mirror of https://github.com/mkerrisk/man-pages
177 lines
4.9 KiB
Groff
177 lines
4.9 KiB
Groff
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.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved
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.TH "HEAD" P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
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.\" head
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.SH NAME
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head \- copy the first part of files
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.SH SYNOPSIS
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.LP
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\fBhead\fP \fB[\fP\fB-n\fP \fInumber\fP\fB][\fP\fIfile\fP\fB...\fP\fB]\fP
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.SH DESCRIPTION
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.LP
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The \fIhead\fP utility shall copy its input files to the standard
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output, ending the output for each file at a designated
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point.
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.LP
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Copying shall end at the point in each input file indicated by the
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\fB-n\fP \fInumber\fP option. The option-argument
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\fInumber\fP shall be counted in units of lines.
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.SH OPTIONS
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.LP
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The \fIhead\fP utility shall conform to the Base Definitions volume
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of IEEE\ Std\ 1003.1-2001, Section 12.2, Utility Syntax Guidelines.
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.LP
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The following option shall be supported:
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.TP 7
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\fB-n\ \fP \fInumber\fP
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The first \fInumber\fP lines of each input file shall be copied to
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standard output. The application shall ensure that the
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\fInumber\fP option-argument is a positive decimal integer.
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.sp
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.LP
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When a file contains less than \fInumber\fP lines, it shall be copied
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to standard output in its entirety. This shall not be an
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error.
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.LP
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If no options are specified, \fIhead\fP shall act as if \fB-n 10\fP
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had been specified.
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.SH OPERANDS
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.LP
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The following operand shall be supported:
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.TP 7
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\fIfile\fP
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A pathname of an input file. If no \fIfile\fP operands are specified,
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the standard input shall be used.
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.sp
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.SH STDIN
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.LP
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The standard input shall be used only if no \fIfile\fP operands are
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specified. See the INPUT FILES section.
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.SH INPUT FILES
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.LP
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Input files shall be text files, but the line length is not restricted
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to {LINE_MAX} bytes.
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.SH ENVIRONMENT VARIABLES
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.LP
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The following environment variables shall affect the execution of
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\fIhead\fP:
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.TP 7
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\fILANG\fP
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Provide a default value for the internationalization variables that
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are unset or null. (See the Base Definitions volume of
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IEEE\ Std\ 1003.1-2001, Section 8.2, Internationalization Variables
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for
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the precedence of internationalization variables used to determine
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the values of locale categories.)
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.TP 7
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\fILC_ALL\fP
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If set to a non-empty string value, override the values of all the
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other internationalization variables.
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.TP 7
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\fILC_CTYPE\fP
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Determine the locale for the interpretation of sequences of bytes
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of text data as characters (for example, single-byte as
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opposed to multi-byte characters in arguments and input files).
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.TP 7
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\fILC_MESSAGES\fP
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Determine the locale that should be used to affect the format and
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contents of diagnostic messages written to standard
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error.
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.TP 7
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\fINLSPATH\fP
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Determine the location of message catalogs for the processing of \fILC_MESSAGES
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\&.\fP
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.sp
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.SH ASYNCHRONOUS EVENTS
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.LP
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Default.
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.SH STDOUT
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.LP
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The standard output shall contain designated portions of the input
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files.
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.LP
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If multiple \fIfile\fP operands are specified, \fIhead\fP shall precede
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the output for each with the header:
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.sp
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.RS
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.nf
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\fB"\\n==> %s <==\\n", <\fP\fIpathname\fP\fB>
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\fP
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.fi
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.RE
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.LP
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except that the first header written shall not include the initial
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<newline>.
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.SH STDERR
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.LP
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The standard error shall be used only for diagnostic messages.
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.SH OUTPUT FILES
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.LP
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None.
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.SH EXTENDED DESCRIPTION
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.LP
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None.
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.SH EXIT STATUS
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.LP
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The following exit values shall be returned:
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.TP 7
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\ 0
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Successful completion.
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.TP 7
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>0
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An error occurred.
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.sp
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.SH CONSEQUENCES OF ERRORS
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.LP
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Default.
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.LP
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\fIThe following sections are informative.\fP
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.SH APPLICATION USAGE
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.LP
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The obsolescent \fB-\fP \fInumber\fP form is withdrawn in this version.
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Applications should use the \fB-n\fP \fInumber\fP
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option.
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.SH EXAMPLES
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.LP
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To write the first ten lines of all files (except those with a leading
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period) in the directory:
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.sp
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.RS
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.nf
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\fBhead *
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\fP
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.fi
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.RE
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.SH RATIONALE
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.LP
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Although it is possible to simulate \fIhead\fP with \fIsed\fP 10q
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for a single file, the
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standard developers decided that the popularity of \fIhead\fP on historical
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BSD systems warranted its inclusion alongside \fItail\fP.
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.LP
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This standard version of \fIhead\fP follows the Utility Syntax Guidelines.
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The \fB-n\fP option was added to this new interface
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so that \fIhead\fP and \fItail\fP would be more logically related.
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.LP
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There is no \fB-c\fP option (as there is in \fItail\fP) because it
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is not historical
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practice and because other utilities in this volume of IEEE\ Std\ 1003.1-2001
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provide similar functionality.
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.SH FUTURE DIRECTIONS
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.LP
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None.
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.SH SEE ALSO
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.LP
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\fIsed\fP , \fItail\fP
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.SH COPYRIGHT
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Portions of this text are reprinted and reproduced in electronic form
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from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
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-- Portable Operating System Interface (POSIX), The Open Group Base
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Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
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Electrical and Electronics Engineers, Inc and The Open Group. In the
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event of any discrepancy between this version and the original IEEE and
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The Open Group Standard, the original IEEE and The Open Group Standard
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is the referee document. The original Standard can be obtained online at
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http://www.opengroup.org/unix/online.html .
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