Интерактивная система просмотра системных руководств (man-ов)
head (1)
head (1) ( Solaris man: Команды и прикладные программы пользовательского уровня )
head (1) ( FreeBSD man: Команды и прикладные программы пользовательского уровня )
head (1) ( Русские man: Команды и прикладные программы пользовательского уровня )
head (1) ( Linux man: Команды и прикладные программы пользовательского уровня )
>> head (1) ( POSIX man: Команды и прикладные программы пользовательского уровня )
NAME
head - copy the first part of files
SYNOPSIS
head[-nnumber][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
-nnumber 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 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
The obsolescent -number form is withdrawn in this version.
Applications should use the -nnumber
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 popularity 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.
SEE ALSO
sed , tail
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 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 .
