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



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

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.1-2017, 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 1100 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.1-2017, 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
       When using head to process pathnames, it is recommended that LC_ALL, or
       at least LC_CTYPE and LC_COLLATE, are set to POSIX or C in the
       environment, since pathnames can contain byte sequences that do not
       form valid characters in some locales, in which case the utility's
       behavior would be undefined. In the POSIX locale each byte is a valid
       single-byte character, and therefore this problem is avoided.

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.1-2017 provide similar functionality.

FUTURE DIRECTIONS
       None.

SEE ALSO
       sed, tail

       The Base Definitions volume of POSIX.1-2017, Chapter _8, Environment
       Variables, Section 12.2, Utility Syntax Guidelines

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1-2017, Standard for Information Technology --
       Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, 2018 Edition, Copyright (C) 2018 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 .

       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                  2017                              HEAD(1)
