Tutorials Hut

Tutorials Hut

  • Unix For Testers

       Introduction to Unix
       Unix System Architecture
       Unix File System Structure
       Absolute and Relative Path
       Basic Unix Commands
       cal command in Unix
       who command in Unix
       date command in Unix
       clear command in Unix
       more command in Unix
       whoami command in Unix
       uname command in Unix
       man command in Unix
       echo command in Unix
       Unix File System Commands
       ls command in Unix
       cat command in Unix
       cp command in Unix
       mv command in Unix
       pwd command in Unix
       cd command in Unix
       mkdir command in Unix
       rmdir command in Unix
       rm command in Unix
       touch command in Unix
       dirname command in Unix
       tar command in Unix
       Unix Links(ln)
       Hard Link
       Soft Link
       Regular Expressions
        Basic Regular Expressions
       Interval Regular Expressions
       Pipes and Filters
       Unix Text Processing Commands
       cmp command in Unix
       diff command in Unix
       comm command in Unix
       cut command in Unix
       Paste command in Unix
       head command in Unix
       tail command in Unix
       wc command in Unix
       sort command in Unix
       grep command in Unix
       Process Related Command
       top command in Unix
       ps command in Unix
       nice command in Unix
       Kill command in Unix
       nohup command in Unix
       time command in Unix
       File Tranfer Commands in Unix
       file transfer using scp command
       file transfer using rlogin command
       file transfer using telnet command
       ssh(Secure Shell) command in Unix
       ftp file transfer command
       sftp file transfer command
       chmod command in Unix
       File Permission and File Security in Unix



  • Unix Links ( Symbolic links)

    Unix links, also known as a symlink or symbolic links, is a special type of file that points to another file or directory.

    We will learn below topics in this article:

      • A link in UNIX is a pointer to a file.
      • Creating links is a kind of shortcut to access a file.

    There are two types of links :

      1. Hard Link
      2. Soft Link or Symbolic Links
    Unix Links
      • Both the original file and hard linked file have the same inode numbers, therefore they reference the same physical file location.
      • If the original file is deleted , the link is not deleted, hard links are more flexible
      • Are more efficient (in terms of access time) as compared to soft links.
      • This can not be used to link a file on another file system, or to link directories

    Syntax:

    $ ln  [original filename] [link name] 
      • The original file and the link have different inode numbers. Each soft linked file points to the original file
      • When the original file is deleted, the link remains as an invalid link and will not behave correctly. It is called as hanging link
      • Soft Link contains the path for original file, if original file is removed it impacts the link functionality
      • This can be used to link file on a different file system 
      • Can be used to link directories

    Syntax:

    $ ln  -s [original filename] [link name]
    

    How to Use the ln Command to create Unix Links

    ln command in Unix is used for creating links between files. By default, the ln command creates hard links.

    To create a symbolic link, use the -s (–symbolic) option.

    1. Create link to a file

    SYNTAX:
    ln -s [OPTIONS] FILE LINK

    If both the FILE and LINK are given, ln will create a link from the file specified as the first argument (FILE) to the file specified as the second argument (LINK).
    If only one file is given as an argument or the second argument is a dot (.), ln will create a link to that file in the current working directory . The name of the symlink will be the same as the name of the file it points to.
    on successful execution , no output is displayed but returns zero.

    2. Creating Symlink To a File
    To create a symbolic link to a given file use -s option:

    SYNTAX:
    ln -s FILE symbolic_link

    The symbolic_link parameter is optional. The ln command will create a new link in your current directory in case it is not mentioned.

    The -> symbol shows the file the symlink points to.

    3. Create Symlinks to a Directory
    Directory name is used as the first parameter and the symlink as the second parameter.

    SYNTAX:
    ln -s DIRECTORY LINK

    Example:s

    Unix: create link to directory using ln command in Unix

    4. Overwriting Symlinks
    If you try to create a symbolic link that already exists , the ln command will print an error message.
    To overwrite the destination path of the symlink, use the -f (–force) option.

    SYNTAX:
    ln -sf FILE LINK

    5. Removing Symlinks
    unlink or rm  command is used to remove the links from file or directory.

    SYNTAX:
    
    unlink LINKNAME
         or
    rm LINKNAME
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