IEEE 1003.1-2003, Single Unix Specification v3

																																				head																								  				 				The Open Group Base Specifications Issue 6				IEEE Std 1003.1, 2003 Edition				Copyright © 2001-2003 The IEEE and The Open Group, All Rights reserved.																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, 				"../basedefs/xbd_chap12.html#tag_12_02">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								[XSI] 				Determine the location of message catalogs for the processing of LC_MESSAGES . 				"[Option End]" border="0">																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 popularity of head on historical BSD systems warranted its inclusion alongside 				"../utilities/tail.html">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												CHANGE HISTORY												First released in Issue 4.												Issue 6												The obsolescent -number form is withdrawn.								The normative text is reworded to avoid use of the term "must" for application requirements.								The DESCRIPTION is updated to clarify that when a file contains less than the number of lines requested, the entire file is				copied to standard output.												End of informative text.																				UNIX ® is a registered Trademark of The Open Group.				POSIX ® is a registered Trademark of The IEEE.				[ Main Index | XBD | 				"../utilities/contents.html">XCU | XSH | XRAT				]