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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 '-' , 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 '-' as a file operand.
STDIN
The standard input shall be used only if no file oper-
ands are specified, or if a file operand is '-' . 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 internationaliza-
tion 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 internationalization variables
used to determine the values of locale cate-
gories.)
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 characters in arguments).
LC_MESSAGES
Determine the locale that should be used to
affect the format and contents of diagnostic mes-
sages 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 pres-
ence of the -u option guarantees that unbuffered I/O is
available. It is implementation-defined whether the cat
utility buffers output if the -u option is not speci-
fied. 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 command 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 terminal with a single invoca-
tion 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 con-
sumed by cat the first time '-' was used as a file oper-
and and an end-of-file condition would be detected imme-
diately when '-' 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 's/$/$/' -e l pathname
The -s option was omitted because it corresponds to dif-
ferent functions in BSD and System V-based systems. The
BSD -s option to squeeze blank lines can be accomplished
by the shell script shown in the following example:
sed -n '
# 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 line'': a
line consisting only of a <newline>.
The BSD -n option was omitted because similar function-
ality can be obtained from the -n option of the pr util-
ity.
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 Operat-
ing System Interface (POSIX), The Open Group Base Speci-
fications Issue 6, Copyright (C) 2001-2003 by the Insti-
tute 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.open-
group.org/unix/online.html .
POSIX 2003 cat(P)
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