{ "content": [ { "type": "text", "text": "# bc (man)\n\n## NAME\n\nbc - An arbitrary precision calculator language\n\n## DESCRIPTION\n\nbc is a language that supports arbitrary precision numbers with interactive execution of\nstatements. There are some similarities in the syntax to the C programming language. A\nstandard math library is available by command line option. If requested, the math library is\ndefined before processing any files. bc starts by processing code from all the files listed\non the command line in the order listed. After all files have been processed, bc reads from\nthe standard input. All code is executed as it is read. (If a file contains a command to\nhalt the processor, bc will never read from the standard input.)\n\n## TLDR\n\n> An arbitrary precision calculator language.\n\n- Start an interactive session:\n `bc`\n- Start an interactive session with the standard math library enabled:\n `bc {{-i|--interactive}} {{-l|--mathlib}}`\n- Calculate an expression:\n `echo '{{5 / 3}}' | bc`\n- Execute a script:\n `bc {{path/to/script.bc}}`\n- Calculate an expression with the specified scale:\n `echo 'scale = {{10}}; {{5 / 3}}' | bc`\n- Calculate a sine/cosine/arctangent/natural logarithm/exponential function using `mathlib`:\n `echo '{{s|c|a|l|e}}({{1}})' | bc {{-l|--mathlib}}`\n- Execute an inline factorial script:\n `echo \"define factorial(n) { if (n <= 1) return 1; return n*factorial(n-1); }; factorial({{10}})\" | bc`\n\n*Source: tldr-pages*\n\n## Sections\n\n- **NAME**\n- **SYNTAX**\n- **DESCRIPTION** (9 subsections)\n- **ENVIRONMENT VARIABLES**\n- **DIAGNOSTICS**\n- **BUGS**\n- **AUTHOR**\n- **ACKNOWLEDGEMENTS**\n\nUse structuredContent.sections for detailed options, examples, and full documentation.\n" } ], "structuredContent": { "command": "bc", "section": "", "mode": "man", "summary": "bc - An arbitrary precision calculator language", "synopsis": null, "tldr_summary": "An arbitrary precision calculator language.", "tldr_examples": [ { "description": "Start an interactive session", "command": "bc" }, { "description": "Start an interactive session with the standard math library enabled", "command": "bc {{-i|--interactive}} {{-l|--mathlib}}" }, { "description": "Calculate an expression", "command": "echo '{{5 / 3}}' | bc" }, { "description": "Execute a script", "command": "bc {{path/to/script.bc}}" }, { "description": "Calculate an expression with the specified scale", "command": "echo 'scale = {{10}}; {{5 / 3}}' | bc" }, { "description": "Calculate a sine/cosine/arctangent/natural logarithm/exponential function using `mathlib`", "command": "echo '{{s|c|a|l|e}}({{1}})' | bc {{-l|--mathlib}}" }, { "description": "Execute an inline factorial script", "command": "echo \"define factorial(n) { if (n <= 1) return 1; return n*factorial(n-1); }; factorial({{10}})\" | bc" } ], "tldr_source": "official", "flags": [ { "flag": "-h", "long": "--help", "arg": null, "description": "Print the usage and exit." }, { "flag": "-i", "long": "--interactive", "arg": null, "description": "Force interactive mode." }, { "flag": "-l", "long": "--mathlib", "arg": null, "description": "Define the standard math library." }, { "flag": "-w", "long": "--warn", "arg": null, "description": "Give warnings for extensions to POSIX bc." }, { "flag": "-s", "long": "--standard", "arg": null, "description": "Process exactly the POSIX bc language." }, { "flag": "-q", "long": "--quiet", "arg": null, "description": "Do not print the normal GNU bc welcome." }, { "flag": "-v", "long": "--version", "arg": null, "description": "Print the version number and copyright and quit. NUMBERS The most basic element in bc is the number. Numbers are arbitrary precision numbers. This precision is both in the integer part and the fractional part. All numbers are represented internally in decimal and all computation is done in decimal. (This version truncates re‐ sults from divide and multiply operations.) There are two attributes of numbers, the length and the scale. The length is the total number of decimal digits used by bc to represent a number and the scale is the total number of decimal digits after the decimal point. For ex‐ ample: .000001 has a length of 6 and scale of 6. 1935.000 has a length of 7 and a scale of 3. VARIABLES Numbers are stored in two types of variables, simple variables and arrays. Both simple vari‐ ables and array variables are named. Names begin with a letter followed by any number of letters, digits and underscores. All letters must be lower case. (Full alpha-numeric names are an extension. In POSIX bc all names are a single lower case letter.) The type of vari‐ able is clear by the context because all array variable names will be followed by brackets ([]). There are four special variables, scale, ibase, obase, and last. scale defines how some op‐ erations use digits after the decimal point. The default value of scale is 0. ibase and obase define the conversion base for input and output numbers. The default for both input and output is base 10. last (an extension) is a variable that has the value of the last printed number. These will be discussed in further detail where appropriate. All of these variables may have values assigned to them as well as used in expressions. COMMENTS Comments in bc start with the characters /* and end with the characters */. Comments may start anywhere and appear as a single space in the input. (This causes comments to delimit other input items. For example, a comment can not be found in the middle of a variable name.) Comments include any newlines (end of line) between the start and the end of the com‐ ment. To support the use of scripts for bc, a single line comment has been added as an extension. A single line comment starts at a # character and continues to the next end of the line. The end of line character is not part of the comment and is processed normally. EXPRESSIONS The numbers are manipulated by expressions and statements. Since the language was designed to be interactive, statements and expressions are executed as soon as possible. There is no \"main\" program. Instead, code is executed as it is encountered. (Functions, discussed in detail later, are defined when encountered.) A simple expression is just a constant. bc converts constants into internal decimal numbers using the current input base, specified by the variable ibase. (There is an exception in functions.) The legal values of ibase are 2 through 36. (Bases greater than 16 are an exten‐ sion.) Assigning a value outside this range to ibase will result in a value of 2 or 36. In‐ put numbers may contain the characters 0–9 and A–Z. (Note: They must be capitals. Lower case letters are variable names.) Single digit numbers always have the value of the digit regard‐ less of the value of ibase. (i.e. A = 10.) For multi-digit numbers, bc changes all input digits greater or equal to ibase to the value of ibase-1. This makes the number ZZZ always be the largest 3 digit number of the input base. Full expressions are similar to many other high level languages. Since there is only one kind of number, there are no rules for mixing types. Instead, there are rules on the scale of expressions. Every expression has a scale. This is derived from the scale of original numbers, the operation performed and in many cases, the value of the variable scale. Legal values of the variable scale are 0 to the maximum number representable by a C integer. In the following descriptions of legal expressions, \"expr\" refers to a complete expression and \"var\" refers to a simple or an array variable. A simple variable is just a name and an array variable is specified as name[expr] Unless specifically mentioned the scale of the result is the maximum scale of the expressions involved. - expr The result is the negation of the expression. ++ var The variable is incremented by one and the new value is the result of the expression. -- var The variable is decremented by one and the new value is the result of the expression. var ++ The result of the expression is the value of the variable and then the variable is incremented by one. var -- The result of the expression is the value of the variable and then the variable is decremented by one. expr + expr The result of the expression is the sum of the two expressions. expr - expr The result of the expression is the difference of the two expressions. expr * expr The result of the expression is the product of the two expressions. expr / expr The result of the expression is the quotient of the two expressions. The scale of the result is the value of the variable scale. expr % expr The result of the expression is the \"remainder\" and it is computed in the following way. To compute a%b, first a/b is computed to scale digits. That result is used to compute a-(a/b)*b to the scale of the maximum of scale+scale(b) and scale(a). If scale is set to zero and both expressions are integers this expression is the integer remainder function. expr ^ expr The result of the expression is the value of the first raised to the second. The sec‐ ond expression must be an integer. (If the second expression is not an integer, a warning is generated and the expression is truncated to get an integer value.) The scale of the result is scale if the exponent is negative. If the exponent is positive the scale of the result is the minimum of the scale of the first expression times the value of the exponent and the maximum of scale and the scale of the first expression. (e.g. scale(a^b) = min(scale(a)*b, max( scale, scale(a))).) It should be noted that expr^0 will always return the value of 1. ( expr ) This alters the standard precedence to force the evaluation of the expression. var = expr The variable is assigned the value of the expression. var = expr This is equivalent to \"var = var expr\" with the exception that the \"var\" part is evaluated only once. This can make a difference if \"var\" is an array. Relational expressions are a special kind of expression that always evaluate to 0 or 1, 0 if the relation is false and 1 if the relation is true. These may appear in any legal expres‐ sion. (POSIX bc requires that relational expressions are used only in if, while, and for statements and that only one relational test may be done in them.) The relational operators are expr1 < expr2 The result is 1 if expr1 is strictly less than expr2. expr1 <= expr2 The result is 1 if expr1 is less than or equal to expr2. expr1 > expr2 The result is 1 if expr1 is strictly greater than expr2. expr1 >= expr2 The result is 1 if expr1 is greater than or equal to expr2. expr1 == expr2 The result is 1 if expr1 is equal to expr2. expr1 != expr2 The result is 1 if expr1 is not equal to expr2. Boolean operations are also legal. (POSIX bc does NOT have boolean operations). The result of all boolean operations are 0 and 1 (for false and true) as in relational expressions. The boolean operators are: !expr The result is 1 if expr is 0. expr && expr The result is 1 if both expressions are non-zero. expr || expr The result is 1 if either expression is non-zero. The expression precedence is as follows: (lowest to highest) || operator, left associative && operator, left associative ! operator, nonassociative Relational operators, left associative Assignment operator, right associative + and - operators, left associative *, / and % operators, left associative ^ operator, right associative unary - operator, nonassociative ++ and -- operators, nonassociative This precedence was chosen so that POSIX compliant bc programs will run correctly. This will cause the use of the relational and logical operators to have some unusual behavior when used with assignment expressions. Consider the expression: a = 3 < 5 Most C programmers would assume this would assign the result of \"3 < 5\" (the value 1) to the variable \"a\". What this does in bc is assign the value 3 to the variable \"a\" and then com‐ pare 3 to 5. It is best to use parenthesis when using relational and logical operators with the assignment operators. There are a few more special expressions that are provided in bc. These have to do with user defined functions and standard functions. They all appear as \"name(parameters)\". See the section on functions for user defined functions. The standard functions are: length ( expression ) The value of the length function is the number of significant digits in the expres‐ sion. read ( ) The read function (an extension) will read a number from the standard input, regard‐ less of where the function occurs. Beware, this can cause problems with the mixing of data and program in the standard input. The best use for this function is in a previously written program that needs input from the user, but never allows program code to be input from the user. The value of the read function is the number read from the standard input using the current value of the variable ibase for the conver‐ sion base. scale ( expression ) The value of the scale function is the number of digits after the decimal point in the expression. sqrt ( expression ) The value of the sqrt function is the square root of the expression. If the expres‐ sion is negative, a run time error is generated. STATEMENTS Statements (as in most algebraic languages) provide the sequencing of expression evaluation. In bc statements are executed \"as soon as possible.\" Execution happens when a newline in en‐ countered and there is one or more complete statements. Due to this immediate execution, newlines are very important in bc. In fact, both a semicolon and a newline are used as statement separators. An improperly placed newline will cause a syntax error. Because new‐ lines are statement separators, it is possible to hide a newline by using the backslash char‐ acter. The sequence \"\\\", where is the newline appears to bc as whitespace instead of a newline. A statement list is a series of statements separated by semicolons and new‐ lines. The following is a list of bc statements and what they do: (Things enclosed in brack‐ ets ([]) are optional parts of the statement.) expression This statement does one of two things. If the expression starts with \" ...\", it is considered to be an assignment statement. If the expression is not an assignment statement, the expression is evaluated and printed to the output. After the number is printed, a newline is printed. For example, \"a=1\" is an assign‐ ment statement and \"(a=1)\" is an expression that has an embedded assignment. All num‐ bers that are printed are printed in the base specified by the variable obase. The legal values for obase are 2 through BCBASEMAX. (See the section LIMITS.) For bases 2 through 16, the usual method of writing numbers is used. For bases greater than 16, bc uses a multi-character digit method of printing the numbers where each higher base digit is printed as a base 10 number. The multi-character digits are sep‐ arated by spaces. Each digit contains the number of characters required to represent the base ten value of \"obase-1\". Since numbers are of arbitrary precision, some num‐ bers may not be printable on a single output line. These long numbers will be split across lines using the \"\\\" as the last character on a line. The maximum number of characters printed per line is 70. Due to the interactive nature of bc, printing a number causes the side effect of assigning the printed value to the special variable last. This allows the user to recover the last value printed without having to retype the expression that printed the number. Assigning to last is legal and will overwrite the last printed value with the assigned value. The newly assigned value will remain until the next number is printed or another value is assigned to last. (Some instal‐ lations may allow the use of a single period (.) which is not part of a number as a short hand notation for for last.) string The string is printed to the output. Strings start with a double quote character and contain all characters until the next double quote character. All characters are take literally, including any newline. No newline character is printed after the string. print list The print statement (an extension) provides another method of output. The \"list\" is a list of strings and expressions separated by commas. Each string or expression is printed in the order of the list. No terminating newline is printed. Expressions are evaluated and their value is printed and assigned to the variable last. Strings in the print statement are printed to the output and may contain special characters. Special characters start with the backslash character (\\). The special characters recognized by bc are \"a\" (alert or bell), \"b\" (backspace), \"f\" (form feed), \"n\" (new‐ line), \"r\" (carriage return), \"q\" (double quote), \"t\" (tab), and \"\\\" (backslash). Any other character following the backslash will be ignored. { statementlist } This is the compound statement. It allows multiple statements to be grouped together for execution. if ( expression ) statement1 [else statement2] The if statement evaluates the expression and executes statement1 or statement2 de‐ pending on the value of the expression. If the expression is non-zero, statement1 is executed. If statement2 is present and the value of the expression is 0, then state‐ ment2 is executed. (The else clause is an extension.) while ( expression ) statement The while statement will execute the statement while the expression is non-zero. It evaluates the expression before each execution of the statement. Termination of the loop is caused by a zero expression value or the execution of a break statement. for ( [expression1] ; [expression2] ; [expression3] ) statement The for statement controls repeated execution of the statement. Expression1 is evalu‐ ated before the loop. Expression2 is evaluated before each execution of the state‐ ment. If it is non-zero, the statement is evaluated. If it is zero, the loop is ter‐ minated. After each execution of the statement, expression3 is evaluated before the reevaluation of expression2. If expression1 or expression3 are missing, nothing is evaluated at the point they would be evaluated. If expression2 is missing, it is the same as substituting the value 1 for expression2. (The optional expressions are an extension. POSIX bc requires all three expressions.) The following is equivalent code for the for statement: expression1; while (expression2) { statement; expression3; } break This statement causes a forced exit of the most recent enclosing while statement or for statement." } ], "examples": [], "see_also": [], "section_outline": [ { "name": "NAME", "lines": 2, "subsections": [] }, { "name": "SYNTAX", "lines": 2, "subsections": [] }, { "name": "DESCRIPTION", "lines": 14, "subsections": [ { "name": "-h, --help", "lines": 2, "flag": "-h", "long": "--help" }, { "name": "-i, --interactive", "lines": 2, "flag": "-i", "long": "--interactive" }, { "name": "-l, --mathlib", "lines": 2, "flag": "-l", "long": "--mathlib" }, { "name": "-w, --warn", "lines": 2, "flag": "-w", "long": "--warn" }, { "name": "-s, --standard", "lines": 2, "flag": "-s", "long": "--standard" }, { "name": "-q, --quiet", "lines": 2, "flag": "-q", "long": "--quiet" }, { "name": "-v, --version", "lines": 290, "flag": "-v", "long": "--version" }, { "name": "continue", "lines": 23 }, { "name": "warranty", "lines": 309 } ] }, { "name": "ENVIRONMENT VARIABLES", "lines": 19, "subsections": [] }, { "name": "DIAGNOSTICS", "lines": 4, "subsections": [] }, { "name": "BUGS", "lines": 5, "subsections": [] }, { "name": "AUTHOR", "lines": 3, "subsections": [] }, { "name": "ACKNOWLEDGEMENTS", "lines": 5, "subsections": [] } ], "sections": { "NAME": { "content": "bc - An arbitrary precision calculator language\n", "subsections": [] }, "SYNTAX": { "content": "bc [ -hlwsqv ] [long-options] [ file ... ]\n", "subsections": [] }, "DESCRIPTION": { "content": "bc is a language that supports arbitrary precision numbers with interactive execution of\nstatements. There are some similarities in the syntax to the C programming language. A\nstandard math library is available by command line option. If requested, the math library is\ndefined before processing any files. bc starts by processing code from all the files listed\non the command line in the order listed. After all files have been processed, bc reads from\nthe standard input. All code is executed as it is read. (If a file contains a command to\nhalt the processor, bc will never read from the standard input.)\n\nThis version of bc contains several extensions beyond traditional bc implementations and the\nPOSIX draft standard. Command line options can cause these extensions to print a warning or\nto be rejected. This document describes the language accepted by this processor. Extensions\nwill be identified as such.\n\nOPTIONS", "subsections": [ { "name": "-h, --help", "content": "Print the usage and exit.\n", "flag": "-h", "long": "--help" }, { "name": "-i, --interactive", "content": "Force interactive mode.\n", "flag": "-i", "long": "--interactive" }, { "name": "-l, --mathlib", "content": "Define the standard math library.\n", "flag": "-l", "long": "--mathlib" }, { "name": "-w, --warn", "content": "Give warnings for extensions to POSIX bc.\n", "flag": "-w", "long": "--warn" }, { "name": "-s, --standard", "content": "Process exactly the POSIX bc language.\n", "flag": "-s", "long": "--standard" }, { "name": "-q, --quiet", "content": "Do not print the normal GNU bc welcome.\n", "flag": "-q", "long": "--quiet" }, { "name": "-v, --version", "content": "Print the version number and copyright and quit.\n\nNUMBERS\nThe most basic element in bc is the number. Numbers are arbitrary precision numbers. This\nprecision is both in the integer part and the fractional part. All numbers are represented\ninternally in decimal and all computation is done in decimal. (This version truncates re‐\nsults from divide and multiply operations.) There are two attributes of numbers, the length\nand the scale. The length is the total number of decimal digits used by bc to represent a\nnumber and the scale is the total number of decimal digits after the decimal point. For ex‐\nample:\n.000001 has a length of 6 and scale of 6.\n1935.000 has a length of 7 and a scale of 3.\n\nVARIABLES\nNumbers are stored in two types of variables, simple variables and arrays. Both simple vari‐\nables and array variables are named. Names begin with a letter followed by any number of\nletters, digits and underscores. All letters must be lower case. (Full alpha-numeric names\nare an extension. In POSIX bc all names are a single lower case letter.) The type of vari‐\nable is clear by the context because all array variable names will be followed by brackets\n([]).\n\nThere are four special variables, scale, ibase, obase, and last. scale defines how some op‐\nerations use digits after the decimal point. The default value of scale is 0. ibase and\nobase define the conversion base for input and output numbers. The default for both input\nand output is base 10. last (an extension) is a variable that has the value of the last\nprinted number. These will be discussed in further detail where appropriate. All of these\nvariables may have values assigned to them as well as used in expressions.\n\nCOMMENTS\nComments in bc start with the characters /* and end with the characters */. Comments may\nstart anywhere and appear as a single space in the input. (This causes comments to delimit\nother input items. For example, a comment can not be found in the middle of a variable\nname.) Comments include any newlines (end of line) between the start and the end of the com‐\nment.\n\nTo support the use of scripts for bc, a single line comment has been added as an extension.\nA single line comment starts at a # character and continues to the next end of the line. The\nend of line character is not part of the comment and is processed normally.\n\nEXPRESSIONS\nThe numbers are manipulated by expressions and statements. Since the language was designed\nto be interactive, statements and expressions are executed as soon as possible. There is no\n\"main\" program. Instead, code is executed as it is encountered. (Functions, discussed in\ndetail later, are defined when encountered.)\n\nA simple expression is just a constant. bc converts constants into internal decimal numbers\nusing the current input base, specified by the variable ibase. (There is an exception in\nfunctions.) The legal values of ibase are 2 through 36. (Bases greater than 16 are an exten‐\nsion.) Assigning a value outside this range to ibase will result in a value of 2 or 36. In‐\nput numbers may contain the characters 0–9 and A–Z. (Note: They must be capitals. Lower case\nletters are variable names.) Single digit numbers always have the value of the digit regard‐\nless of the value of ibase. (i.e. A = 10.) For multi-digit numbers, bc changes all input\ndigits greater or equal to ibase to the value of ibase-1. This makes the number ZZZ always\nbe the largest 3 digit number of the input base.\n\nFull expressions are similar to many other high level languages. Since there is only one\nkind of number, there are no rules for mixing types. Instead, there are rules on the scale\nof expressions. Every expression has a scale. This is derived from the scale of original\nnumbers, the operation performed and in many cases, the value of the variable scale. Legal\nvalues of the variable scale are 0 to the maximum number representable by a C integer.\n\nIn the following descriptions of legal expressions, \"expr\" refers to a complete expression\nand \"var\" refers to a simple or an array variable. A simple variable is just a\nname\nand an array variable is specified as\nname[expr]\nUnless specifically mentioned the scale of the result is the maximum scale of the expressions\ninvolved.\n\n- expr The result is the negation of the expression.\n\n++ var The variable is incremented by one and the new value is the result of the expression.\n\n-- var The variable is decremented by one and the new value is the result of the expression.\n\nvar ++\nThe result of the expression is the value of the variable and then the variable is\nincremented by one.\n\nvar -- The result of the expression is the value of the variable and then the variable is\ndecremented by one.\n\nexpr + expr\nThe result of the expression is the sum of the two expressions.\n\nexpr - expr\nThe result of the expression is the difference of the two expressions.\n\nexpr * expr\nThe result of the expression is the product of the two expressions.\n\nexpr / expr\nThe result of the expression is the quotient of the two expressions. The scale of the\nresult is the value of the variable scale.\n\nexpr % expr\nThe result of the expression is the \"remainder\" and it is computed in the following\nway. To compute a%b, first a/b is computed to scale digits. That result is used to\ncompute a-(a/b)*b to the scale of the maximum of scale+scale(b) and scale(a). If\nscale is set to zero and both expressions are integers this expression is the integer\nremainder function.\n\nexpr ^ expr\nThe result of the expression is the value of the first raised to the second. The sec‐\nond expression must be an integer. (If the second expression is not an integer, a\nwarning is generated and the expression is truncated to get an integer value.) The\nscale of the result is scale if the exponent is negative. If the exponent is positive\nthe scale of the result is the minimum of the scale of the first expression times the\nvalue of the exponent and the maximum of scale and the scale of the first expression.\n(e.g. scale(a^b) = min(scale(a)*b, max( scale, scale(a))).) It should be noted that\nexpr^0 will always return the value of 1.\n\n( expr )\nThis alters the standard precedence to force the evaluation of the expression.\n\nvar = expr\nThe variable is assigned the value of the expression.\n\nvar = expr\nThis is equivalent to \"var = var expr\" with the exception that the \"var\" part is\nevaluated only once. This can make a difference if \"var\" is an array.\n\nRelational expressions are a special kind of expression that always evaluate to 0 or 1, 0 if\nthe relation is false and 1 if the relation is true. These may appear in any legal expres‐\nsion. (POSIX bc requires that relational expressions are used only in if, while, and for\nstatements and that only one relational test may be done in them.) The relational operators\nare\n\nexpr1 < expr2\nThe result is 1 if expr1 is strictly less than expr2.\n\nexpr1 <= expr2\nThe result is 1 if expr1 is less than or equal to expr2.\n\nexpr1 > expr2\nThe result is 1 if expr1 is strictly greater than expr2.\n\nexpr1 >= expr2\nThe result is 1 if expr1 is greater than or equal to expr2.\n\nexpr1 == expr2\nThe result is 1 if expr1 is equal to expr2.\n\nexpr1 != expr2\nThe result is 1 if expr1 is not equal to expr2.\n\nBoolean operations are also legal. (POSIX bc does NOT have boolean operations). The result\nof all boolean operations are 0 and 1 (for false and true) as in relational expressions. The\nboolean operators are:\n\n!expr The result is 1 if expr is 0.\n\nexpr && expr\nThe result is 1 if both expressions are non-zero.\n\nexpr || expr\nThe result is 1 if either expression is non-zero.\n\nThe expression precedence is as follows: (lowest to highest)\n|| operator, left associative\n&& operator, left associative\n! operator, nonassociative\nRelational operators, left associative\nAssignment operator, right associative\n+ and - operators, left associative\n*, / and % operators, left associative\n^ operator, right associative\nunary - operator, nonassociative\n++ and -- operators, nonassociative\n\nThis precedence was chosen so that POSIX compliant bc programs will run correctly. This will\ncause the use of the relational and logical operators to have some unusual behavior when used\nwith assignment expressions. Consider the expression:\na = 3 < 5\n\nMost C programmers would assume this would assign the result of \"3 < 5\" (the value 1) to the\nvariable \"a\". What this does in bc is assign the value 3 to the variable \"a\" and then com‐\npare 3 to 5. It is best to use parenthesis when using relational and logical operators with\nthe assignment operators.\n\nThere are a few more special expressions that are provided in bc. These have to do with user\ndefined functions and standard functions. They all appear as \"name(parameters)\". See the\nsection on functions for user defined functions. The standard functions are:\n\nlength ( expression )\nThe value of the length function is the number of significant digits in the expres‐\nsion.\n\nread ( )\nThe read function (an extension) will read a number from the standard input, regard‐\nless of where the function occurs. Beware, this can cause problems with the mixing\nof data and program in the standard input. The best use for this function is in a\npreviously written program that needs input from the user, but never allows program\ncode to be input from the user. The value of the read function is the number read\nfrom the standard input using the current value of the variable ibase for the conver‐\nsion base.\n\nscale ( expression )\nThe value of the scale function is the number of digits after the decimal point in the\nexpression.\n\nsqrt ( expression )\nThe value of the sqrt function is the square root of the expression. If the expres‐\nsion is negative, a run time error is generated.\n\nSTATEMENTS\nStatements (as in most algebraic languages) provide the sequencing of expression evaluation.\nIn bc statements are executed \"as soon as possible.\" Execution happens when a newline in en‐\ncountered and there is one or more complete statements. Due to this immediate execution,\nnewlines are very important in bc. In fact, both a semicolon and a newline are used as\nstatement separators. An improperly placed newline will cause a syntax error. Because new‐\nlines are statement separators, it is possible to hide a newline by using the backslash char‐\nacter. The sequence \"\\\", where is the newline appears to bc as whitespace instead\nof a newline. A statement list is a series of statements separated by semicolons and new‐\nlines. The following is a list of bc statements and what they do: (Things enclosed in brack‐\nets ([]) are optional parts of the statement.)\n\nexpression\nThis statement does one of two things. If the expression starts with \" ...\", it is considered to be an assignment statement. If the expression is\nnot an assignment statement, the expression is evaluated and printed to the output.\nAfter the number is printed, a newline is printed. For example, \"a=1\" is an assign‐\nment statement and \"(a=1)\" is an expression that has an embedded assignment. All num‐\nbers that are printed are printed in the base specified by the variable obase. The\nlegal values for obase are 2 through BCBASEMAX. (See the section LIMITS.) For\nbases 2 through 16, the usual method of writing numbers is used. For bases greater\nthan 16, bc uses a multi-character digit method of printing the numbers where each\nhigher base digit is printed as a base 10 number. The multi-character digits are sep‐\narated by spaces. Each digit contains the number of characters required to represent\nthe base ten value of \"obase-1\". Since numbers are of arbitrary precision, some num‐\nbers may not be printable on a single output line. These long numbers will be split\nacross lines using the \"\\\" as the last character on a line. The maximum number of\ncharacters printed per line is 70. Due to the interactive nature of bc, printing a\nnumber causes the side effect of assigning the printed value to the special variable\nlast. This allows the user to recover the last value printed without having to retype\nthe expression that printed the number. Assigning to last is legal and will overwrite\nthe last printed value with the assigned value. The newly assigned value will remain\nuntil the next number is printed or another value is assigned to last. (Some instal‐\nlations may allow the use of a single period (.) which is not part of a number as a\nshort hand notation for for last.)\n\nstring The string is printed to the output. Strings start with a double quote character and\ncontain all characters until the next double quote character. All characters are take\nliterally, including any newline. No newline character is printed after the string.\n\nprint list\nThe print statement (an extension) provides another method of output. The \"list\" is a\nlist of strings and expressions separated by commas. Each string or expression is\nprinted in the order of the list. No terminating newline is printed. Expressions are\nevaluated and their value is printed and assigned to the variable last. Strings in\nthe print statement are printed to the output and may contain special characters.\nSpecial characters start with the backslash character (\\). The special characters\nrecognized by bc are \"a\" (alert or bell), \"b\" (backspace), \"f\" (form feed), \"n\" (new‐\nline), \"r\" (carriage return), \"q\" (double quote), \"t\" (tab), and \"\\\" (backslash). Any\nother character following the backslash will be ignored.\n\n{ statementlist }\nThis is the compound statement. It allows multiple statements to be grouped together\nfor execution.\n\nif ( expression ) statement1 [else statement2]\nThe if statement evaluates the expression and executes statement1 or statement2 de‐\npending on the value of the expression. If the expression is non-zero, statement1 is\nexecuted. If statement2 is present and the value of the expression is 0, then state‐\nment2 is executed. (The else clause is an extension.)\n\nwhile ( expression ) statement\nThe while statement will execute the statement while the expression is non-zero. It\nevaluates the expression before each execution of the statement. Termination of the\nloop is caused by a zero expression value or the execution of a break statement.\n\nfor ( [expression1] ; [expression2] ; [expression3] ) statement\nThe for statement controls repeated execution of the statement. Expression1 is evalu‐\nated before the loop. Expression2 is evaluated before each execution of the state‐\nment. If it is non-zero, the statement is evaluated. If it is zero, the loop is ter‐\nminated. After each execution of the statement, expression3 is evaluated before the\nreevaluation of expression2. If expression1 or expression3 are missing, nothing is\nevaluated at the point they would be evaluated. If expression2 is missing, it is the\nsame as substituting the value 1 for expression2. (The optional expressions are an\nextension. POSIX bc requires all three expressions.) The following is equivalent\ncode for the for statement:\nexpression1;\nwhile (expression2) {\nstatement;\nexpression3;\n}\n\nbreak This statement causes a forced exit of the most recent enclosing while statement or\nfor statement.\n", "flag": "-v", "long": "--version" }, { "name": "continue", "content": "The continue statement (an extension) causes the most recent enclosing for statement\nto start the next iteration.\n\nhalt The halt statement (an extension) is an executed statement that causes the bc proces‐\nsor to quit only when it is executed. For example, \"if (0 == 1) halt\" will not cause\nbc to terminate because the halt is not executed.\n\nreturn Return the value 0 from a function. (See the section on functions.)\n\nreturn ( expression )\nReturn the value of the expression from a function. (See the section on functions.)\nAs an extension, the parenthesis are not required.\n\nPSEUDO STATEMENTS\nThese statements are not statements in the traditional sense. They are not executed state‐\nments. Their function is performed at \"compile\" time.\n\nlimits Print the local limits enforced by the local version of bc. This is an extension.\n\nquit When the quit statement is read, the bc processor is terminated, regardless of where\nthe quit statement is found. For example, \"if (0 == 1) quit\" will cause bc to termi‐\nnate.\n" }, { "name": "warranty", "content": "Print a longer warranty notice. This is an extension.\n\nFUNCTIONS\nFunctions provide a method of defining a computation that can be executed later. Functions\nin bc always compute a value and return it to the caller. Function definitions are \"dynamic\"\nin the sense that a function is undefined until a definition is encountered in the input.\nThat definition is then used until another definition function for the same name is encoun‐\ntered. The new definition then replaces the older definition. A function is defined as fol‐\nlows:\ndefine name ( parameters ) { newline\nautolist statementlist }\nA function call is just an expression of the form \"name(parameters)\".\n\nParameters are numbers or arrays (an extension). In the function definition, zero or more\nparameters are defined by listing their names separated by commas. All parameters are call\nby value parameters. Arrays are specified in the parameter definition by the notation\n\"name[]\". In the function call, actual parameters are full expressions for number parame‐\nters. The same notation is used for passing arrays as for defining array parameters. The\nnamed array is passed by value to the function. Since function definitions are dynamic, pa‐\nrameter numbers and types are checked when a function is called. Any mismatch in number or\ntypes of parameters will cause a runtime error. A runtime error will also occur for the call\nto an undefined function.\n\nThe autolist is an optional list of variables that are for \"local\" use. The syntax of the\nauto list (if present) is \"auto name, ... ;\". (The semicolon is optional.) Each name is the\nname of an auto variable. Arrays may be specified by using the same notation as used in pa‐\nrameters. These variables have their values pushed onto a stack at the start of the func‐\ntion. The variables are then initialized to zero and used throughout the execution of the\nfunction. At function exit, these variables are popped so that the original value (at the\ntime of the function call) of these variables are restored. The parameters are really auto\nvariables that are initialized to a value provided in the function call. Auto variables are\ndifferent than traditional local variables because if function A calls function B, B may ac‐\ncess function A's auto variables by just using the same name, unless function B has called\nthem auto variables. Due to the fact that auto variables and parameters are pushed onto a\nstack, bc supports recursive functions.\n\nThe function body is a list of bc statements. Again, statements are separated by semicolons\nor newlines. Return statements cause the termination of a function and the return of a\nvalue. There are two versions of the return statement. The first form, \"return\", returns\nthe value 0 to the calling expression. The second form, \"return ( expression )\", computes\nthe value of the expression and returns that value to the calling expression. There is an\nimplied \"return (0)\" at the end of every function. This allows a function to terminate and\nreturn 0 without an explicit return statement.\n\nFunctions also change the usage of the variable ibase. All constants in the function body\nwill be converted using the value of ibase at the time of the function call. Changes of\nibase will be ignored during the execution of the function except for the standard function\nread, which will always use the current value of ibase for conversion of numbers.\n\nSeveral extensions have been added to functions. First, the format of the definition has\nbeen slightly relaxed. The standard requires the opening brace be on the same line as the\ndefine keyword and all other parts must be on following lines. This version of bc will allow\nany number of newlines before and after the opening brace of the function. For example, the\nfollowing definitions are legal.\ndefine d (n) { return (2*n); }\ndefine d (n)\n{ return (2*n); }\n\nFunctions may be defined as void. A void function returns no value and thus may not be used\nin any place that needs a value. A void function does not produce any output when called by\nitself on an input line. The key word void is placed between the key word define and the\nfunction name. For example, consider the following session.\ndefine py (y) { print \"--->\", y, \"<---\", \"\\n\"; }\ndefine void px (x) { print \"--->\", x, \"<---\", \"\\n\"; }\npy(1)\n--->1<---\n0\npx(1)\n--->1<---\nSince py is not a void function, the call of py(1) prints the desired output and then prints\na second line that is the value of the function. Since the value of a function that is not\ngiven an explicit return statement is zero, the zero is printed. For px(1), no zero is\nprinted because the function is a void function.\n\nAlso, call by variable for arrays was added. To declare a call by variable array, the decla‐\nration of the array parameter in the function definition looks like \"*name[]\". The call to\nthe function remains the same as call by value arrays.\n\nMATH LIBRARY\nIf bc is invoked with the -l option, a math library is preloaded and the default scale is set\nto 20. The math functions will calculate their results to the scale set at the time of\ntheir call. The math library defines the following functions:\n\ns (x) The sine of x, x is in radians.\n\nc (x) The cosine of x, x is in radians.\n\na (x) The arctangent of x, arctangent returns radians.\n\nl (x) The natural logarithm of x.\n\ne (x) The exponential function of raising e to the value x.\n\nj (n,x)\nThe Bessel function of integer order n of x.\n\nEXAMPLES\nIn /bin/sh, the following will assign the value of \"pi\" to the shell variable pi.\npi=$(echo \"scale=10; 4*a(1)\" | bc -l)\n\nThe following is the definition of the exponential function used in the math library. This\nfunction is written in POSIX bc.\nscale = 20\n\n/* Uses the fact that e^x = (e^(x/2))^2\nWhen x is small enough, we use the series:\ne^x = 1 + x + x^2/2! + x^3/3! + ...\n*/\n\ndefine e(x) {\nauto a, d, e, f, i, m, v, z\n\n/* Check the sign of x. */\nif (x<0) {\nm = 1\nx = -x\n}\n\n/* Precondition x. */\nz = scale;\nscale = 4 + z + .44*x;\nwhile (x > 1) {\nf += 1;\nx /= 2;\n}\n\n/* Initialize the variables. */\nv = 1+x\na = x\nd = 1\n\nfor (i=2; 1; i++) {\ne = (a *= x) / (d *= i)\nif (e == 0) {\nif (f>0) while (f--) v = v*v;\nscale = z\nif (m) return (1/v);\nreturn (v/1);\n}\nv += e\n}\n}\n\nThe following is code that uses the extended features of bc to implement a simple program for\ncalculating checkbook balances. This program is best kept in a file so that it can be used\nmany times without having to retype it at every use.\nscale=2\nprint \"\\nCheck book program!\\n\"\nprint \" Remember, deposits are negative transactions.\\n\"\nprint \" Exit by a 0 transaction.\\n\\n\"\n\nprint \"Initial balance? \"; bal = read()\nbal /= 1\nprint \"\\n\"\nwhile (1) {\n\"current balance = \"; bal\n\"transaction? \"; trans = read()\nif (trans == 0) break;\nbal -= trans\nbal /= 1\n}\nquit\n\nThe following is the definition of the recursive factorial function.\ndefine f (x) {\nif (x <= 1) return (1);\nreturn (f(x-1) * x);\n}\n\nREADLINE AND LIBEDIT OPTIONS\nGNU bc can be compiled (via a configure option) to use the GNU readline input editor library\nor the BSD libedit library. This allows the user to do editing of lines before sending them\nto bc. It also allows for a history of previous lines typed. When this option is selected,\nbc has one more special variable. This special variable, history is the number of lines of\nhistory retained. For readline, a value of -1 means that an unlimited number of history\nlines are retained. Setting the value of history to a positive number restricts the number\nof history lines to the number given. The value of 0 disables the history feature. The de‐\nfault value is 100. For more information, read the user manuals for the GNU readline, his‐\ntory and BSD libedit libraries. One can not enable both readline and libedit at the same\ntime.\n\nDIFFERENCES\nThis version of bc was implemented from the POSIX P1003.2/D11 draft and contains several dif‐\nferences and extensions relative to the draft and traditional implementations. It is not im‐\nplemented in the traditional way using dc(1). This version is a single process which parses\nand runs a byte code translation of the program. There is an \"undocumented\" option (-c) that\ncauses the program to output the byte code to the standard output instead of running it. It\nwas mainly used for debugging the parser and preparing the math library.\n\nA major source of differences is extensions, where a feature is extended to add more func‐\ntionality and additions, where new features are added. The following is the list of differ‐\nences and extensions.\n\nLANG environment\nThis version does not conform to the POSIX standard in the processing of the LANG en‐\nvironment variable and all environment variables starting with LC.\n\nnames Traditional and POSIX bc have single letter names for functions, variables and arrays.\nThey have been extended to be multi-character names that start with a letter and may\ncontain letters, numbers and the underscore character.\n\nStrings\nStrings are not allowed to contain NUL characters. POSIX says all characters must be\nincluded in strings.\n\nlast POSIX bc does not have a last variable. Some implementations of bc use the period (.)\nin a similar way.\n\ncomparisons\nPOSIX bc allows comparisons only in the if statement, the while statement, and the\nsecond expression of the for statement. Also, only one relational operation is al‐\nlowed in each of those statements.\n\nif statement, else clause\nPOSIX bc does not have an else clause.\n\nfor statement\nPOSIX bc requires all expressions to be present in the for statement.\n\n&&, ||, !\nPOSIX bc does not have the logical operators.\n\nread function\nPOSIX bc does not have a read function.\n\nprint statement\nPOSIX bc does not have a print statement.\n\ncontinue statement\nPOSIX bc does not have a continue statement.\n\nreturn statement\nPOSIX bc requires parentheses around the return expression.\n\narray parameters\nPOSIX bc does not (currently) support array parameters in full. The POSIX grammar al‐\nlows for arrays in function definitions, but does not provide a method to specify an\narray as an actual parameter. (This is most likely an oversight in the grammar.)\nTraditional implementations of bc have only call by value array parameters.\n\nfunction format\nPOSIX bc requires the opening brace on the same line as the define key word and the\nauto statement on the next line.\n\n=+, =-, =*, =/, =%, =^\nPOSIX bc does not require these \"old style\" assignment operators to be defined. This\nversion may allow these \"old style\" assignments. Use the limits statement to see if\nthe installed version supports them. If it does support the \"old style\" assignment\noperators, the statement \"a =- 1\" will decrement a by 1 instead of setting a to the\nvalue -1.\n\nspaces in numbers\nOther implementations of bc allow spaces in numbers. For example, \"x=1 3\" would as‐\nsign the value 13 to the variable x. The same statement would cause a syntax error in\nthis version of bc.\n\nerrors and execution\nThis implementation varies from other implementations in terms of what code will be\nexecuted when syntax and other errors are found in the program. If a syntax error is\nfound in a function definition, error recovery tries to find the beginning of a state‐\nment and continue to parse the function. Once a syntax error is found in the func‐\ntion, the function will not be callable and becomes undefined. Syntax errors in the\ninteractive execution code will invalidate the current execution block. The execution\nblock is terminated by an end of line that appears after a complete sequence of state‐\nments. For example,\na = 1\nb = 2\nhas two execution blocks and\n{ a = 1\nb = 2 }\nhas one execution block. Any runtime error will terminate the execution of the current exe‐\ncution block. A runtime warning will not terminate the current execution block.\n\nInterrupts\nDuring an interactive session, the SIGINT signal (usually generated by the control-C\ncharacter from the terminal) will cause execution of the current execution block to be\ninterrupted. It will display a \"runtime\" error indicating which function was inter‐\nrupted. After all runtime structures have been cleaned up, a message will be printed\nto notify the user that bc is ready for more input. All previously defined functions\nremain defined and the value of all non-auto variables are the value at the point of\ninterruption. All auto variables and function parameters are removed during the clean\nup process. During a non-interactive session, the SIGINT signal will terminate the\nentire run of bc.\n\nLIMITS\nThe following are the limits currently in place for this bc processor. Some of them may have\nbeen changed by an installation. Use the limits statement to see the actual values.\n\nBCBASEMAX\nThe maximum output base is currently set at 999. The maximum input base is 16.\n\nBCDIMMAX\nThis is currently an arbitrary limit of 65535 as distributed. Your installation may\nbe different.\n\nBCSCALEMAX\nThe number of digits after the decimal point is limited to INTMAX digits. Also, the\nnumber of digits before the decimal point is limited to INTMAX digits.\n\nBCSTRINGMAX\nThe limit on the number of characters in a string is INTMAX characters.\n\nexponent\nThe value of the exponent in the raise operation (^) is limited to LONGMAX.\n\nvariable names\nThe current limit on the number of unique names is 32767 for each of simple variables,\narrays and functions.\n" } ] }, "ENVIRONMENT VARIABLES": { "content": "The following environment variables are processed by bc:\n\nPOSIXLYCORRECT\nThis is the same as the -s option.\n\nBCENVARGS\nThis is another mechanism to get arguments to bc. The format is the same as the com‐\nmand line arguments. These arguments are processed first, so any files listed in the\nenvironment arguments are processed before any command line argument files. This al‐\nlows the user to set up \"standard\" options and files to be processed at every invoca‐\ntion of bc. The files in the environment variables would typically contain function\ndefinitions for functions the user wants defined every time bc is run.\n\nBCLINELENGTH\nThis should be an integer specifying the number of characters in an output line for\nnumbers. This includes the backslash and newline characters for long numbers. As an\nextension, the value of zero disables the multi-line feature. Any other value of this\nvariable that is less than 3 sets the line length to 70.\n", "subsections": [] }, "DIAGNOSTICS": { "content": "If any file on the command line can not be opened, bc will report that the file is unavail‐\nable and terminate. Also, there are compile and run time diagnostics that should be self-ex‐\nplanatory.\n", "subsections": [] }, "BUGS": { "content": "Error recovery is not very good yet.\n\nEmail bug reports to bug-bc@gnu.org. Be sure to include the word ``bc'' somewhere in the\n``Subject:'' field.\n", "subsections": [] }, "AUTHOR": { "content": "Philip A. Nelson\nphilnelson@acm.org\n", "subsections": [] }, "ACKNOWLEDGEMENTS": { "content": "The author would like to thank Steve Sommars (Steve.Sommars@att.com) for his extensive help\nin testing the implementation. Many great suggestions were given. This is a much better\nproduct due to his involvement.\n\nGNU Project 2006-06-11 bc(1)", "subsections": [] } } } }