PROLOG | NAME | SYNOPSIS | DESCRIPTION | OPTIONS | OPERANDS | STDIN | INPUT FILES | ENVIRONMENT VARIABLES | ASYNCHRONOUS EVENTS | STDOUT | STDERR | OUTPUT FILES | EXTENDED DESCRIPTION | EXIT STATUS | CONSEQUENCES OF ERRORS | APPLICATION USAGE | EXAMPLES | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT

CAT(1P)                   POSIX Programmer's Manual                  CAT(1P)

PROLOG         top

       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         top

       cat — concatenate and print files

SYNOPSIS         top

       cat [−u] [file...]

DESCRIPTION         top

       The cat utility shall read files in sequence and shall write their
       contents to the standard output in the same sequence.

OPTIONS         top

       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
                 without delay as each is read.

OPERANDS         top

       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         top

       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         top

       The input files can be any file type.

ENVIRONMENT VARIABLES         top

       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 POSIX.1‐2008, 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         top

       Default.

STDOUT         top

       The standard output shall contain the sequence of bytes read from the
       input files. Nothing else shall be written to the standard output.

STDERR         top

       The standard error shall be used only for diagnostic messages.

OUTPUT FILES         top

       None.

EXTENDED DESCRIPTION         top

       None.

EXIT STATUS         top

       The following exit values shall be returned:

        0    All input files were output successfully.

       >0    An error occurred.

CONSEQUENCES OF ERRORS         top

       Default.

       The following sections are informative.

APPLICATION USAGE         top

       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 POSIX.1‐2008.

EXAMPLES         top

       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         top

       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         top

       None.

SEE ALSO         top

       more(1p)

       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(3p)

COPYRIGHT         top

       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 Electrical 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.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group                 2013                             CAT(1P)

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