Instructions embedded in Bash script?

Question

Is there a way to make a bash script require a set of parameters when it's loaded, and if not, it will automatically spit out an echo to the screen giving instructions?

Looking at this example of a script called copy

user@localhost : user # ./copy  
Copy by SamplePerson  
Usage:  
copy [path/to/file] [path/to/destination]  
user@localhost : user #

I want it to make sure that if no parameters are given, it will automatically just spit out some predefined text on the echo.

I know how to ensure that the user enters correct values, but I just want the initial "usage" information be displayed for them.

Answer 1

I often use a construct like this:

case "$1" in
    'start')
        startProfile
        ;;

    'stop')
        stopProfile
        ;;

    'restart')
        stopProfile
        startProfile
        ;;

    *)
        echo "Usage $0 start|stop|restart <profile|application>"
esac

You have a switch-case that handles the normal cases and if none of them fit, then the default case prints the usage instructions.

Answer 2

You may try something like this:

#!/usr/bin/bash

[ $# -eq 0 ] && cat <<XXX && exit 0;
Copy by SamplePerson
Usage:
copy [path/to/file] [path/to/destination]
XXX

echo Check args "$@"

Sample run:

# ./test.sh
Copy by SamplePerson
Usage:
copy [path/to/file] [path/to/destination]

# ./test.sh -x -y
Check args -x -y

You can process arguments on a very convenient way using the getopts bash built-in command. Or the external getopt(3) command (especially if You use long (e.g. --longopt) arguments).