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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 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  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
       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()

       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
       original Standard can be obtained online at http://www.opengroup.org/unix/online.html .