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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 con‐
       tents to the standard output in the same sequence.

       The  cat	 utility  shall	 conform  to  the  Base	 Definitions volume of
       IEEE Std 1003.1-2001, 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 multi‐
	      ple 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 variables
	      that are unset or null. (See  the	 Base  Definitions  volume  of
	      IEEE Std 1003.1-2001,  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.

	      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.

	      Determine the location of message catalogs for the processing of
	      LC_MESSAGES .


       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.


       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 imple‐
       mented using the equivalent of the setvbuf() function  defined  in  the
       System Interfaces volume of IEEE Std 1003.1-2001.

       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 redi‐
       rection, 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

	      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 options -e, -t, and
       -v, which permit the ends of lines, <tab>s, and	invisible  characters,
       respectively, to be rendered visible in the output. The standard devel‐
       opers 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 -e 's/$/$/' -e l pathname

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

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


       more, the System Interfaces volume of IEEE Std 1003.1-2001, setvbuf()

       Portions	 of  this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
       --  Portable  Operating	System	Interface (POSIX), The Open Group Base
       Specifications Issue 6, Copyright (C) 2001-2003	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 .

IEEE/The Open Group		     2003			       CAT(1P)

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