mirror of https://github.com/mkerrisk/man-pages
263 lines
8.6 KiB
Groff
263 lines
8.6 KiB
Groff
.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved
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.TH "LN" P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
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.\" ln
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.SH NAME
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ln \- link files
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.SH SYNOPSIS
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.LP
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\fBln\fP \fB[\fP\fB-fs\fP\fB]\fP \fIsource_file target_file\fP\fB
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.br
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.sp
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ln\fP \fB[\fP\fB-fs\fP\fB]\fP \fIsource_file\fP \fB...\fP \fItarget_dir\fP\fB
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.br
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\fP
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.SH DESCRIPTION
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.LP
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In the first synopsis form, the \fIln\fP utility shall create a new
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directory entry (link) at the destination path specified by
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the \fItarget_file\fP operand. If the \fB-s\fP option is specified,
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a symbolic link shall be created for the file specified by
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the \fIsource_file\fP operand. This first synopsis form shall be assumed
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when the final operand does not name an existing
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directory; if more than two operands are specified and the final is
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not an existing directory, an error shall result.
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.LP
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In the second synopsis form, the \fIln\fP utility shall create a new
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directory entry (link), or if the \fB-s\fP option is
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specified a symbolic link, for each file specified by a \fIsource_file\fP
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operand, at a destination path in the existing directory
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named by \fItarget_dir\fP.
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.LP
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If the last operand specifies an existing file of a type not specified
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by the System Interfaces volume of
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IEEE\ Std\ 1003.1-2001, the behavior is implementation-defined.
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.LP
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The corresponding destination path for each \fIsource_file\fP shall
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be the concatenation of the target directory pathname, a
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slash character, and the last pathname component of the \fIsource_file\fP.
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The second synopsis form shall be assumed when the
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final operand names an existing directory.
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.LP
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For each \fIsource_file\fP:
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.IP " 1." 4
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If the destination path exists:
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.RS
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.IP " a." 4
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If the \fB-f\fP option is not specified, \fIln\fP shall write a diagnostic
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message to standard error, do nothing more with the
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current \fIsource_file\fP, and go on to any remaining \fIsource_files\fP.
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.LP
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.IP " b." 4
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Actions shall be performed equivalent to the \fIunlink\fP() function
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defined in the
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System Interfaces volume of IEEE\ Std\ 1003.1-2001, called using \fIdestination\fP
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as the \fIpath\fP argument. If this
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fails for any reason, \fIln\fP shall write a diagnostic message to
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standard error, do nothing more with the current
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\fIsource_file\fP, and go on to any remaining \fIsource_files\fP.
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.LP
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.RE
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.LP
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.IP " 2." 4
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If the \fB-s\fP option is specified, \fIln\fP shall create a symbolic
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link named by the destination path and containing as its
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pathname \fIsource_file\fP. The \fIln\fP utility shall do nothing
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more with \fIsource_file\fP and shall go on to any remaining
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files.
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.LP
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.IP " 3." 4
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If \fIsource_file\fP is a symbolic link, actions shall be performed
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equivalent to the \fIlink\fP() function using the object that \fIsource_file\fP
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references as the \fIpath1\fP
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argument and the destination path as the \fIpath2\fP argument. The
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\fIln\fP utility shall do nothing more with \fIsource_file\fP
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and shall go on to any remaining files.
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.LP
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.IP " 4." 4
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Actions shall be performed equivalent to the \fIlink\fP() function
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defined in the System
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Interfaces volume of IEEE\ Std\ 1003.1-2001 using \fIsource_file\fP
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as the \fIpath1\fP argument, and the destination path
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as the \fIpath2\fP argument.
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.LP
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.SH OPTIONS
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.LP
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The \fIln\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-f\fP
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Force existing destination pathnames to be removed to allow the link.
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.TP 7
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\fB-s\fP
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Create symbolic links instead of hard links.
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.sp
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.SH OPERANDS
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.LP
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The following operands shall be supported:
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.TP 7
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\fIsource_file\fP
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A pathname of a file to be linked. If the \fB-s\fP option is specified,
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no restrictions on the type of file or on its
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existence shall be made. If the \fB-s\fP option is not specified,
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whether a directory can be linked is
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implementation-defined.
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.TP 7
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\fItarget_file\fP
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The pathname of the new directory entry to be created.
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.TP 7
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\fItarget_dir\fP
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A pathname of an existing directory in which the new directory entries
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are created.
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.sp
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.SH STDIN
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.LP
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Not used.
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.SH INPUT FILES
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.LP
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None.
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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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\fIln\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).
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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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Not used.
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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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All the specified files were linked successfully.
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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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None.
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.SH EXAMPLES
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.LP
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None.
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.SH RATIONALE
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.LP
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Some historic versions of \fIln\fP (including the one specified by
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the SVID) unlink the destination file, if it exists, by
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default. If the mode does not permit writing, these versions prompt
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for confirmation before attempting the unlink. In these
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versions the \fB-f\fP option causes \fIln\fP not to attempt to prompt
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for confirmation.
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.LP
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This allows \fIln\fP to succeed in creating links when the target
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file already exists, even if the file itself is not writable
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(although the directory must be). Early proposals specified this functionality.
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.LP
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This volume of IEEE\ Std\ 1003.1-2001 does not allow the \fIln\fP
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utility to unlink existing destination paths by
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default for the following reasons:
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.IP " *" 3
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The \fIln\fP utility has historically been used to provide locking
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for shell applications, a usage that is incompatible with
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\fIln\fP unlinking the destination path by default. There was no corresponding
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technical advantage to adding this
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functionality.
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.LP
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.IP " *" 3
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This functionality gave \fIln\fP the ability to destroy the link structure
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of files, which changes the historical behavior of
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\fIln\fP.
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.LP
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.IP " *" 3
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This functionality is easily replicated with a combination of \fIrm\fP
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and \fIln\fP.
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.LP
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.IP " *" 3
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It is not historical practice in many systems; BSD and BSD-derived
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systems do not support this behavior. Unfortunately,
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whichever behavior is selected can cause scripts written expecting
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the other behavior to fail.
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.LP
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.IP " *" 3
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It is preferable that \fIln\fP perform in the same manner as the \fIlink\fP()
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function,
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which does not permit the target to exist already.
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.LP
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.LP
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This volume of IEEE\ Std\ 1003.1-2001 retains the \fB-f\fP option
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to provide support for shell scripts depending on the
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SVID semantics. It seems likely that shell scripts would not be written
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to handle prompting by \fIln\fP and would therefore have
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specified the \fB-f\fP option.
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.LP
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The \fB-f\fP option is an undocumented feature of many historical
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versions of the \fIln\fP utility, allowing linking to
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directories. These versions require modification.
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.LP
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Early proposals of this volume of IEEE\ Std\ 1003.1-2001 also required
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a \fB-i\fP option, which behaved like the
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\fB-i\fP options in \fIcp\fP and \fImv\fP, prompting for
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confirmation before unlinking existing files. This was not historical
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practice for the \fIln\fP utility and has been omitted.
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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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\fIchmod\fP() , \fIfind\fP , \fIpax\fP , \fIrm\fP , the System Interfaces
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volume of IEEE\ Std\ 1003.1-2001, \fIlink\fP(), \fIunlink\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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