cat(P)                                                   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 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 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  occurrences
              of '-' as a file operand.


STDIN
       The  standard  input shall be used only if no file oper-
       ands 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 internationaliza-
              tion  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 internationalization  variables
              used  to  determine  the  values  of locale cate-
              gories.)

       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 mes-
              sages 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 ter-
       minal, since buffering may delay the output.  The  pres-
       ence  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 speci-
       fied. 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  invoca-
       tion 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  con-
       sumed by cat the first time '-' was used as a file oper-
       and and an end-of-file condition would be detected imme-
       diately 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 dif-
       ferent 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  function-
       ality can be obtained from the -n option of the pr util-
       ity.

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 Operat-
       ing System Interface (POSIX), The Open Group Base Speci-
       fications Issue 6, Copyright (C) 2001-2003 by the Insti-
       tute 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 .



POSIX                         2003                       cat(P)
