man/cat1p/head.1p.txt
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head(P) head(P)
NAME head - copy the first part of files SYNOPSIS head [-n number][file...] DESCRIPTION The head utility shall copy its input files to the stan- dard output, ending the output for each file at a desig- nated point. Copying shall end at the point in each input file indi- cated by the -n number option. The option-argument num- ber 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 oper- ands 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 internationaliza- tion 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 cate- gories.) 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 mes- sages 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 pre- cede 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 ver- sion. 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 popularity of head on historical BSD systems war- ranted its inclusion alongside tail. This standard version of head follows the Utility Syntax Guidelines. The -n option was added to this new inter- face 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 Operat- ing System Interface (POSIX), The Open Group Base Speci- fications Issue 6, Copyright (C) 2001-2003 by the Insti- tute 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.open- group.org/unix/online.html . POSIX 2003 head(P) |