Format
- head [–B] [-W option[,option]...] [–b|–c|–k|–l|–m|–n num]
[file …file …]
- head [–B] [-W option[,option]...] [–num]
[file …file …]
Description
By default, head displays
the first 10 lines of each file given on the command line. If you
do not specify file, head reads
standard input (stdin).
Options
- –B
- Disables the automatic conversion of tagged files. This option
is ignored if the filecodeset or pgmcodeset options
(-W option) are specified.
- –b num
- Displays the first num blocks (a block
is 512 bytes) of each file.
- –c num
- Displays the first num bytes of each
file.
- –k num
- Displays the first num kilobytes (1024
bytes) of each file.
- –l num
- Displays the first num lines of each
file.
- –m num
- Displays the first num megabytes of
each file.
- –n num
- Displays the first num lines of each
file.
- –num
- Displays the first num lines of each
file.
- -W option[,option]...
- Specifies z/OS-specific options. The option keywords are case-sensitive. Possible
options are:
- filecodeset=codeset
- Performs text conversion from one code set to another when reading
from the file. The coded character set of the file is codeset. codeset can
be a code set name known to the system or a numeric coded character
set identifier (CCSID). Note that the command iconv -l lists
existing CCSIDs along with their corresponding code set names. The filecodeset and pgmcodeset options
can be used on files with any file tag.
If pgmcodeset is
specified but filecodeset is omitted, then
the default file code set is ISO8859-1 even if the file is tagged
with a different code set. If neither filecodeset nor pgmcodeset is
specified, text conversion will not occur unless automatic conversion
is enabled or the _TEXT_CONV environment variable indicates text conversion.
For more information about text conversion, see Controlling text conversion for z/OS UNIX shell commands.
If filecodeset or pgmcodeset is
specified, then automatic conversion is disabled for this command
invocation and the -B option is ignored
if it is also specified. See z/OS UNIX System Services Planning for
more information about automatic conversion.
When specifying values for filecodeset,
use the values that Unicode Service supports. For more information
about supported code sets, see z/OS Unicode Services User's Guide and Reference.
- pgmcodeset=codeset
- Performs text conversion from one code set to another when reading
from the file. The coded character set of the program (command) is codeset. codeset can
be a code set name known to the system or a numeric coded character
set identifier (CCSID). Note that the command iconv -l lists
existing CCSIDs along with their corresponding code set names. The filecodeset and pgmcodeset options
can be used on files with any file tag.
If filecodeset is
specified but pgmcodeset is omitted, then
the default program code set is IBM-1047. If neither filecodeset nor pgmcodeset is
specified, text conversion will not occur unless automatic conversion
is enabled or the _TEXT_CONV environment variable indicates text conversion.
For more information about text conversion, see Controlling text conversion for z/OS UNIX shell commands.
If filecodeset or pgmcodeset is
specified, then automatic conversion is disabled for this command
invocation and the -B option is ignored
if it is also specified. See z/OS UNIX System Services Planning for
more information about automatic conversion.
Restriction: The
only supported values for pgmcodeset are
IBM-1047 and 1047.
Examples
- To display the first 10 lines of a text file to the standard output
(stdout):
head myTextFile
- To display the first 400 bytes of a text file to the standard
output (stdout):
head -c 400 myTextFile
- To display the first 50 lines of a text file containing UTF-8 characters to the standard output (stdout),
assuming that:
- The text file is untagged and you do not want to tag it or enable
automatic conversion, and
- You cannot alter the tag (for example, you are displaying an untagged
public text file or a read-only text file):
head -n 50 -W filecodeset=UTF-8,pgmcodeset=IBM-1047 myUtf8File
- To display the first 10 lines of two text files containing EBCDIC
characters to the standard output (stdout), assuming that automatic
conversion has been enabled but the text files are incorrectly tagged
as ASCII:
head -B myMisTaggedFile01 myMisTaggedFile02
Localization
head uses
the following localization environment variables:
- LANG
- LC_ALL
- LC_CTYPE
- LC_MESSAGES
- NLSPATH
See Localization for more
information.
Environment variables
head uses
the following environment variable:
- _TEXT_CONV
- Contains text conversion information for the command. The text
conversion information is not used when either the -B option
or the filecodeset or pgmcodeset option
(-W option) is specified. For more information
about text conversion, see Controlling text conversion for z/OS UNIX shell commands.
Messages
Possible error messages include:
- Badly formed line or character count num
- The value num, following a –b, –c, –k, –l, –m,
or –n option, was not a valid number.
Portability
POSIX.2, X/Open Portability Guide.
This
program originated with Berkeley Software Distribution (BSD) and is
a frequent add-on to UNIX systems.
The
POSIX standard included only the –n num and –num options,
though it considers the latter obsolete.
Related information
cat, sed, tail