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



PROLOG
       This manual page is part of the POSIX Programmer's Manual.  The OS
       implementation of this interface may differ (consult the corresponding
       OS manual page for details of OS behavior), or the interface may not be
       implemented on OS.

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
       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
       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 operands 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 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).

       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.  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
       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 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
       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 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 instead:


           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
       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.

FUTURE DIRECTIONS
       None.

SEE ALSO
       more

       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()

COPYRIGHT
       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 http://www.opengroup.org/unix/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                  2017                               CAT(1)
