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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 |
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HEAD(1P) POSIX Programmer's Manual HEAD(1P)
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.
head — copy the first part of files
head [−n number] [file...]
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.
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.
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.
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 shall be text files, but the line length is not
restricted to {LINE_MAX} bytes.
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.
Default.
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>.
The standard error shall be used only for diagnostic messages.
None.
None.
The following exit values shall be returned:
0 Successful completion.
>0 An error occurred.
Default.
The following sections are informative.
None.
To write the first ten lines of all files (except those with a
leading period) in the directory:
head −− *
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.
None.
sed(1p), tail(1p)
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 .
IEEE/The Open Group 2013 HEAD(1P)
Pages that refer to this page: tail(1p)
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