This runs the shell script as a separate shell. This runs the shell script from within the current shell script. The second form is useful for configuration files where environment variable are set for the script. Using configuration files in this manner makes it possible to write scripts that are automatically tailored for differ- ent situations. It does a lot for you.
String matching The test command provides limited string matching tests.
A more powerful trick is to match strings with the case switch. The Unix tradition is that programs should execute as qui- etly as possible. Especially for pipelines, cron jobs, etc. User prompts aren't required if there's no user. If there's a person out there, prod him a bit.