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PROLOG | NAME | SYNOPSIS | DESCRIPTION | OPTIONS | OPERANDS | STDIN | INPUT FILES | ENVIRONMENT VARIABLES | ASYNCHRONOUS EVENTS | STDOUT | STDERR | OUTPUT FILES | EXTENDED DESCRIPTION | EXIT STATUS | CONSEQUENCES OF ERRORS | APPLICATION USAGE | EXAMPLES | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
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CAT(1P) POSIX Programmer's Manual CAT(1P)
This manual page is part of the POSIX Programmer's Manual. The Linux
implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior), or
the interface may not be implemented on Linux.
cat — concatenate and print files
cat [−u] [file...]
The cat utility shall read files in sequence and shall write their
contents 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
without delay as each is read.
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.
The standard input shall be used only if no file operands are
specified, 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
variables that are unset or null. (See the Base Definitions
volume of POSIX.1‐2008, Section 8.2, Internationalization
Variables 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).
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.
Default.
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.
None.
None.
The following exit values shall be returned:
0 All input files were output successfully.
>0 An error occurred.
Default.
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:
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 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 implemented using the equivalent of the setvbuf()
function defined in the System Interfaces volume of POSIX.1‐2008.
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 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 '−' 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 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 functionality can be
obtained from the −n option of the pr utility.
None.
more(1p)
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(3p)
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 Electrical 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 .
Any typographical or formatting errors that appear in this page are
most likely to have been introduced during the conversion of the
source files to man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2013 CAT(1P)
Pages that refer to this page: tee(1p)
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