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



PROLOG
       This manual page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may dif-
       fer (consult the corresponding Linux manual page for details of Linux behavior), or the interface  may  not  be
       implemented on Linux.

NAME
       head - copy the first part of files

SYNOPSIS
       head [-n number][file...]

DESCRIPTION
       The head utility shall copy its input files to the standard output, ending the output for each file at a desig-
       nated point.

       Copying shall end at the point in each input file indicated by the -n number option. The option-argument number
       shall be counted in units of lines.

OPTIONS
       The  head  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:

       -n  number
              The first number lines of each input file shall be copied to  standard  output.  The  application  shall
              ensure that the number option-argument is a positive decimal integer.


       When  a file contains less than number lines, it shall be copied to standard output in its entirety. This shall
       not be an error.

       If no options are specified, head shall act as if -n 10 had been specified.

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.


STDIN
       The standard input shall be used only if no file operands are specified. See the INPUT FILES section.

INPUT FILES
       Input files shall be text files, but the line length is not restricted to {LINE_MAX} bytes.

ENVIRONMENT VARIABLES
       The following environment variables shall affect the execution of head:

       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 prece-
              dence 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 exam-
              ple, single-byte as opposed to multi-byte characters in arguments and input files).

       LC_MESSAGES
              Determine the locale that should be used to affect the format and contents of diagnostic messages  writ-
              ten 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 designated portions of the input files.

       If multiple file operands are specified, head shall precede the output for each with the header:


              "\n==> %s <==\n", <pathname>

       except that the first header written shall not include the initial <newline>.

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     Successful completion.

       >0     An error occurred.


CONSEQUENCES OF ERRORS
       Default.

       The following sections are informative.

APPLICATION USAGE
       The obsolescent - number form is withdrawn in this version.  Applications should use the -n number option.

EXAMPLES
       To write the first ten lines of all files (except those with a leading period) in the directory:


              head *

RATIONALE
       Although  it  is possible to simulate head with sed 10q for a single file, the standard developers decided that
       the popularity of head on historical BSD systems warranted its inclusion alongside tail.

       This standard version of head follows the Utility Syntax Guidelines.  The -n  option  was  added  to  this  new
       interface so that head and tail would be more logically related.

       There  is  no -c option (as there is in tail) because it is not historical practice and because other utilities
       in this volume of IEEE Std 1003.1-2001 provide similar functionality.

FUTURE DIRECTIONS
       None.

SEE ALSO
       sed, tail

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Stan-
       dard  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 .



IEEE/The Open Group                  2003                             HEAD(1P)