C Shell Scripting/Parameters
Passing parameters to a script
[edit | edit source]In scripts, the variables $0
, $1
, $2
, and so on are known as positional parameters. The variable $0
refers to the name of the command and $1
, $2
and greater will be the parameters passed into the script.
When a csh script is invoked, the special variable argv is set to the wordlist of arguments given on the command line. Thus, as alternatives to the special variables $1
, $2
and so on, csh scripts can use $argv[1]
, $argv[2]
, and so on to access command line arguments. The value of the variable $#argv
is the number of arguments given.
For example write a myparams script:
#!/bin/csh -f echo The $0 command is called with $#argv parameters echo parameter 1 is $1 echo parameter 2 is $2 echo parameter 3 is $3 echo parameter 4 is $4 echo 2nd and on parameters are \"$argv[2-]\"
echo All Parameters are \"$argv\" echo All Parameters are \"$argv[*]\" echo All Parameters are \"$*\"
then run the command:
./myparams alpha beta omega
This prints out the following:
The ./myparams command is called with 3 parameters parameter 1 is alpha parameter 2 is beta parameter 3 is omega parameter 4 is All Parameters are "alpha beta omega" 2nd and on parameters are "beta omega"
If the parameter is missing the value of the position parameter will be a blank string as is the case of the 4th parameter. Also, you can get the entire or part of the command-line using the variable $argv which is a wordlist.
If you want to include spaces in a single parameter you must quote the value. For example running this command:
./myparams "alpha beta" omega
would print out the following:
The ./myparams command is called with 2 parameters parameter 1 is alpha beta parameter 2 is omega parameter 3 is parameter 4 is All Parameters are "alpha beta omega" 2nd and on parameters are "omega"
The alpha and beta value are now combined as a single value.
Lessons
[edit | edit source]- Parameters passed to a script are accessible using numbered variables like
$1
,$2
,$3
and so on. - Parameters passed to a script are also accessible using wordlist variable called
$argv