String Editing (Colon) Operators

When the C shells, zsh, and bash do history substitutions (Section 30.8) they can also edit the substitution. The C shells and zsh — but not bash — can also edit variable substitutions ( Section 35.9). (bash has a different syntax, which zsh understands, too.) 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 (Section 31.2), 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 (Section 35.9) 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

• :g makes the operation global if you have more than one name. 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 (Section 36.13) 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

  The corresponding heads would be:

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

• :p prints the command but does not execute it (Section 30.11):

  % 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.

[Wait, Dan, what about & on the right-hand side to repeat the previous substitution? And there's more since Dan wrote this article (in 1983!). tcsh also has :u to convert the first lowercase letter to uppercase and :l to convert the first uppercase letter to lowercase. In zsh, :u converts all letters to uppercase and :l converts all letter to lowercase. zsh also has f and F to repeat a substitution until it fails — and even more. Check your shell's manual page. — JP]