CAT(1P) POSIX Programmer's Manual CAT(1P)PROLOG
This manual page is part of the POSIX Programmer's Manual. The Linux
implementation of this interface may differ (consult the corresponding
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NAMEcat — concatenate and print files
SYNOPSIScat [−u] [file...]
The cat utility shall read files in sequence and shall write their con‐
tents to the standard output in the same sequence.
The cat utility shall conform to the Base Definitions volume of
POSIX.1‐2008, Section 12.2, Utility Syntax Guidelines.
The following option shall be supported:
−u Write bytes from the input file to the standard output with‐
out delay as each is read.
The following operand shall be supported:
file A pathname of an input file. If no file operands are speci‐
fied, 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.
The standard input shall be used only if no file operands are speci‐
fied, or if a file operand is '−'. See the INPUT FILES section.
The input files can be any file type.
The following environment variables shall affect the execution of cat:
LANG Provide a default value for the internationalization vari‐
ables that are unset or null. (See the Base Definitions vol‐
ume of POSIX.1‐2008, Section 8.2, Internationalization Vari‐
ables for the precedence of internationalization 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 characters in arguments).
Determine the locale that should be used to affect the format
and contents of diagnostic messages written to standard
NLSPATH Determine the location of message catalogs for the processing
The standard output shall contain the sequence of bytes read from the
input files. Nothing else shall be written to the standard output.
The standard error shall be used only for diagnostic messages.
The following exit values shall be returned:
0 All input files were output successfully.
>0 An error occurred.
CONSEQUENCES OF ERRORS
The following sections are informative.
The −u option has value in prototyping non-blocking reads from FIFOs.
The intent is to support the following sequence:
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 terminal, since buffering may delay the output. The
presence 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 specified. Traditionally, the −u option is imple‐
mented using the equivalent of the setvbuf() function defined in the
System Interfaces volume of POSIX.1‐2008.
The following command:
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 redi‐
rection, a command such as this:
cat doc doc.end > doc
causes the original data in doc to be lost.
cat start − middle − end > file
when standard input is a terminal, gets two arbitrary pieces of input
from the terminal with a single invocation of cat. Note, however, that
if standard input is a regular file, this would be equivalent to the
cat start − middle /dev/null end > file
because the entire contents of the file would be consumed by cat the
first time '−' was used as a file operand and an end-of-file condition
would be detected immediately when '−' was referenced the second time.
Historical versions of the cat utility include the −e, −t, and −v,
options which permit the ends of lines, <tab> characters, 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 l pathname
The latter also has the advantage that its output is unambiguous,
whereas the output of historical cat −etv is not.
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 accomplished by the shell script shown in the following
sed −n '
# Write non-empty lines.
# Write a single empty line, then look for more empty lines.
# Get next line, discard the held <newline> (empty line),
# and look for more empty lines.
# Write the non-empty line before going back to search
# for the first in a set of empty lines.
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 functionality can be
obtained from the −n option of the pr utility.
The Base Definitions volume of POSIX.1‐2008, Chapter 8, Environment
Variables, Section 12.2, Utility Syntax Guidelines
The System Interfaces volume of POSIX.1‐2008, setvbuf()COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
cal and Electronics Engineers, Inc and The Open Group. (This is
POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) 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.unix.org/online.html .
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IEEE/The Open Group 2013 CAT(1P)