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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 con‐
       tents 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	 with‐
		 out delay as each is read.

OPERANDS
       The following operand shall be supported:

       file	 A  pathname  of an input file. If no file operands are speci‐
		 fied, 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	speci‐
       fied, 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 vari‐
		 ables that are unset or null. (See the Base Definitions  vol‐
		 ume  of POSIX.1‐2008, 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.

       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 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 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	 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
       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.1‐2008, 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 Electri‐
       cal 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.ker‐
       nel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group		     2013			       CAT(1P)
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