supplied.

read 📖 Read input line

read [-ers] [-a aname] [-d delim] [-i text] [-n nchars] [-N nchars] [-p prompt] [-t timeout] [-u fd] [name ...]

One line is read from the standard input, or from the file descriptor fd supplied as an argument to the -u option, split into words as described above under Word Splitting, and the first word is assigned to the first name, the second word to the second name, and so on. If there are more words than names, the remaining words and their intervening delimiters are assigned to the last name. If there are fewer words read from the input stream than names, the remaining names are assigned empty values. The characters in IFS are used to split the line into words using the same rules the shell uses for expansion (described above under Word Splitting). The backslash character (\) may be used to remove any special meaning for the next character read and for line continuation. Options, if supplied, have the following meanings:

• -a aname 📦 The words are assigned to sequential indices of the array variable aname, starting at 0. aname is unset before any new values are assigned. Other name arguments are ignored.
• -d delim 🔤 The first character of delim is used to terminate the input line, rather than newline. If delim is the empty string, read will terminate a line when it reads a NUL character.
• -e ⌨️ If the standard input is coming from a terminal, readline (see READLINE above) is used to obtain the line. Readline uses the current (or default, if line editing was not previously active) editing settings, but uses Readline's default filename completion.
• -i text 📝 If readline is being used to read the line, text is placed into the editing buffer before editing begins.
• -n nchars 🔢 read returns after reading nchars characters rather than waiting for a complete line of input, but honors a delimiter if fewer than nchars characters are read before the delimiter.
• -N nchars 🔢 read returns after reading exactly nchars characters rather than waiting for a complete line of input, unless EOF is encountered or read times out. Delimiter characters encountered in the input are not treated specially and do not cause read to return until nchars characters are read. The result is not split on the characters in IFS; the intent is that the variable is assigned exactly the characters read (with the exception of backslash; see the -r option below).
• -p prompt 💬 Display prompt on standard error, without a trailing newline, before attempting to read any input. The prompt is displayed only if input is coming from a terminal.
• -r 🚫 Backslash does not act as an escape character. The backslash is considered to be part of the line. In particular, a backslash-newline pair may not then be used as a line continuation.
• -s 🤫 Silent mode. If input is coming from a terminal, characters are not echoed.
• -t timeout ⏱️ Cause read to time out and return failure if a complete line of input (or a specified number of characters) is not read within timeout seconds. timeout may be a decimal number with a fractional portion following the decimal point. This option is only effective if read is reading input from a terminal, pipe, or other special file; it has no effect when reading from regular files. If read times out, read saves any partial input read into the specified variable name. If timeout is 0, read returns immediately, without trying to read any data. The exit status is 0 if input is available on the specified file descriptor, non-zero otherwise. The exit status is greater than 128 if the timeout is exceeded.
• -u fd 📂 Read input from file descriptor fd.

If no names are supplied, the line read, without the ending delimiter but otherwise unmodified, is assigned to the variable REPLY. The exit status is zero, unless end-of-file is encountered, read times out (in which case the status is greater than 128), a variable assignment error (such as assigning to a readonly variable) occurs, or an invalid file descriptor is supplied as the argument to -u.

readonly 🔒 Mark variables as readonly

readonly [-aAf] [-p] [name[=word] ...]

The given names are marked readonly; the values of these names may not be changed by subsequent assignment. If the -f option is supplied, the functions corresponding to the names are so marked. The -a option restricts the variables to indexed arrays; the -A option restricts the variables to associative arrays. If both options are supplied, -A takes precedence. If no name arguments are given, or if the -p option is supplied, a list of all readonly names is printed. The other options may be used to restrict the output to a subset of the set of readonly names. The -p option causes output to be displayed in a format that may be reused as input. If a variable name is followed by =word, the value of the variable is set to word. The return status is 0 unless an invalid option is encountered, one of the names is not a valid shell variable name, or -f is supplied with a name that is not a function.

return 🔙 Return from function/script

return [n]

Causes a function to stop executing and return the value specified by n to its caller. If n is omitted, the return status is that of the last command executed in the function body. If return is executed by a trap handler, the last command used to determine the status is the last command executed before the trap handler. If return is executed during a DEBUG trap, the last command used to determine the status is the last command executed by the trap handler before return was invoked. If return is used outside a function, but during execution of a script by the . (source) command, it causes the shell to stop executing that script and return either n or the exit status of the last command executed within the script as the exit status of the script. If n is supplied, the return value is its least significant 8 bits. The return status is non-zero if return is supplied a non-numeric argument, or is used outside a function and not during execution of a script by . or source. Any command associated with the RETURN trap is executed before execution resumes after the function or script.

set ⚙️ Set/unset shell options and positional parameters

set [--abefhkmnptuvxBCEHPT] [-o option-name] [arg ...]
set [+abefhkmnptuvxBCEHPT] [+o option-name] [arg ...]

Without options, the name and value of each shell variable are displayed in a format that can be reused as input for setting or resetting the currently-set variables. Read-only variables cannot be reset. In posix mode, only shell variables are listed. The output is sorted according to the current locale. When options are specified, they set or unset shell attributes. Any arguments remaining after option processing are treated as values for the positional parameters and are assigned, in order, to $1, $2, ... $n. Options, if specified, have the following meanings:

• -a 📤 Each variable or function that is created or modified is given the export attribute and marked for export to the environment of subsequent commands.
• -b 🔔 Report the status of terminated background jobs immediately, rather than before the next primary prompt. This is effective only when job control is enabled.
• -e 🚫 Exit immediately if a pipeline (which may consist of a single simple command), a list, or a compound command (see SHELL GRAMMAR above), exits with a non-zero status. The shell does not exit if the command that fails is part of the command list immediately following a while or until keyword, part of the test following the if or elif reserved words, part of any command executed in a && or || list except the command following the final && or ||, any command in a pipeline but the last, or if the command's return value is being inverted with !. If a compound command other than a subshell returns a non-zero status because a command failed while -e was being ignored, the shell does not exit. A trap on ERR, if set, is executed before the shell exits. This option applies to the shell environment and each subshell environment separately (see COMMAND EXECUTION ENVIRONMENT above), and may cause subshells to exit before executing all the commands in the subshell.
• If a compound command or shell function executes in a context where -e is being ignored, none of the commands executed within the compound command or function body will be affected by the -e setting, even if -e is set and a command returns a failure status. If a compound command or shell function sets -e while executing in a context where -e is ignored, that setting will not have any effect until the compound command or the command containing the function call completes.
• -f 🚫 Disable pathname expansion.
• -h 🔍 Remember the location of commands as they are looked up for execution. This is enabled by default.
• -k 📋 All arguments in the form of assignment statements are placed in the environment for a command, not just those that precede the command name.
• -m 🖥️ Monitor mode. Job control is enabled. This option is on by default for interactive shells on systems that support it (see JOB CONTROL above). All processes run in a separate process group. When a background job completes, the shell prints a line containing its exit status.
• -n 📖 Read commands but do not execute them. This may be used to check a shell script for syntax errors. This is ignored by interactive shells.
• -o option-name ⚙️ The option-name can be one of the following:
  • allexport — Same as -a.
  • braceexpand — Same as -B.
  • emacs — Use an emacs-style command line editing interface. This is enabled by default when the shell is interactive, unless the shell is started with the --noediting option. This also affects the editing interface used for read -e.
  • errexit — Same as -e.
  • errtrace — Same as -E.
  • functrace — Same as -T.
  • hashall — Same as -h.
  • histexpand — Same as -H.
  • history — Enable command history, as described above under HISTORY. This option is on by default in interactive shells.
  • ignoreeof — The effect is as if the shell command IGNOREEOF=10 had been executed (see Shell Variables above).
  • keyword — Same as -k.
  • monitor — Same as -m.
  • noclobber — Same as -C.
  • noexec — Same as -n.
  • noglob — Same as -f.
  • nolog — Currently ignored.
  • notify — Same as -b.
  • nounset — Same as -u.
  • onecmd — Same as -t.
  • physical — Same as -P.
  • pipefail — If set, the return value of a pipeline is the value of the last (rightmost) command to exit with a non-zero status, or zero if all commands in the pipeline exit successfully. This option is disabled by default.
  • posix — Change the behavior of bash where the default operation differs from the POSIX standard to match the standard (posix mode). See SEE ALSO below for a reference to a document that details how posix mode affects bash's behavior.
  • privileged — Same as -p.
  • verbose — Same as -v.
  • vi — Use a vi-style command line editing interface. This also affects the editing interface used for read -e.
  • xtrace — Same as -x.
  If -o is supplied with no option-name, the values of the current options are printed. If +o is supplied with no option-name, a series of set commands to recreate the current option settings is displayed on the standard output.
• -p 🔐 Turn on privileged mode. In this mode, the $ENV and $BASH_ENV files are not processed, shell functions are not inherited from the environment, and the SHELLOPTS, BASHOPTS, CDPATH, and GLOBIGNORE variables, if they appear in the environment, are ignored. If the shell is started with the effective user (group) id not equal to the real user (group) id, and the -p option is not supplied, these actions are taken and the effective user id is set to the real user id. If the -p option is supplied at startup, the effective user id is not reset. Turning this option off causes the effective user and group ids to be set to the real user and group ids.
• -t ⏹️ Exit after reading and executing one command.
• -u ⚠️ Treat unset variables and parameters other than the special parameters "@" and "*" as an error when performing parameter expansion. If expansion is attempted on an unset variable or parameter, the shell prints an error message, and, if not interactive, exits with a non-zero status.
• -v 📖 Print shell input lines as they are read.
• -x 🔍 After expanding each simple command, for command, case command, select command, or arithmetic for command, display the expanded value of PS4, followed by the command and its expanded arguments or associated word list.
• -B 🔄 The shell performs brace expansion (see Brace Expansion above). This is on by default.
• -C 🚫 If set, bash does not overwrite an existing file with the >, >&, and <> redirection operators. This may be overridden when creating output files by using the redirection operator >| instead of >.
• -E 🔄 If set, any trap on ERR is inherited by shell functions, command substitutions, and commands executed in a subshell environment. The ERR trap is normally not inherited in such cases.
• -H 🔄 Enable ! style history substitution. This option is on by default when the shell is interactive.
• -P 🚫 If set, the shell does not resolve symbolic links when executing commands such as cd that change the current working directory. It uses the physical directory structure instead. By default, bash follows the logical chain of directories when performing commands which change the current directory.
• -T 🔄 If set, any traps on DEBUG and RETURN are inherited by shell functions, command substitutions, and commands executed in a subshell environment. The DEBUG and RETURN traps are normally not inherited in such cases.
• -- 🛑 If no arguments follow this option, then the positional parameters are unset. Otherwise, the positional parameters are set to the args, even if some of them begin with a -.
• - 🛑 Signal the end of options, cause all remaining args to be assigned to the positional parameters. The -x and -v options are turned off. If there are no args, the positional parameters remain unchanged.

The options are off by default unless otherwise noted. Using + rather than - causes these options to be turned off. The options can also be specified as arguments to an invocation of the shell. The current set of options may be found in $-. The return status is always true unless an invalid option is encountered.

shift ⬅️ Shift positional parameters

shift [n]

The positional parameters from n+1 ... are renamed to $1 .... Parameters represented by the numbers $# down to $#-n+1 are unset. n must be a non-negative number less than or equal to $#. If n is 0, no parameters are changed. If n is not given, it is assumed to be 1. If n is greater than $#, the positional parameters are not changed. The return status is greater than zero if n is greater than $# or less than zero; otherwise 0.

shopt ⚙️ Toggle shell options

shopt [-pqsu] [-o] [optname ...]

Toggle the values of settings controlling optional shell behavior. The settings can be either those listed below, or, if the -o option is used, those available with the -o option to the set builtin command. With no options, or with the -p option, a list of all settable options is displayed, with an indication of whether or not each is set; if optnames are supplied, the output is restricted to those options. The -p option causes output to be displayed in a form that may be reused as input. Other options have the following meanings:

• -s ✅ Enable (set) each optname.
• -u ❌ Disable (unset) each optname.
• -q 🤫 Suppresses normal output (quiet mode); the return status indicates whether the optname is set or unset. If multiple optname arguments are given with -q, the return status is zero if all optnames are enabled; non-zero otherwise.
• -o ⚙️ Restricts the values of optname to be those defined for the -o option to the set builtin.

If either -s or -u is used with no optname arguments, shopt shows only those options which are set or unset, respectively. Unless otherwise noted, the shopt options are disabled (unset) by default.

The return status when listing options is zero if all optnames are enabled, non-zero otherwise. When setting or unsetting options, the return status is zero unless an optname is not a valid shell option.

The list of shopt options is:

• assoc_expand_once 🔄 If set, the shell suppresses multiple evaluation of associative array subscripts during arithmetic expression evaluation, while executing builtins that can perform variable assignments, and while executing builtins that perform array dereferencing.
• autocd 📁 If set, a command name that is the name of a directory is executed as if it were the argument to the cd command. This option is only used by interactive shells.
• cdable_vars 📁 If set, an argument to the cd builtin command that is not a directory is assumed to be the name of a variable whose value is the directory to change to.
• cdspell ✏️ If set, minor errors in the spelling of a directory component in a cd command will be corrected. The errors checked for are transposed characters, a missing character, and one character too many. If a correction is found, the corrected filename is printed, and the command proceeds. This option is only used by interactive shells.
• checkhash 🔍 If set, bash checks that a command found in the hash table exists before trying to execute it. If a hashed command no longer exists, a normal path search is performed.
• checkjobs 📋 If set, bash lists the status of any stopped and running jobs before exiting an interactive shell. If any jobs are running, this causes the exit to be deferred until a second exit is attempted without an intervening command (see JOB CONTROL above). The shell always postpones exiting if any jobs are stopped.
• checkwinsize 📐 If set, bash checks the window size after each external (non-builtin) command and, if necessary, updates the values of LINES and COLUMNS. This option is enabled by default.
• cmdhist 📜 If set, bash attempts to save all lines of a multiple-line command in the same history entry. This allows easy re-editing of multi-line commands. This option is enabled by default, but only has an effect if command history is enabled, as described above under HISTORY.
• compat31, compat32, compat40, compat41, compat42, compat43, compat44 🔄 These control aspects of the shell's compatibility mode (see SHELL COMPATIBILITY MODE below).
• complete_fullquote 📝 If set, bash quotes all shell metacharacters in filenames and directory names when performing completion. If not set, bash removes metacharacters such as the dollar sign from the set of characters that will be quoted in completed filenames when these metacharacters appear in shell variable references in words to be completed. This means that dollar signs in variable names that expand to directories will not be quoted; however, any dollar signs appearing in filenames will not be quoted, either. This is active only when bash is using backslashes to quote completed filenames. This variable is set by default, which is the default bash behavior in versions through 4.2.
• direxpand 📁 If set, bash replaces directory names with the results of word expansion when performing filename completion. This changes the contents of the readline editing buffer. If not set, bash attempts to preserve what the user typed.
• dirspell ✏️ If set, bash attempts spelling correction on directory names during word completion if the directory name initially supplied does not exist.
• dotglob 🔍 If set, bash includes filenames beginning with a . in the results of pathname expansion. The filenames . and .. must always be matched explicitly, even if dotglob is set.
• execfail 🚫 If set, a non-interactive shell will not exit if it cannot execute the file specified as an argument to the exec builtin command. An interactive shell does not exit if exec fails.
• expand_aliases 🔗 If set, aliases are expanded as described above under ALIASES. This option is enabled by default for interactive shells.
• extdebug 🐛 If set at shell invocation, or in a shell startup file, arrange to execute the debugger profile before the shell starts, identical to the --debugger option. If set after invocation, behavior intended for use by debuggers is enabled:
  1. The -F option to the declare builtin displays the source file name and line number corresponding to each function name supplied as an argument.
  2. If the command run by the DEBUG trap returns a non-zero value, the next command is skipped and not executed.
  3. If the command run by the DEBUG trap returns a value of 2, and the shell is executing in a subroutine (a shell function or a shell script executed by the . or source builtins), the shell simulates a call to return.
  4. BASH_ARGC and BASH_ARGV are updated as described in their descriptions above.
  5. Function tracing is enabled: command substitution, shell functions, and subshells invoked with ( command ) inherit the DEBUG and RETURN traps.
  6. Error tracing is enabled: command substitution, shell functions, and subshells invoked with ( command ) inherit the ERR trap.
• extglob 🔀 If set, the extended pattern matching features described above under Pathname Expansion are enabled.
• extquote 📝 If set, $'string' and $"string" quoting is performed within ${parameter} expansions enclosed in double quotes. This option is enabled by default.
• failglob ❌ If set, patterns which fail to match filenames during pathname expansion result in an expansion error.
• force_fignore 🚫 If set, the suffixes specified by the FIGNORE shell variable cause words to be ignored when performing word completion even if the ignored words are the only possible completions. See SHELL VARIABLES above for a description of FIGNORE. This option is enabled by default.
• globasciiranges 🔤 If set, range expressions used in pattern matching bracket expressions (see Pattern Matching above) behave as if in the traditional C locale when performing comparisons. That is, the current locale's collating sequence is not taken into account, so b will not collate between A and B, and upper-case and lower-case ASCII characters will collate together.
• globstar ** 🌟 If set, the pattern ** used in a pathname expansion context will match all files and zero or more directories and subdirectories. If the pattern is followed by a /, only directories and subdirectories match.
• gnu_errfmt 📝 If set, shell error messages are written in the standard GNU error message format.
• histappend ➕ If set, the history list is appended to the file named by the value of the HISTFILE variable when the shell exits, rather than overwriting the file.
• histreedit 🔄 If set, and readline is being used, a user is given the opportunity to re-edit a failed history substitution.
• histverify 🔄 If set, and readline is being used, the results of history substitution are not immediately passed to the shell parser. Instead, the resulting line is loaded into the readline editing buffer, allowing further modification.
• hostcomplete 🌐 If set, and readline is being used, bash will attempt to perform hostname completion when a word containing @ is being completed (see Completing under READLINE above). This is enabled by default.
• huponexit 🚪 If set, bash will send SIGHUP to all jobs when an interactive login shell exits.
• inherit_errexit 🔄 If set, command substitution inherits the value of the errexit option, instead of unsetting it in the subshell environment. This option is enabled when posix mode is enabled.
• interactive_comments 💬 If set, allow a word beginning with # to cause that word and all remaining characters on that line to be ignored in an interactive shell (see COMMENTS above). This option is enabled by default.
• lastpipe 🔄 If set, and job control is not active, the shell runs the last command of a pipeline not executed in the background in the current shell environment.
• lithist 📜 If set, and the cmdhist option is enabled, multi-line commands are saved to the history with embedded newlines rather than using semicolon separators where possible.
• localvar_inherit 📍 If set, local variables inherit the value and attributes of a variable of the same name that exists at a previous scope before any new value is assigned. The nameref attribute is not inherited.
• localvar_unset 📍 If set, calling unset on local variables in previous function scopes marks them so subsequent lookups find them unset until that function returns. This is identical to the behavior of unsetting local variables at the current function scope.
• login_shell 🔐 The shell sets this option if it is started as a login shell (see INVOCATION above). The value may not be changed.
• mailwarn 📧 If set, and a file that bash is checking for mail has been accessed since the last time it was checked, the message "The mail in mailfile has been read" is displayed.
• no_empty_cmd_completion 🚫 If set, and readline is being used, bash will not attempt to search the PATH for possible completions when completion is attempted on an empty line.
• nocaseglob 🔤 If set, bash matches filenames in a case-insensitive fashion when performing pathname expansion (see Pathname Expansion above).
• nocasematch 🔤 If set, bash matches patterns in a case-insensitive fashion when performing matching while executing case or [[ conditional commands, when performing pattern substitution word expansions, or when filtering possible completions as part of programmable completion.
• nullglob ❌ If set, bash allows patterns which match no files (see Pathname Expansion above) to expand to a null string, rather than themselves.
• progcomp ✅ If set, the programmable completion facilities (see Programmable Completion above) are enabled. This option is enabled by default.
• progcomp_alias 🔗 If set, and programmable completion is enabled, bash treats a command name that doesn't have any completions as a possible alias and attempts alias expansion. If it has an alias, bash attempts programmable completion using the command word resulting from the expanded alias.
• promptvars 💬 If set, prompt strings undergo parameter expansion, command substitution, arithmetic expansion, and quote removal after being expanded as described in PROMPTING above. This option is enabled by default.
• restricted_shell 🔒 The shell sets this option if it is started in restricted mode (see RESTRICTED SHELL below). The value may not be changed. This is not reset when the startup files are executed, allowing the startup files to discover whether or not a shell is restricted.
• shift_verbose 📢 If set, the shift builtin prints an error message when the shift count exceeds the number of positional parameters.
• sourcepath 📂 If set, the source (.) builtin uses the value of PATH to find the directory containing the file supplied as an argument. This option is enabled by default.
• xpg_echo 🔊 If set, the echo builtin expands backslash-escape sequences by default.

suspend ⏸️ Suspend shell execution

suspend [-f]

Suspend the execution of this shell until it receives a SIGCONT signal. A login shell cannot be suspended; the -f option can be used to override this and force the suspension. The return status is 0 unless the shell is a login shell and -f is not supplied, or if job control is not enabled.

test / [ ❓ Evaluate conditional expression

test expr
[ expr ]

Return a status of 0 (true) or 1 (false) depending on the evaluation of the conditional expression expr. Each operator and operand must be a separate argument. Expressions are composed of the primaries described above under CONDITIONAL EXPRESSIONS. test does not accept any options, nor does it accept and ignore an argument of -- as signifying the end of options.

Expressions may be combined using the following operators, listed in decreasing order of precedence. The evaluation depends on the number of arguments; see below. Operator precedence is used when there are five or more arguments.

• ! expr ❌ True if expr is false.
• ( expr ) 🔢 Returns the value of expr. This may be used to override the normal precedence of operators.
• expr1 -a expr2 ✅ True if both expr1 and expr2 are true.
• expr1 -o expr2 ✅ True if either expr1 or expr2 is true.

test and [ evaluate conditional expressions using a set of rules based on the number of arguments.

• 0 arguments: The expression is false.
• 1 argument: The expression is true if and only if the argument is not null.
• 2 arguments: If the first argument is !, the expression is true if and only if the second argument is null. If the first argument is one of the unary conditional operators listed above under CONDITIONAL EXPRESSIONS, the expression is true if the unary test is true. If the first argument is not a valid unary conditional operator, the expression is false.
• 3 arguments: The following conditions are applied in the order listed. If the second argument is one of the binary conditional operators listed above under CONDITIONAL EXPRESSIONS, the result of the expression is the result of the binary test using the first and third arguments as operands. The -a and -o operators are considered binary operators when there are three arguments. If the first argument is !, the value is the negation of the two-argument test using the second and third arguments. If the first argument is exactly ( and the third argument is exactly ), the result is the one-argument test of the second argument. Otherwise, the expression is false.
• 4 arguments: If the first argument is !, the result is the negation of the three-argument expression composed of the remaining arguments. Otherwise, the expression is parsed and evaluated according to precedence using the rules listed above.
• 5 or more arguments: The expression is parsed and evaluated according to precedence using the rules listed above.

When used with test or [, the < and > operators sort lexicographically using ASCII ordering.

times ⏱️ Print accumulated times

times — Print the accumulated user and system times for the shell and for processes run from the shell. The return status is 0.

trap ⚠️ Set signal/event handlers

trap [-lp] [[arg] sigspec ...]

The command arg is to be read and executed when the shell receives signal(s) sigspec. If arg is absent (and there is a single sigspec) or -, each specified signal is reset to its original disposition (the value it had upon entrance to the shell). If arg is the null string the signal specified by each sigspec is ignored by the shell and by the commands it invokes. If arg is not present and -p has been supplied, then the trap commands associated with each sigspec are displayed. If no arguments are supplied or if only -p is given, trap prints the list of commands associated with each signal. The -l option causes the shell to print a list of signal names and their corresponding numbers. Each sigspec is either a signal name defined in <signal.h>, or a signal number. Signal names are case insensitive and the SIG prefix is optional.

If a sigspec is EXIT (0) the command arg is executed on exit from the shell. If a sigspec is DEBUG, the command arg is executed before every simple command, for command, case command, select command, every arithmetic for command, and before the first command executes in a shell function (see SHELL GRAMMAR above). Refer to the description of the extdebug option to the shopt builtin for details of its effect on the DEBUG trap. If a sigspec is RETURN, the command arg is executed each time a shell function or a script executed with the . or source builtins finishes executing.

If a sigspec is ERR, the command arg is executed whenever a pipeline (which may consist of a single simple command), a list, or a compound command returns a non-zero exit status, subject to the following conditions. The ERR trap is not executed if the failed command is part of the command list immediately following a while or until keyword, part of the test in an if statement, part of a command executed in a && or || list except the command following the final && or ||, any command in a pipeline but the last, or if the command's return value is being inverted using !. These are the same conditions obeyed by the errexit (-e) option.

Signals ignored upon entry to the shell cannot be trapped or reset. Trapped signals that are not being ignored are reset to their original values in a subshell or subshell environment when one is created. The return status is false if any sigspec is invalid; otherwise trap returns true.

type 🔍 Indicate how name would be interpreted

type [-aftpP] name [name ...]

With no options, indicate how each name would be interpreted if used as a command name. If the -t option is used, type prints a string which is one of alias, keyword, function, builtin, or file if name is an alias, shell reserved word, function, builtin, or disk file, respectively. If the name is not found, then nothing is printed, and an exit status of false is returned. If the -p option is used, type either returns the name of the disk file that would be executed if name were specified as a command name, or nothing if type -t name would not return file. The -P option forces a PATH search for each name, even if type -t name would not return file. If a command is hashed, -p and -P print the hashed value, which is not necessarily the file that appears first in PATH. If the -a option is used, type prints all of the places that contain an executable named name. This includes aliases and functions, if and only if the -p option is not also used. The table of hashed commands is not consulted when using -a. The -f option suppresses shell function lookup, as with the command builtin. type returns true if all of the arguments are found, false if any are not found.

ulimit 📊 Set/get resource limits

ulimit [-HS] -a
ulimit [-HS] [-bcdefiklmnpqrstuvxPRT [limit]]

Provides control over the resources available to the shell and to processes started by it, on systems that allow such control. The -H and -S options specify that the hard or soft limit is set for the given resource. A hard limit cannot be increased by a non-root user once it is set; a soft limit may be increased up to the value of the hard limit. If neither -H nor -S is specified, both the soft and hard limits are set. The value of limit can be a number in the unit specified for the resource or one of the special values hard, soft, or unlimited, which stand for the current hard limit, the current soft limit, and no limit, respectively. If limit is omitted, the current value of the soft limit of the resource is printed, unless the -H option is given. When more than one resource is specified, the limit name and unit, if appropriate, are printed before the value. Other options are interpreted as follows:

• -a 📋 All current limits are reported; no limits are set
• -b 📦 The maximum socket buffer size
• -c 📄 The maximum size of core files created
• -d 📦 The maximum size of a process's data segment
• -e ⏱️ The maximum scheduling priority ("nice")
• -f 📄 The maximum size of files written by the shell and its children
• -i 🔢 The maximum number of pending signals
• -k 🔢 The maximum number of kqueues that may be allocated
• -l 📦 The maximum size that may be locked into memory
• -m 📦 The maximum resident set size (many systems do not honor this limit)
• -n 🔢 The maximum number of open file descriptors (most systems do not allow this value to be set)
• -p 📄 The pipe size in 512-byte blocks (this may not be set)
• -q 📦 The maximum number of bytes in POSIX message queues
• -r ⏱️ The maximum real-time scheduling priority
• -s 📦 The maximum stack size
• -t ⏱️ The maximum amount of cpu time in seconds
• -u 🔢 The maximum number of processes available to a single user
• -v 📦 The maximum amount of virtual memory available to the shell and, on some systems, to its children
• -x 🔢 The maximum number of file locks
• -P 🔢 The maximum number of pseudoterminals
• -R ⏱️ The maximum time a real-time process can run before blocking, in microseconds
• -T 🔢 The maximum number of threads

If limit is given, and the -a option is not used, limit is the new value of the specified resource. If no option is given, then -f is assumed. Values are in 1024-byte increments, except for -t, which is in seconds; -R, which is in microseconds; -p, which is in units of 512-byte blocks; -P, -T, -b, -k, -n, and -u, which are unscaled values; and, when in posix mode, -c and -f, which are in 512-byte increments. The return status is 0 unless an invalid option or argument is supplied, or an error occurs while setting a new limit.

umask 🔒 Set file creation mask

umask [-p] [-S] [mode]

The user file-creation mask is set to mode. If mode begins with a digit, it is interpreted as an octal number; otherwise it is interpreted as a symbolic mode mask similar to that accepted by chmod(1). If mode is omitted, the current value of the mask is printed. The -S option causes the mask to be printed in symbolic form; the default output is an octal number. If the -p option is supplied, and mode is omitted, the output is in a form that may be reused as input. The return status is 0 if the mode was successfully changed or if no mode argument was supplied, and false otherwise.

unalias ❌ Remove alias

unalias [-a] [name ...]

Remove each name from the list of defined aliases. If -a is supplied, all alias definitions are removed. The return value is true unless a supplied name is not a defined alias.

unset ❌ Unset variables/functions

unset [-fv] [-n] [name ...]

For each name, remove the corresponding variable or function. If the -v option is given, each name refers to a shell variable, and that variable is removed. Read-only variables may not be unset. If -f is specified, each name refers to a shell function, and the function definition is removed. If the -n option is supplied, and name is a variable with the nameref attribute, name will be unset rather than the variable it references. -n has no effect if the -f option is supplied. If no options are supplied, each name refers to a variable; if there is no variable by that name, a function with that name, if any, is unset. Each unset variable or function is removed from the environment passed to subsequent commands. If any of BASH_ALIASES, BASH_ARGV0, BASH_CMDS, BASH_COMMAND, BASH_SUBSHELL, BASHPID, COMP_WORDBREAKS, DIRSTACK, EPOCHREALTIME, EPOCHSECONDS, FUNCNAME, GROUPS, HISTCMD, LINENO, RANDOM, SECONDS, or SRANDOM are unset, they lose their special properties, even if they are subsequently reset. The exit status is true unless a name is readonly.

wait ⏳ Wait for background processes

wait [-fn] [-p varname] [id ...]

Wait for each specified child process and return its termination status. Each id may be a process ID or a job specification; if a job spec is given, all processes in that job's pipeline are waited for. If id is not given, wait waits for all running background jobs and the last-executed process substitution, if its process id is the same as $!, and the return status is zero. If the -n option is supplied, wait waits for a single job from the list of ids or, if no ids are supplied, any job, to complete and returns its exit status. If none of the supplied arguments is a child of the shell, or if no arguments are supplied and the shell has no unwaited-for children, the exit status is 127. If the -p option is supplied, the process or job identifier of the job for which the exit status is returned is assigned to the variable varname named by the option argument. The variable will be unset initially, before any assignment. This is useful only when the -n option is supplied. Supplying the -f option, when job control is enabled, forces wait to wait for id to terminate before returning its status, instead of returning when it changes status. If id specifies a non-existent process or job, the return status is 127. Otherwise, the return status is the exit status of the last process or job waited for.

🔄 Shell Compatibility Mode

Bash-4.0 introduced the concept of a shell compatibility level, specified as a set of options to the shopt builtin: compat31, compat32, compat40, compat41, and so on. There is only one current compatibility level – each option is mutually exclusive. The compatibility level is intended to allow users to select behavior from previous versions that is incompatible with newer versions while they migrate scripts to use current features and behavior. It's intended to be a temporary solution.

This section does not mention behavior that is standard for a particular version (e.g., setting compat32 means that quoting the rhs of the regexp matching operator quotes special regexp characters in the word, which is default behavior in bash-3.2 and above).

If a user enables, say, compat32, it may affect the behavior of other compatibility levels up to and including the current compatibility level. The idea is that each compatibility level controls behavior that changed in that version of bash, but that behavior may have been present in earlier versions. For instance, the change to use locale-based comparisons with the [[ command came in bash-4.1, and earlier versions used ASCII-based comparisons, so enabling compat32 will enable ASCII-based comparisons as well. That granularity may not be sufficient for all uses, and as a result users should employ compatibility levels carefully. Read the documentation for a particular feature to find out the current behavior.

Bash-4.3 introduced a new shell variable: BASH_COMPAT. The value assigned to this variable (a decimal version number like 4.2, or an integer corresponding to the compatNN option, like 42) determines the compatibility level.

Starting with bash-4.4, Bash has begun deprecating older compatibility levels. Eventually, the options will be removed in favor of BASH_COMPAT.

Bash-5.0 is the final version for which there will be an individual shopt option for the previous version. Users should use BASH_COMPAT on bash-5.0 and later versions.

The following table describes the behavior changes controlled by each compatibility level setting. The compatNN tag is used as shorthand for setting the compatibility level to NN using one of the following mechanisms. For versions prior to bash-5.0, the compatibility level may be set using the corresponding compatNN shopt option. For bash-4.3 and later versions, the BASH_COMPAT variable is preferred, and it is required for bash-5.1 and later versions.

⚙️ compat31

• 🔹 quoting the rhs of the [[ command's regexp matching operator (=~) has no special effect

⚙️ compat32

• 🔹 interrupting a command list such as a ; b ; c causes the execution of the next command in the list (in bash-4.0 and later versions, the shell acts as if it received the interrupt, so interrupting one command in a list aborts the execution of the entire list)

⚙️ compat40

• 🔹 the < and > operators to the [[ command do not consider the current locale when comparing strings; they use ASCII ordering. Bash versions prior to bash-4.1 use ASCII collation and strcmp(3); bash-4.1 and later use the current locale's collation sequence and strcoll(3).

⚙️ compat41

• 🔹 in posix mode, time may be followed by options and still be recognized as a reserved word (this is POSIX interpretation 267)
• 🔹 in posix mode, the parser requires that an even number of single quotes occur in the word portion of a double-quoted parameter expansion and treats them specially, so that characters within the single quotes are considered quoted (this is POSIX interpretation 221)

⚙️ compat42

• 🔹 the replacement string in double-quoted pattern substitution does not undergo quote removal, as it does in versions after bash-4.2
• 🔹 in posix mode, single quotes are considered special when expanding the word portion of a double-quoted parameter expansion and can be used to quote a closing brace or other special character (this is part of POSIX interpretation 221); in later versions, single quotes are not special within double-quoted word expansions

⚙️ compat43

• 🔹 the shell does not print a warning message if an attempt is made to use a quoted compound assignment as an argument to declare (declare -a foo='(1 2)'). Later versions warn that this usage is deprecated
• 🔹 word expansion errors are considered non-fatal errors that cause the current command to fail, even in posix mode (the default behavior is to make them fatal errors that cause the shell to exit)
• 🔹 when executing a shell function, the loop state (while/until/etc.) is not reset, so break or continue in that function will break or continue loops in the calling context. Bash-4.4 and later reset the loop state to prevent this

⚙️ compat44

• 🔹 the shell sets up the values used by BASH_ARGV and BASH_ARGC so they can expand to the shell's positional parameters even if extended debugging mode is not enabled
• 🔹 a subshell inherits loops from its parent context, so break or continue will cause the subshell to exit. Bash-5.0 and later reset the loop state to prevent the exit
• 🔹 variable assignments preceding builtins like export and readonly that set attributes continue to affect variables with the same name in the calling environment even if the shell is not in posix mode

⚙️ compat50

• 🔹 Bash-5.1 changed the way $RANDOM is generated to introduce slightly more randomness. If the shell compatibility level is set to 50 or lower, it reverts to the method from bash-5.0 and previous versions, so seeding the random number generator by assigning a value to RANDOM will produce the same sequence as in bash-5.0
• 🔹 If the command hash table is empty, bash versions prior to bash-5.1 printed an informational message to that effect, even when producing output that can be reused as input. Bash-5.1 suppresses that message when the -l option is supplied.

🚫 RESTRICTED SHELL

If bash is started with the name rbash, or the -r option is supplied at invocation, the shell becomes restricted. A restricted shell is used to set up an environment more controlled than the standard shell. It behaves identically to bash with the exception that the following are disallowed or not performed:

• 🔴 changing directories with cd
• 🔴 setting or unsetting the values of SHELL, PATH, HISTFILE, ENV, or BASH_ENV
• 🔴 specifying command names containing /
• 🔴 specifying a filename containing a / as an argument to the . builtin command
• 🔴 specifying a filename containing a slash as an argument to the history builtin command
• 🔴 specifying a filename containing a slash as an argument to the -p option to the hash builtin command
• 🔴 importing function definitions from the shell environment at startup
• 🔴 parsing the value of SHELLOPTS from the shell environment at startup
• 🔴 redirecting output using the >, >|, <>, >&, &>, and >> redirection operators
• 🔴 using the exec builtin command to replace the shell with another command
• 🔴 adding or deleting builtin commands with the -f and -d options to the enable builtin command
• 🔴 using the enable builtin command to enable disabled shell builtins
• 🔴 specifying the -p option to the command builtin command
• 🔴 turning off restricted mode with set +r or set +o restricted.

These restrictions are enforced after any startup files are read.

When a command that is found to be a shell script is executed (see COMMAND EXECUTION above), rbash turns off any restrictions in the shell spawned to execute the script.

📚 SEE ALSO

• 📖 Bash Reference Manual, Brian Fox and Chet Ramey
• 📖 The Gnu Readline Library, Brian Fox and Chet Ramey
• 📖 The Gnu History Library, Brian Fox and Chet Ramey
• 📋 Portable Operating System Interface (POSIX) Part 2: Shell and Utilities, IEEE — http://pubs.opengroup.org/onlinepubs/9699919799/
• 🔗 http://tiswww.case.edu/~chet/bash/POSIX — a description of POSIX mode
• 📘 sh(1), ksh(1), csh(1)
• 📘 emacs(1), vi(1)
• 📘 readline(3)

📁 FILES

• /bin/bash — 🚀 The bash executable
• /etc/profile — ⚙️ The systemwide initialization file, executed for login shells
• /etc/bash.bashrc — ⚙️ The systemwide per-interactive-shell startup file
• /etc/bash.bash.logout — 🧹 The systemwide login shell cleanup file, executed when a login shell exits
• ~/.bash_profile — 👤 The personal initialization file, executed for login shells
• ~/.bashrc — 👤 The individual per-interactive-shell startup file
• ~/.bash_logout — 🧹 The individual login shell cleanup file, executed when a login shell exits
• ~/.inputrc — ⌨️ Individual readline initialization file

👤 AUTHORS

• 👤 Brian Fox, Free Software Foundation
  bfox AT gnu.org
• 👤 Chet Ramey, Case Western Reserve University
  chet.ramey AT case.edu

The user wants me to enhance the BUG REPORTS section of the BASH man page with emojis while preserving the original structure and content. Let me analyze the input: 1. The section heading is "BUG REPORTS" - I need to convert this to

with an emoji prefix 2. There are paragraphs describing how to report bugs 3. There's a list of items that should include in bug reports - this should be a proper HTML list 4. There are links that need to be preserved 5. There are some code-like elements (bashbug command, email addresses, URL) that should be in tags Let me transform this: - Section heading:

🐛 Bug Reports

- Keep paragraphs - Convert the "ALL bug reports should include" list into a proper

- The items "The version number of bash", "The hardware and operating system", etc. need to be wrapped in where appropriate? Actually, these aren't really code - they're list items. The version number references though... Looking more carefully: - "bashbug" command - should be - "bug-bash AT gnu.org" - this is an email, preserve the original formatting - "chet.ramey AT case.edu" - email, preserve - The URL - preserve the Let me write the enhanced version:

🐛 Bug Reports

If you find a bug in bash, you should report it. But first, you should make sure that it really is a bug, and that it appears in the latest version of bash. The latest version is always available from ftp://ftp.gnu.org/pub/gnu/bash/.

Once you have determined that a bug actually exists, use the bashbug command to submit a bug report. If you have a fix, you are encouraged to mail that as well! Suggestions and `philosophical' bug reports may be mailed to bug-bash AT gnu.org or posted to the Usenet newsgroup gnu.bash.bug.

ALL bug reports should include:

• 📌 The version number of bash
• 💻 The hardware and operating system
• 🛠️ The compiler used to compile
• 📝 A description of the bug behaviour
• 🧪 A short script or `recipe' which exercises the bug

bashbug inserts the first three items automatically into the template it provides for filing a bug report.

Comments and bug reports concerning this manual page should be directed to chet.ramey AT case.edu.

Wait, let me re-check the rules: - Rule 10: Use standard
• or
  1. for ALL lists. Emoji may appear inside
  2. text content, but NEVER replace the list structure with emoji-only lines. ✓ I'm using
     with
     • and emojis inside - Rule 11: NEVER use emoji characters as visual bullet replacements at the start of paragraphs — always use proper HTML list tags. ✓ I'm starting with

       tags, not emoji bullets - Rule 12: For function, method, and class reference sections... This is NOT a function reference section, so I can use emojis in list items. - Rule 13: XSS prevention - check for any bare < or > outside allowed tags. The original has AT - that's part of the tag, so it's fine. The tags are allowed. Let me check the original HTML again carefully: - `ftp://ftp.gnu.org/pub/gnu/bash/` - this is fine - `bug-bash AT gnu.org` - inline inside is allowed - All other tags are allowed The original BUG REPORTS should become

       🐛 Bug Reports

       . The original uses for the heading. I need to convert to

       . Let me also think about adding emojis to make it scannable: - "the latest version of bash" - could add 🌐 or similar - "bashbug command" - 🔧 - "Suggestions and 'philosophical' bug reports" - 💭 - "Usenet newsgroup" - 📰 - "ALL bug reports should include" - keep but add ⚠️ - The list items - already have emojis Let me refine:

       🐛 Bug Reports

       If you find a bug in bash, you should report it. But first, you should make sure that it really is a bug, and that it appears in the latest version of bash. The latest version is always available from ftp://ftp.gnu.org/pub/gnu/bash/.

       Once you have determined that a bug actually exists, use the bashbug command to submit a bug report. If you have a fix, you are encouraged to mail that as well! 💡 Suggestions and `philosophical' bug reports may be mailed to bug-bash AT gnu.org or posted to the Usenet newsgroup gnu.bash.bug.

       ⚠️ ALL bug reports should include:

       • 📌 The version number of bash
       • 💻 The hardware and operating system
       • 🛠️ The compiler used to compile
       • 📝 A description of the bug behaviour
       • 🧪 A short script or `recipe' which exercises the bug

       The bashbug command inserts the first three items automatically into the template it provides for filing a bug report.

       📧 Comments and bug reports concerning this manual page should be directed to chet.ramey AT case.edu.

       Wait, I should avoid putting emojis right before paragraphs or as bullet replacements for lists. Let me re-read rule 11: "NEVER use emoji characters (🔹, 🔸, ▪️, ▫️, ➡️, 📌, 🟢) as visual bullet replacements at the start of paragraphs — always use proper HTML list tags." So I shouldn't start paragraphs with emoji. Let me adjust - I'll put the emoji inside the text or at the end, not at the start of paragraphs. Actually, looking again: "at the start of paragraphs" - so I shouldn't start paragraphs with emojis. Let me restructure:

       🐛 Bug Reports

       If you find a bug in bash, you should report it 📢. But first, you should make sure that it really is a bug, and that it appears in the latest version of bash. The latest version is always available from ftp://ftp.gnu.org/pub/gnu/bash/.

       Once you have determined that a bug actually exists, use the bashbug command to submit a bug report. If you have a fix, you are encouraged to mail that as well! Suggestions and `philosophical' bug reports may be mailed to bug-bash AT gnu.org or posted to the Usenet newsgroup gnu.bash.bug 💬.

       ⚠️ ALL bug reports should include:

       • 📌 The version number of bash
       • 💻 The hardware and operating system
       • 🛠️ The compiler used to compile
       • 📝 A description of the bug behaviour
       • 🧪 A short script or `recipe' which exercises the bug

       The bashbug command inserts the first three items automatically into the template it provides for filing a bug report.

       Comments and bug reports concerning this manual page should be directed to chet.ramey AT case.edu 📧.

       Hmm, the issue is the original has "ALL bug reports should include:" as just a paragraph - the emphasis is on "ALL". So I should keep that as a paragraph and then the list follows. Let me put the emoji at the end of the emphasis notice or use the to wrap "ALL" while still keeping the paragraph structure. Actually, the cleaner approach is to:

       ALL bug reports should include:

       and add the emoji inline. Let me think about this more carefully. Looking at rule 11 again: "NEVER use emoji characters (🔹, 🔸, ▪️, ▫️, ➡️, 📌, 🟢) as visual bullet replacements at the start of paragraphs". The listed emojis are specific bullet-like ones. ⚠️ is not in that list and is more of a warning indicator. But to be safe, I'll avoid leading the paragraph with emojis. Let me do this:

       🐛 Bug Reports

       If you find a bug in bash, you should report it. But first, you should make sure that it really is a bug, and that it appears in the latest version of bash. The latest version is always available from ftp://ftp.gnu.org/pub/gnu/bash/ 🌐.

       Once you have determined that a bug actually exists, use the bashbug command to submit a bug report 🔧. If you have a fix, you are encouraged to mail that as well! Suggestions and `philosophical' bug reports may be mailed to bug-bash AT gnu.org or posted to the Usenet newsgroup gnu.bash.bug 📰.

       Every bug report should include the following:

       • 📌 The version number of bash
       • 💻 The hardware and operating system
       • 🛠️ The compiler used to compile
       • 📝 A description of the bug behaviour
       • 🧪 A short script or `recipe' which exercises the bug

       The bashbug command inserts the first three items automatically into the template it provides for filing a bug report.

       Comments and bug reports concerning this manual page should be directed to chet.ramey AT case.edu 📧.

       Wait, I should preserve the original text more closely. The original says "ALL bug reports should include:" - I should keep that wording. Let me revise: Actually, the original "ALL" was likely uppercase for emphasis. I can preserve that. Let me finalize:

       🐛 Bug Reports

       If you find a bug in bash, you should report it. But first, you should make sure that it really is a bug, and that it appears in the latest version of bash. The latest version is always available from ftp://ftp.gnu.org/pub/gnu/bash/.

       Once you have determined that a bug actually exists, use the bashbug command to submit a bug report. If you have a fix, you are encouraged to mail that as well! Suggestions and `philosophical' bug reports may be mailed to bug-bash AT gnu.org or posted to the Usenet newsgroup gnu.bash.bug.

       Every bug report should include:

       • 📌 The version number of bash
       • 💻 The hardware and operating system
       • 🛠️ The compiler used to compile
       • 📝 A description of the bug behaviour
       • 🧪 A short script or `recipe' which exercises the bug

       The bashbug command inserts the first three items automatically into the template it provides for filing a bug report.

       Comments and bug reports concerning this manual page should be directed to chet.ramey AT case.edu.

       Hmm, but the original says "ALL bug reports should include:" - I should preserve that. Let me keep it close to original:

       ALL bug reports should include:

       Actually, the original document text is what we need to preserve. The "ALL" was uppercase in the original. Let me preserve that. Let me think about whether to add emojis to list items. Rule 12 says: "For function, method, and class reference sections... use
     • name(args) — description
     format WITHOUT per-item emoji." This is NOT a function reference section, so emojis per item are fine. Rule 10: "Emoji may appear inside
     • text content". So emojis in list items are OK. Let me also think about whether to add a Quick Reference section. Rule 21 says: "ALWAYS create a

       🚀 Quick Reference

       section as the second section (right after NAME)." But this is just ONE section of the man page (part 37 of 38). I'm only enhancing THE BUG REPORTS section. The instruction says "Only enhance THIS section. Do NOT wrap in //." So I should NOT add a Quick Reference section here - that's for the whole document, not a single section. Same for Exit Codes (rule 22) - not relevant for this section. Let me finalize my output. I want to: 1. Convert BUG REPORTS to

       🐛 Bug Reports

       2. Preserve all original text 3. Add emojis tastefully 4. Convert the list items to proper
       5. Wrap `bashbug` and `gnu.bash.bug` in tags 6. Preserve all and tags Final version:

       🐛 Bug Reports

       If you find a bug in bash, you should report it. But first, you should make sure that it really is a bug, and that it appears in the latest version of bash. The latest version is always available from ftp://ftp.gnu.org/pub/gnu/bash/.

       Once you have determined that a bug actually exists, use the bashbug command to submit a bug report. If you have a fix, you are encouraged to mail that as well! Suggestions and `philosophical' bug reports may be mailed to bug-bash AT gnu.org or posted to the Usenet newsgroup gnu.bash.bug.

       All bug reports should include:

       • 📌 The version number of bash
       • 💻 The hardware and operating system
       • 🛠️ The compiler used to compile
       • 📝 A description of the bug behaviour
       • 🧪 A short script or `recipe' which exercises the bug

       The bashbug command inserts the first three items automatically into the template it provides for filing a bug report.

       Comments and bug reports concerning this manual page should be directed to chet.ramey AT case.edu.

       Wait, the original text says "ALL bug reports should include:" with uppercase ALL. I should preserve that. Let me use ALL:

       ALL bug reports should include:

       Or I could keep it as uppercase text. Let me preserve the original phrasing exactly. Actually, looking at the original input more carefully: " ALL bug reports should include:" It's in uppercase. I'll preserve that as uppercase text. The original uses for the heading which becomes

       , so this is just plain text. I'll keep "ALL" as is. Let me also think about whether I should add a section like "Tip" or emoji for "If you have a fix, you are encouraged to mail that as well!" - I could add ✨ or 💡. Let me add that. Final:

       🐛 Bug Reports

       If you find a bug in bash, you should report it. But first, you should make sure that it really is a bug, and that it appears in the latest version of bash. The latest version is always available from ftp://ftp.gnu.org/pub/gnu/bash/.

       Once you have determined that a bug actually exists, use the bashbug command to submit a bug report. If you have a fix, you are encouraged to mail that as well! ✨ Suggestions and `philosophical' bug reports may be mailed to bug-bash AT gnu.org or posted to the Usenet newsgroup gnu.bash.bug.

       ALL bug reports should include:

       • 📌 The version number of bash
       • 💻 The hardware and operating system
       • 🛠️ The compiler used to compile
       • 📝 A description of the bug behaviour
       • 🧪 A short script or `recipe' which exercises the bug

       The bashbug command inserts the first three items automatically into the template it provides for filing a bug report.

       Comments and bug reports concerning this manual page should be directed to chet.ramey AT case.edu.

       Let me double-check XSS prevention (rule 13, 14): - All `` are part of allowed HTML tags:

       ,

       , , , ,

       ,
       • , (not used), (not used),
         (not used) - The original includes `` which is in the allowed list - All other tags are allowed I think this is good. Let me also check that I'm not using emojis at the start of paragraphs (rule 11). I'm not - the emojis are either: - In the heading (allowed) - Inside
       • items (allowed) - After periods within paragraphs (allowed) Good. Let me check rule 9: "Only add emoji comments AFTER the closing — never inside code blocks". I'm not using

          blocks here, so this doesn't apply. The  tags I use are inline , not 
         .
         
         Let me also re-check rule 17: "Preserve , ,  tags from the original — they carry semantic meaning. But do NOT add new  links inside code blocks." I'm preserving the  tags from the original and the  tags. The original  is the heading which I convert to 
         .
         
         Actually, I could use  for "ALL" to keep the original emphasis style. The original used uppercase, but in HTML we typically use  for emphasis. Let me add  to "ALL":
         
         Hmm, but the original didn't use  for "ALL" - it just used uppercase text. The original only used  for the heading "BUG REPORTS". So I should preserve the uppercase text style. Let me keep it as is.
         
         Final check - I think the output is good. Let me write it out.
         
         🐛 Bug Reports
         
         If you find a bug in bash, you should report it. But first, you should make sure that it really is a bug, and that it appears in the latest version of bash. The latest version is always available from ftp://ftp.gnu.org/pub/gnu/bash/.
         
         Once you have determined that a bug actually exists, use the bashbug command to submit a bug report. If you have a fix, you are encouraged to mail that as well! ✨ Suggestions and `philosophical' bug reports may be mailed to bug-bash AT gnu.org or posted to the Usenet newsgroup gnu.bash.bug.
         
         ALL bug reports should include:
         
         📌 The version number of bash
         💻 The hardware and operating system
         🛠️ The compiler used to compile
         📝 A description of the bug behaviour
         🧪 A short script or `recipe' which exercises the bug
         
         
         The bashbug command inserts the first three items automatically into the template it provides for filing a bug report.
         
         Comments and bug reports concerning this manual page should be directed to chet.ramey AT case.edu.
         🐛 BUGS
         
         🐻 It's too big and too slow.
         📜 There are some subtle differences between bash and traditional versions of sh, mostly because of the POSIX specification.
         😵‍💫 Aliases are confusing in some uses.
         🛑 Shell builtin commands and functions are not stoppable/restartable.
         ⏯️ Compound commands and command sequences of the form a ; b ; c are not handled gracefully when process suspension is attempted. When a process is stopped, the shell immediately executes the next command in the sequence. It suffices to place the sequence of commands between parentheses to force it into a subshell, which may be stopped as a unit.
         📦 Array variables may not (yet) be exported.
         🔄 There may be only one active coprocess at a time.
         
         GNU Bash 5.1                    2020 October 29                        BASH(1)