Intel XENIX 286 Programmers Guide (86) - Tenox.tc

csh: C Shell XENIX Programming
Another important mechanism used in C shell scripts is the colon (:) modifier. We can
use the modifier :r here to extract the root of a file name. For example, this gives the
variable i the value /mnt/foo.bar:
% set i = /mnt/foo.bar
If you give this command:
% echo $i $i:r
the result is
/mnt/foo.bar /mnt/foo
This example shows how the :r modifier strips off the trailing ".bar". Other modifiers
take off the last component of a path name leaving the head :h or all but the last
component of a path name leaving the tail :t. These modifiers are fully described in the
entry csh in Appendix B, "Programming Commands." You can also use the command
substitution mechanism to perform modifications on strings and then re-enter the C
shell environment. Since each usage of this mechanism involves the creation of a new
process, it is much more expensive to use than the colon (:) modification mechanism.
Note also that the current implementation of the C shell limits the number of colon
modifiers on a "$" substitution to 1. Thus
produces
% set i = /albic
% echo $i $i:h:t
!albic /a/b:t
and does not do what you might expect.
Finally, we note that the number sign (#) lexically introduces a C shell comment in C
shell scripts (but not from the terminal). All subsequent characters on the input line
after a number sign are discarded by the C shell. This character can be quoted using ' or
\ to place it in an argument word.
Using Other Control Structures
The C shell also has control structures while and switch similar to those of C. These
take the forms
and
8-16
while ( expression )
commands
end