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 (con-
       sult 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 IEEE Std 1003.1-2001, Section 12.2, Utility Syntax Guide-
       lines.

       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  IEEE Std 1003.1-2001, Section 8.2, Internationalization Variables for the precedence of international-
              ization 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 stan-
              dard 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  guar-
       antees  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,  Copy-
       right (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  http://www.open-
       group.org/unix/online.html .



IEEE/The Open Group                                           2003                                                       CAT(1P)