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LN(1P)                     POSIX Programmer's Manual                    LN(1P)



PROLOG
       This manual page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may dif-
       fer (consult the corresponding Linux manual page for details of Linux behavior), or the interface  may  not  be
       implemented on Linux.

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
       directory, 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 System 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 destination 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 argu-
           ment.


OPTIONS
       The ln utility shall conform to the Base Definitions volume of IEEE Std 1003.1-2001, Section 12.2, Utility Syn-
       tax 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, Internationalization Variables for  the  prece-
              dence 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  exam-
              ple, single-byte as opposed to multi-byte characters in arguments).

       LC_MESSAGES
              Determine  the locale that should be used to affect the format and contents of diagnostic messages writ-
              ten 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  destination  file,  if  it
       exists, by default. If the mode does not permit writing, these versions prompt for confirmation before attempt-
       ing 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 specified this functionality.

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

        * The ln utility has historically been used to provide locking for shell applications, a usage that is  incom-
          patible 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 support 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 prac-
       tice 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, Stan-
       dard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base  Specifica-
       tions  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 Stan-
       dard,  the  original  IEEE  and  The  Open Group Standard is the referee document. The original Standard can be
       obtained online at http://www.opengroup.org/unix/online.html .



IEEE/The Open Group                  2003                               LN(1P)