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CAT(P) CAT(P)
NAME
cat - concatenate and print files
SYNOPSIS
cat [-u][file ...]
DESCRIPTION
The cat utility shall read files in sequence and shall write their contents to the
standard output in the same sequence.
OPTIONS
The cat utility shall conform to the Base Definitions volume of
IEEE Std 1003.1-2001, Section 12.2, Utility Syntax Guidelines.
The following option shall be supported:
-u Write bytes from the input file to the standard output without delay as each
is read.
OPERANDS
The following operand shall be supported:
file A pathname of an input file. If no file operands are specified, the standard
input shall be used. If a file is ββ-ββ , the cat utility shall read from the
standard input at that point in the sequence. The cat utility shall not
close and reopen standard input when it is referenced in this way, but shall
accept multiple occurrences of ββ-ββ as a file operand.
STDIN
The standard input shall be used only if no file operands are specified, or if a
file operand is ββ-ββ . See the INPUT FILES section.
INPUT FILES
The input files can be any file type.
ENVIRONMENT VARIABLES
The following environment variables shall affect the execution of cat:
LANG Provide a default value for the internationalization variables that are
unset or null. (See the Base Definitions volume of IEEE Std 1003.1-2001,
Section 8.2, Internationalization Variables for the precedence of interna-
tionalization variables used to determine the values of locale categories.)
LC_ALL If set to a non-empty string value, override the values of all the other
internationalization variables.
LC_CTYPE
Determine the locale for the interpretation of sequences of bytes of text
data as characters (for example, single-byte as opposed to multi-byte char-
acters in arguments).
LC_MESSAGES
Determine the locale that should be used to affect the format and contents
of diagnostic messages written to standard error.
NLSPATH
Determine the location of message catalogs for the processing of LC_MESSAGES
.
ASYNCHRONOUS EVENTS
Default.
STDOUT
The standard output shall contain the sequence of bytes read from the input files.
Nothing else shall be written to the standard output.
STDERR
The standard error shall be used only for diagnostic messages.
OUTPUT FILES
None.
EXTENDED DESCRIPTION
None.
EXIT STATUS
The following exit values shall be returned:
0 All input files were output successfully.
>0 An error occurred.
CONSEQUENCES OF ERRORS
Default.
The following sections are informative.
APPLICATION USAGE
The -u option has value in prototyping non-blocking reads from FIFOs. The intent is
to support the following sequence:
mkfifo foo
cat -u foo > /dev/tty13 &
cat -u > foo
It is unspecified whether standard output is or is not buffered in the default
case. This is sometimes of interest when standard output is associated with a ter-
minal, since buffering may delay the output. The presence of the -u option guaran-
tees that unbuffered I/O is available. It is implementation-defined whether the cat
utility buffers output if the -u option is not specified. Traditionally, the -u
option is implemented using the equivalent of the setvbuf() function defined in the
System Interfaces volume of IEEE Std 1003.1-2001.
EXAMPLES
The following command:
cat myfile
writes the contents of the file myfile to standard output.
The following command:
cat doc1 doc2 > doc.all
concatenates the files doc1 and doc2 and writes the result to doc.all.
Because of the shell language mechanism used to perform output redirection, a com-
mand such as this:
cat doc doc.end > doc
causes the original data in doc to be lost.
The command:
cat start - middle - end > file
when standard input is a terminal, gets two arbitrary pieces of input from the ter-
minal with a single invocation of cat. Note, however, that if standard input is a
regular file, this would be equivalent to the command:
cat start - middle /dev/null end > file
because the entire contents of the file would be consumed by cat the first time ββ-ββ
was used as a file operand and an end-of-file condition would be detected immedi-
ately when ββ-ββ was referenced the second time.
RATIONALE
Historical versions of the cat utility include the options -e, -t, and -v, which
permit the ends of lines, <tab>s, and invisible characters, respectively, to be
rendered visible in the output. The standard developers omitted these options
because they provide too fine a degree of control over what is made visible, and
similar output can be obtained using a command such as:
sed -n -e ββs/$/$/ββ -e l pathname
The -s option was omitted because it corresponds to different functions in BSD and
System V-based systems. The BSD -s option to squeeze blank lines can be accom-
plished by the shell script shown in the following example:
sed -n ββ
# Write non-empty lines.
/./ {
p
d
}
# Write a single empty line, then look for more empty lines.
/^$/ p
# Get next line, discard the held <newline> (empty line),
# and look for more empty lines.
:Empty
/^$/ {
N
s/.//
b Empty
}
# Write the non-empty line before going back to search
# for the first in a set of empty lines.
p
The System V -s option to silence error messages can be accomplished by redirecting
the standard error. Note that the BSD documentation for cat uses the term "blank
line" to mean the same as the POSIX "empty lineββ: a line consisting only of a
<newline>.
The BSD -n option was omitted because similar functionality can be obtained from
the -n option of the pr utility.
FUTURE DIRECTIONS
None.
SEE ALSO
more , the System Interfaces volume of IEEE Std 1003.1-2001, setvbuf()
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std
1003.1, 2003 Edition, Standard for Information Technology -- Portable Operating
System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C)
2001-2003 by the Institute of Electrical and Electronics Engineers, Inc and The
Open Group. In the event of any discrepancy between this version and the original
IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is
the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .
POSIX 2003 CAT(P)
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