👤
Home Man
Search
Today's Posts
Register

Linux & Unix Commands - Search Man Pages
Man Page or Keyword Search:
Select Section of Man Page:
Select Man Page Repository:

Linux 2.6 - man page for cat (linux section 1posix)

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

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 IEEE Std 1003.1-2001, Sec-
       tion 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 occur-
	      rences 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 IEEE Std 1003.1-2001, Section 8.2, Inter-
	      nationalization 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  interna-
	      tionalization 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  argu-
	      ments).

       LC_MESSAGES
	      Determine the locale that should be used to affect the format and contents of diag-
	      nostic 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 IEEE Std 1003.1-2001.

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

COPYRIGHT
       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 orig-
       inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group			       2003					   CAT(P)


All times are GMT -4. The time now is 09:53 PM.

Unix & Linux Forums Content Copyrightę1993-2018. All Rights Reserved.
×
UNIX.COM Login
Username:
Password:  
Show Password