LN(1P) - phpMan

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 differ (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 oper-
       and. 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  direc-
       tory  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  direc-
       tory.
       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  diag-
               nostic message to standard error, do nothing more with the cur-
               rent 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 argument.
OPTIONS
       The ln  utility  shall  conform  to  the  Base  Definitions  volume  of
       IEEE Std 1003.1-2001, Section 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  speci-
              fied,  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  Vari-
              ables  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).
       LC_MESSAGES
              Determine  the  locale  that should be used to affect the format
              and contents of diagnostic 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 destination 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 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 incompatible with ln unlinking
          the destination path by default. There was no corresponding  techni-
          cal 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 histori-
       cal 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 original Standard can be obtained online
       at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group                  2003                               LN(1P)