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       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

       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.1‐2008, 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.

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.1‐2008,  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.

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
           catu foo > /dev/tty13 &
           catu > 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.

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 startmiddleend > 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 startmiddle /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:

           sedn l pathname

       The latter also has the  advantage  that  its  output  is  unambiguous,
       whereas the output of historical catetv 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:

           sedn '
           # 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.1‐2008,  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
       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 .