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

XENIX Programming csh: C Shell
Using the argv Variable
A csh command script can be interpreted by typing
csh script [argument] ...
where script is the name of the file containing a group of C shell commands and
argument is a sequence of command arguments. The C shell places these arguments in
the variable argv and then begins to read commands from script. These parameters are
then available through the same mechanisms used to reference any other C shell
variables.
If you make the file script executable by typing
or
chmod 755 script
chmod + x script
and then place a C shell com ment at the beginning of the C shell script (i.e., begin the
file with a number sign (#)), then /bin/csh will automatically be invoked to execute
script when you type
script
If the file does not begin with a nu mber sign (#), then the C shell will call the standard
shell /bin/sh to execute it. Thus from the C shell, you can execute scripts written for
either the C shell or the standard shell. In the standard shell sh, you can only execute
scripts written for sh and not scripts written for the C shell.
Substituting Shell Variables
After each input line is broken into words and history substitutions are done on it, the
input line is parsed into distinct commands. Before each command is executed, a
mechanism known as variable substitution is performed on these words. Keyed by the
dollar sign ($), this substitution replaces the names of variables by their values. Thus
echo $argv
when placed in a command script, would cause the current value of the variable argv to
be echoed to the output of the C shell script. It is an error for argv to be unset at this
point.
A number of notations are provided for accessing components and attributes of
variables. The notation
$?name
expands to 1 if name is set or to 0 if name is not set. It is the fundamental mechanism
used for checking whether particular variables have been assigned values. All other
forms of reference to undefined variables cause errors.
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