BASH - Throw usage warning if no command line parameter is passed as an argument

Question

I found an answer here for a question on counting number of parameters passed argument to a BASH script. I'm interested on the line : ${1?"Usage: $0 ARGUMENT"} where it throws warning if no parameter is given.

Now I would like to invoke a usage function Usage using : ${1?"Usage: $0 ARGUMENT"} but I do not know how to do it. I tried : ${1?Usage} and BASH throws an error on this line. Can some suggest how to invoke a function using this.

The sample script is as below,

#!/bin/bash

function Usage() {
    echo "Usage: $0 [-q] [-d]"
    echo ""
    echo "where:"
    echo "     -q: Query info"
    echo "     -d: delete info"
    echo ""
}

# Exit if no argument is passed in
: ${1?Usage}

while getopts "qd" opt; do
    case $opt in
        q)
            echo "Query info"
            ;;
        d)
            echo "Delete info"
            ;;
        *)
            Usage;
            exit 1
            ;;
    esac
done

Answer 1

What about this?

function Usage() {
    echo "Usage: $0 [-q] [-d]"
    echo ""
    echo "where:"
    echo "     -q: Query info"
    echo "     -d: delete info"
    echo ""
}

# Exit if no argument is passed in
: ${1?"$(Usage)"}

Anyhow, I think this is more readable:

if [ $# -lt 1 ] ; then
    Usage
fi

---

Another idea would be to handle it like this:

mode=""
while getopts "qdh" opt; do
    case $opt in
        q)
            mode="Query info"
            ;;
        d)
            mode="Delete info"
            ;;
        h)
            Usage
            exit 0
            ;;
        *)
            Usage >&2
            exit 1
            ;;
    esac
done

if [ -z "${mode}" ] ; then
    Usage >&2
    exit 1
fi

Answer 2

you just need pass argument to the bash script. assume that the bash script's name is hello.sh ; for example:

    #!/bin/bash
    # script's name is hello.sh
    : ${1?"Usage: $0 Argument"}
    echo hello,$1

then chmod a+x hello.sh

then we call the script use this : bash hello.sh yourname then echo the "hello,yourname" if you just called use bash hello.sh and no argument for this script you will get your error message like this Usage: hello.sh Argument