cat(1p) — Linux manual page


CAT(1P)                 POSIX Programmer's Manual                CAT(1P)

PROLOG         top

       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.

NAME         top

       cat — concatenate and print files

SYNOPSIS         top

       cat [-u] [file...]

DESCRIPTION         top

       The cat utility shall read files in sequence and shall write
       their contents to the standard output in the same sequence.

OPTIONS         top

       The cat utility shall conform to the Base Definitions volume of
       POSIX.1‐2017, 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         top

       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         top

       The standard input shall be used only if no file operands are
       specified, or if a file operand is '-'.  See the INPUT FILES

INPUT FILES         top

       The input files can be any file type.


       The following environment variables shall affect the execution of

       LANG      Provide a default value for the internationalization
                 variables that are unset or null. (See the Base
                 Definitions volume of POSIX.1‐2017, 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).

                 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.



STDOUT         top

       The standard output shall contain the sequence of bytes read from
       the input files. Nothing else shall be written to the standard
       output.  If the standard output is a regular file, and is the
       same file as any of the input file operands, the implementation
       may treat this as an error.

STDERR         top

       The standard error shall be used only for diagnostic messages.

OUTPUT FILES         top




EXIT STATUS         top

       The following exit values shall be returned:

        0    All input files were output successfully.

       >0    An error occurred.



       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.1‐2017.

EXAMPLES         top

       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

       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 before cat even begins
       execution. This is true whether the cat command fails with an
       error or silently succeeds (the specification allows both
       behaviors). In order to append the contents of doc.end without
       losing the original contents of doc, this command should be used

           cat doc.end >> doc

       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.

RATIONALE         top

       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

           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.
           /./   {
           # Write a single empty line, then look for more empty lines.
           /^$/  p
           # Get next line, discard the held <newline> (empty line),
           # and look for more empty lines.
           /^$/  {
                 b Empty
           # 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

       The BSD -n option was omitted because similar functionality can
       be obtained from the -n option of the pr utility.



SEE ALSO         top


       The Base Definitions volume of POSIX.1‐2017, Chapter 8,
       Environment Variables, Section 12.2, Utility Syntax Guidelines

       The System Interfaces volume of POSIX.1‐2017, setvbuf(3p)

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic
       form from IEEE Std 1003.1-2017, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The
       Open Group Base Specifications Issue 7, 2018 Edition, Copyright
       (C) 2018 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 .

       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 .

IEEE/The Open Group               2017                           CAT(1P)

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