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Next: 9.7 String Editing in ksh and bash
 

9.6 String Editing (Colon) Operators

When the C shell and bash do history substitutions ( 11.7 ) they can also edit the substitution. The C shell - but not bash  - can also edit variable substitutions ( 6.8 ) . For instance, in the first example below, when !$ contains /a/b/c , adding the "head" operator :h will give just the head of the pathname, /a/b .

For a complete but very terse list of these operators, see the csh manual page. We hope the examples below will help you understand these useful operators.

  • :h gives the head of a pathname ( 14.2 ) , as follows:

    % 
    
    echo /a/b/c
    
    
    /a/b/c
    % 
    
    echo !$:h
    
    
    echo /a/b
    /a/b

    That took off the filename and left the header. This also could be used with C shell variables ( 47.5 ) as:

    % 
    
    set x = /a/b/c
    
    
    % 
    
    echo $x
    
    
    /a/b/c
    % 
    
    echo $x:h
    
    
    /a/b

  • :r returns the root of a filename:

    % 
    
    echo xyz.c abc.c
    
    
    xyz.c abc.c
    % 
    
    echo !$:r
    
    
    echo abc
    abc

    The :r removed the .c from the last argument, leaving the root name. This could also be used in C shell variable names:

    % 
    
    set x = abc.c
    
    
    % 
    
    echo $x:r
    
    
    abc

  • :g For more than one name, you can add the g operator to make the operation global. For example:

    
    
    (...)
     
    
    
    % 
    
    set x = (a.a b.b c.c)
    
    
    % 
    
    echo $x:gr
    
    
    a b c

    The :gr operator stripped off all dot ( . ) suffixes. By the way, this use of g does not work with the history commands.

    This is the C shell's answer to the basename ( 45.18 ) command.

  • :e returns the extension (the part of the name after a dot). Using csh variables:

    % 
    
    set x=(abc.c)
    
    
    % 
    
    echo $x:e
    
    
    c

    No luck using that within history, either.

  • :t gives the tail of a pathname - the actual filename without the path:

    % 
    
    echo /a/b/c
    
    
    /a/b/c
    % 
    
    echo !$:t
    
    
    c

    With csh variables:

    % 
    
    set x=(/a/b/c)
    
    
    % 
    
    echo $x:t
    
    
    c

    And with multiple pathnames, you can do it globally with:

    % 
    
    set x=(/a/b/c /d/e/f /g/h/i)
    
    
    % 
    
    echo $x:gt
    
    
    c f i

    While the corresponding heads would be:

    % 
    
    set x=(/a/b/c /d/e/f /g/h/i)
    
    
    % 
    
    echo $x:gh
    
    
    /a/b /d/e /g/h

  • :p prints the command, but does not execute it ( 11.10 ) :

    % 
    
    echo *
    
    
    fn1 fn2 fn3
    % 
    
    !:p
    
    
    echo fn1 fn2 fn3

  • :q prevents further filename expansion, or prints the command as is:

    % 
    
    echo *
    
    
    fn1 fn2 fn3
    % 
    
    !:q
    
    
    echo *
    *

    The first command echoed the files in the directory, and when the :q was applied, it echoed only the special character.

  • :x is like :q , but it breaks the line into words. That is, when using :q , it is all one word, while :x will break it up into multiple words. [ :q and :x are more often used with C shell arrays ( 47.5 ) . - JP  ]

- DR


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