phpMan

/* Void Main's man pages */

{ phpMan } else { main(); }

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 differ (con-
sult 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 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 precedence of international-
ization 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 stan-
dard 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 popu-
larity 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.