How to use getopts in bash to parse script arguments?

Question

I have seen many examples for how to use getopts. But I know very basic of bash and I was not able to to implement it in my situation. I really appreciated if anyone expert can show me the template.

I have a script with minimum 6 and maximum 10 input. Here is a brief description:

script.sh -P passDir -S shadowDir -G groupDir -p password -s shadow

User must provide argument for -P -S -G and if not I must display usage and close the program. If argument are provided I need them to be saved into an appropriate variable.

But -p and -s is optional. However, if there is no -p I should do some tasks and if there is no -s I should do some other tasks and if none of them is there I should do some other tasks. Following is what I have written so far but it stock in the for loop.

#!/bin/bash

if [ "$(id -u)" != "0" ]; then
    echo "Only root may add a user to system"
    exit 2
else
    usage() { echo "Usage: $0 [-P <password file path>] [-S <shadow file path>] [-G <group path>]" 1>&2; exit 1; }
    passDir=""
    shadowDir=""
    groupDir=""
    while getopts ":P:S:G:" inp; do 
        case "${inp}" in
            P)
                $passDir = ${OPTARG};;
            S)  
                $shadowDir = ${OPTARG};;
            G)  
                $groupDir = ${OPTARG};;
            *)
                usage;;

         esac
    done

    echo "${passDir}"
    echo "${shadowDir}"
    echo "g = ${groupDir}"
fi

At the moment is user does not enter arguments nothing will be shown and if there is arguments it goes inside a loop!

John1024 · Accepted Answer · 2014-09-13 19:44:39Z

As I understand it, you are just missing some if statements to handle missing arguments. Consider:

usage() { echo "Usage: $0 [-P <password file path>] [-S <shadow file path>] [-G <group path>]" 1>&2; exit 1; }

if [ "$(id -u)" != "0" ]; then
    echo "Only root may add a user to system"
    exit 2
fi
passDir=""
shadowDir=""
groupDir=""
while getopts "P:S:G:" inp; do_
    case "${inp}" in
        P) 
            passDir=${OPTARG};;
        S)
            shadowDir=${OPTARG};;
        G)
            groupDir=${OPTARG};;
        *) 
            usage;;   
     esac
done

if  [ -z "$passDir" ] && [ -z "$shadowDir" ]
then
    # if none of them is there I should do some other tasks
    echo do some other tasks
elif ! [ "$passDir" ]
then
    # if there is no -p I should do some tasks_
    echo do some tasks
elif ! [ "$shadowDir" ]
then
    #if there is no -s I should do some other tasks
    echo do some other tasks
fi

Tom Fenech · Accepted Answer · 2014-09-13 18:37:27Z

2

I fixed a couple of things in your script. This works for me:

#!/bin/bash

if [ "$(id -u)" != "0" ]; then
    echo "Only root may add a user to system"
    exit 2
fi

usage() { echo "Usage: $0 [-P <password file path>] [-S <shadow file path>] [-G <group path>]" 1>&2
    exit 1 
}

passDir=""
shadowDir=""
groupDir=""
while getopts ":P:S:G:" inp; do 
    case "${inp}" in
        P)
            passDir=${OPTARG};;
        S)  
            shadowDir=${OPTARG};;
        G)  
            groupDir=${OPTARG};;
        *)
            usage;;

    esac
done

echo "p = $passDir"
echo "s = $shadowDir"
echo "g = $groupDir"

Assignments must not contain spaces: a=1 works, a = 1 doesn't
The variable name should not be prefixed with a $ in an assignment
If your if branch contains an exit statement, there's no need to put the rest of your code in the else branch

answered Sep 13, 2014 at 18:37

Tom Fenech

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2 Comments

Bernard Over a year ago

Thanks for your answer. I appreciate it. I chose other answer as solution because it explained solution for -s and -p is not provided. Thanks again

PM 2Ring Over a year ago

@Bernard : Now you have to add the cases for -p password and '-s shadow'. And don't forget to write a helpful usage message.

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