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POSIX 1003.1 - man page for cat (posix section 1p)

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

PROLOG
       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 stan-
       dard 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 stan-
		 dard 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.

STDIN
       The standard input shall be used only if no file operands are specified, or if a file  op-
       erand 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,  Interna-
		 tionalization	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  inter-
		 nationalization 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
	   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 buffer-
       ing 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 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 ren-
       dered 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.1-2008, 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 discrep-
       ancy 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)
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