ln [-fhinsv] originalFile [newlink]
ln [-fhinsv] originalFile ... link_dir
link originalFile newlink

Creates a new directory entry (newlink) with the same modes as the original file.
Used to create multiple appearances of a file.
newlink points to the originalFile.

-i	interactivey prompts standard error with:"replace newlink?" if newlink exists. A response from standard input begining with y unlinks ( deletes ) newlink then creates newlink. -i overrides any previous -f
-f	force creation if the newlink file already exists. -f overrides any previous -i .
-v	verbose, showing files as they are processed, as in ln -v prefix*
-h,n	If the newlink_file or link_dir is a symbolic link, do not follow it. This is most useful with -f , to replace a symlink which may point to a directory.
-s	Create a symbolic link. ( no message is generated if original file does not exist! and return code is zero!)

The types of links are: hard links and symbolic links.

• hard links, created by default, add file directory entries that contain a duplicate of the pointer to the originalFile that was added when the originalFile was created.
  Hard link entries and the one added when the originalFile was created are indistinguishable.
  ls -l hardlinkfiles* includes a link count of the number of directory entries which point to a file.

   
   > ./reptpgm >  origfile
   > ls -l origfile
  -rw-r--r--  1 dgerman  devgrp  0 Apr  1 13:50 origfile
  
   > ln origfile hardLink
   > ls -l orig* hard* 
  -rw-r--r--  2 dgerman  devgrp  0 Apr  1 13:50 origfile
  -rw-r--r--  2 dgerman  devgrp  0 Apr  1 13:50 hardlink
  
  

  Changing the mode (permissions), stored in the inode, effects all entries.
  Removing the originalFile directory entry or those created using ln does not delete the file until the last entry is removed. ( i.e. When the link count is reduced to 0)
  Hard links may referer to different directories but may not span file systems or volumes and may not refer to directories ( Mac OSX darwin i.e., apple's version of BSD permits hard links of directories)
  ln will report "Cross-device link"
  Specify -s to create a symbolic directory link.

• symbolic links add a file directory entry that contains contain the full path of the originalFile.
  The originalFile is used when an open is performed on the symbolic link.
  ls -l displays an l as the first character, unique date fields (these are part of the directory entry, not the file) and an "arrow" ( -> ) pointing to the originalFile. additional date information is available using stat
  

  > ls -l *
  lrwxr-xr-x  1 dgerman  devgrp  6 Apr  1 14:08 symlink -> target
  -rw-r--r--  1 dgerman  devgrp  0 Apr  1 14:06 target
  

  The link count for both entries is 1.
  The size of symlink is size 6 since t,a,r,g,e,t is 6 characters.
  Changing the mode of the symbolic link actually effects the newlink !

  There is no information in the target file that a symbolic link to it exists!
  Unfortunately, removing the target file with out removing the synbolic link, causes accesses to the symbolic link to report: No such file or directory!
  

  stat on a symbolic link will return the target file
  lstat must be done to obtain information about the newlink.
  readlink is used to read the contents of a symbolic link.
  

   
  > ln -s "/Volumes/BACKUPS/notTimeMachine" mirror3
  > ls -l mirror3
  lrwxr-xr-x  dgerman  501  33 Sep7 22:22 mirror3 -> /Volumes/BACKUPS/notTimeMachine
  > ls -ld mirror3
  lrwxr-xr-x  dgerman  501  33 Sep7 22:22 mirror3 -> /Volumes/BACKUPS/notTimeMachine
  > stat mirror3
  234881028731036 lrwxr-xr-x dgerman (501) 0 33 
    "Sep7 22:22:34 2008" "Sep7 22:22:34 2008" "Sep7 22:22:34 2008" "Sep7 22:22:34 2008" 4096 8 0 mirror3
  > readlink mirror3
  /Volumes/BACKUPS/notTimeMachine
  > cd mirror3
   mirror3 > 
  

  Symbolic links may span file systems and may refer to directories.

Given one or two arguments, ln creates a hard link to an existing originalFile.


> cd ~
> ln ../yourdirectory/notes    Creates a hard link in my home directory to your file notes.
> ls -log docu ../yourdirectory/notes
-rwxr-xr-x 2 20 Jan 5 11:43 notes
-rwxr-xr-x 2 20 Jan 5 11:43 notes

Given more than two arguments, ln makes links in link_dir to all the named source files. The links made will have the same name as the files being linked to.

link takes exactly two filenames and creates a hard link. No options may be supplied.

SEE lstat,readlink,stat,symlink,symlink(7)

BUG: ln -s nofile newlink does not display a message if nofile does not exist and return code is set to 0!
Perhaps alias ln='ln

BSD December 30, 1993 BSD