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Linux 2.6 - man page for ln (linux section 1posix)

LN(P)				    POSIX Programmer's Manual				    LN(P)

NAME
       ln - link files

SYNOPSIS
       ln [-fs] source_file target_file

       ln [-fs] source_file ... target_dir

DESCRIPTION
       In  the	first  synopsis form, the ln utility shall create a new directory entry (link) at
       the destination path specified by the target_file operand. If the -s option is  specified,
       a  symbolic  link shall be created for the file specified by the source_file operand. This
       first synopsis form shall be assumed when the final operand  does  not  name  an  existing
       directory; if more than two operands are specified and the final is not an existing direc-
       tory, an error shall result.

       In the second synopsis form, the ln utility shall create a new directory entry (link),  or
       if  the	-s  option is specified a symbolic link, for each file specified by a source_file
       operand, at a destination path in the existing directory named by target_dir.

       If the last operand specifies an existing file of a  type  not  specified  by  the  System
       Interfaces volume of IEEE Std 1003.1-2001, the behavior is implementation-defined.

       The  corresponding destination path for each source_file shall be the concatenation of the
       target directory pathname, a slash character, and  the  last  pathname  component  of  the
       source_file.   The  second  synopsis form shall be assumed when the final operand names an
       existing directory.

       For each source_file:

	1. If the destination path exists:

	    a. If the -f option is not specified, ln shall write a diagnostic message to standard
	       error,  do  nothing  more with the current source_file, and go on to any remaining
	       source_files.

	    b. Actions shall be performed equivalent to the unlink() function defined in the Sys-
	       tem  Interfaces	volume	of  IEEE Std 1003.1-2001, called using destination as the
	       path argument. If this fails for any reason, ln shall write a  diagnostic  message
	       to  standard error, do nothing more with the current source_file, and go on to any
	       remaining source_files.

	2. If the -s option is specified, ln shall create a symbolic link named by  the  destina-
	   tion  path and containing as its pathname source_file. The ln utility shall do nothing
	   more with source_file and shall go on to any remaining files.

	3. If source_file is a symbolic link, actions shall be performed equivalent to the link()
	   function  using  the  object that source_file references as the path1 argument and the
	   destination path as the path2 argument. The ln utility  shall  do  nothing  more  with
	   source_file and shall go on to any remaining files.

	4. Actions  shall  be  performed  equivalent to the link() function defined in the System
	   Interfaces volume of IEEE Std 1003.1-2001 using source_file as the path1 argument, and
	   the destination path as the path2 argument.

OPTIONS
       The  ln utility shall conform to the Base Definitions volume of IEEE Std 1003.1-2001, Sec-
       tion 12.2, Utility Syntax Guidelines.

       The following option shall be supported:

       -f     Force existing destination pathnames to be removed to allow the link.

       -s     Create symbolic links instead of hard links.

OPERANDS
       The following operands shall be supported:

       source_file
	      A pathname of a file to be linked. If the -s option is specified,  no  restrictions
	      on  the  type  of  file  or on its existence shall be made. If the -s option is not
	      specified, whether a directory can be linked is implementation-defined.

       target_file
	      The pathname of the new directory entry to be created.

       target_dir
	      A pathname of an existing directory in which the new directory entries are created.

STDIN
       Not used.

INPUT FILES
       None.

ENVIRONMENT VARIABLES
       The following environment variables shall affect the execution of ln:

       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, Inter-
	      nationalization 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 interna-
	      tionalization 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 argu-
	      ments).

       LC_MESSAGES
	      Determine the locale that should be used to affect the format and contents of diag-
	      nostic messages written to standard error.

       NLSPATH
	      Determine the location of message catalogs for the processing of LC_MESSAGES .

ASYNCHRONOUS EVENTS
       Default.

STDOUT
       Not used.

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     All the specified files were linked successfully.

       >0     An error occurred.

CONSEQUENCES OF ERRORS
       Default.

       The following sections are informative.

APPLICATION USAGE
       None.

EXAMPLES
       None.

RATIONALE
       Some historic versions of ln (including the one specified by the SVID) unlink the destina-
       tion file, if it exists, by default. If the mode does not permit writing,  these  versions
       prompt  for  confirmation  before  attempting  the unlink. In these versions the -f option
       causes ln not to attempt to prompt for confirmation.

       This allows ln to succeed in creating links when the target file already exists,  even  if
       the  file  itself is not writable (although the directory must be). Early proposals speci-
       fied this functionality.

       This volume of IEEE Std 1003.1-2001 does not allow the ln utility to unlink existing  des-
       tination paths by default for the following reasons:

	* The  ln utility has historically been used to provide locking for shell applications, a
	  usage that is incompatible with ln unlinking the destination path by default. There was
	  no corresponding technical advantage to adding this functionality.

	* This	functionality  gave  ln the ability to destroy the link structure of files, which
	  changes the historical behavior of ln.

	* This functionality is easily replicated with a combination of rm and ln.

	* It is not historical practice in many systems; BSD and BSD-derived systems do not  sup-
	  port	this  behavior.  Unfortunately,  whichever behavior is selected can cause scripts
	  written expecting the other behavior to fail.

	* It is preferable that ln perform in the same manner as the link() function, which  does
	  not permit the target to exist already.

       This  volume  of  IEEE Std 1003.1-2001  retains the -f option to provide support for shell
       scripts depending on the SVID semantics. It seems likely that shell scripts would  not  be
       written to handle prompting by ln and would therefore have specified the -f option.

       The  -f	option	is an undocumented feature of many historical versions of the ln utility,
       allowing linking to directories. These versions require modification.

       Early proposals of this volume of IEEE Std 1003.1-2001 also required a  -i  option,  which
       behaved	like  the  -i  options	in cp and mv, prompting for confirmation before unlinking
       existing files. This was not historical practice for the ln utility and has been omitted.

FUTURE DIRECTIONS
       None.

SEE ALSO
       chmod() , find , pax , rm , the System Interfaces volume of IEEE Std 1003.1-2001,  link(),
       unlink()

COPYRIGHT
       Portions  of  this  text  are  reprinted  and  reproduced in electronic form from IEEE Std
       1003.1, 2003 Edition, Standard for Information Technology  --  Portable	Operating  System
       Interface  (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by
       the Institute 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 orig-
       inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group			       2003					    LN(P)


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