xenial (1) head.1posix.gz

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PROLOG
       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
       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
       designated 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 POSIX.1‐2008, 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 if no file operands are specified, and shall be used if a file operand
       is '−' and the implementation treats the '−' as meaning standard input.  Otherwise,  the  standard  input
       shall not be used.  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 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 and input files).

       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 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
       None.


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.

       POSIX.1‐2008 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. Earlier versions of this standard
       allowed a −number option. This form is no longer specified by POSIX.1‐2008 but may  be  present  in  some
       implementations.

       There  is  no  −c  option  (as  there is in tail) because it is not historical practice and because other
       utilities in this volume of POSIX.1‐2008 provide similar functionality.


FUTURE DIRECTIONS
       None.


SEE ALSO
       sed, tail

       The Base Definitions volume of POSIX.1‐2008, Chapter 8,  Environment  Variables,  Section  12.2,  Utility
       Syntax Guidelines


       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 .