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

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

       head — copy the first part of files

SYNOPSIS         top

       head [−n number] [file...]

DESCRIPTION         top

       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         top

       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         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.

STDIN         top

       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         top

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

ENVIRONMENT VARIABLES         top

       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         top

       Default.

STDOUT         top

       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         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    Successful completion.

       >0    An error occurred.

CONSEQUENCES OF ERRORS         top

       Default.

       The following sections are informative.

APPLICATION USAGE         top

       None.

EXAMPLES         top

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

           head −− *

RATIONALE         top

       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         top

       None.

SEE ALSO         top

       sed(1p), tail(1p)

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

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                            HEAD(1P)