How can I detect that no options were passed with getopts?

Question

I have this code -

#getoptDemo.sh
usage()
{
    echo "usage: <command> options:<w|l|h>"
}
while getopts wlh: option
do
    case $option in
            (w)
                    name='1';;
            (l)
                    name='2';;
            (h)
                    name='3';;
            (*)
                    usage
                    exit;;
    esac
done
print 'hi'$name

When I run bash getoptDemos.sh (without the option) it prints hi instead of calling the function usage. It calls usage when options other than w, h and l are given. Then can't it work when no options are specified.

I have tried using ?, \?, : in place of * but I can't achieve what I wanted to. I mean all the docs on getopt says it to use ?.

What am I doing wrong?

Solution 1

When you run this script without any options, getopt will return false, so it won't enter the loop at all. It will just drop down to the print - is this ksh/zsh?

If you must have an option, you're best bet is to test $name after the loop.

if [ -z "$name" ]
then
   usage
   exit
fi

But make sure $name was empty before calling getopts (as there could have been a $name in the environment the shell received on startup) with

unset name

(before the getopts loop)

Solution 2

getopts processes the options in turn. That's its job. If the user happens to pass no option, the first invocation of getopts exits the while loop.

If none of the options take an argument, the value of OPTIND indicates how many options were passed. In general, OPTIND is the number of arguments that are options or arguments to options, as opposed to non-option arguments (operands).

while getopts …; do …; done
if [ $OPTIND -eq 1 ]; then echo "No options were passed"; fi
shift $((OPTIND-1))
echo "$# non-option arguments"

In any case, you're not trying to determine whether there were no options, but whether none of the name-setting options were passed. So check if name is unset (and take care to unset it first).

Solution 3

I would check it with a variable. If getopts never passes the loop in case of no argument, you can use that for example like this:

#getoptDemo.sh
usage()
{
    echo "usage: <command> options:<w|l|h>"
}

no_args="true"
while getopts wlh: option
do
    case $option in
            (w)
                    name='1';;
            (l)
                    name='2';;
            (h)
                    name='3';;
            (*)
                    usage
                    exit;;
    esac
    no_args="false"
done

[[ "$no_args" == "true" ]] && { usage; exit 1; }

print 'hi'$name

Solution 4

If your script must receive option arguments is any case, place this block in the beginning (before getops).

if [[ ! $@ =~ ^\-.+ ]]
then
  #display_help;
fi

Block checks that parameter string not begins with - symbol, what indicates that first parameter is not an option argument.

View more solutions

Comments

[Admin]

What shell are you running it under?

[Admin]

I am running it under /bin/bash

[Admin]

Other alternatives: wiki.bash-hackers.org/howto/getopts_tutorial

[Hussain Tamboli]

no. its bash. So how do i achieve what I want - handle the no argument condition using bash.

[Yoshidk]

If you want a mandatory option, I don't think thats possible - its probably why they are called options :) You can test $name though, after the loop to make sure it has been set. if [ -z "$name" ] ; then usage; exit ; fi

[Hussain Tamboli]

thanks. the above code really helped. Its too bad getopts doesn't have such provision. What's worse than that is can't upvote you.

[Hussain Tamboli]

what if I was running other shell? zsh, sh. does any shell other than bash take care of this condition?

[Hussain Tamboli]

thanks. +1 for you. when I put the last 3 lines from your code in sample.sh and run bash sample.sh -abc file.txt it gives - 1 non-option arguments. how do I find out how many options were given. (here 3)

[Daniel]

Strange no one has commented on this slight bug -- if no options are given, OPTIND will be 1 after that 'while getopts ...' loop. Thus the if check should check equality with 1, not zero.

[Vincent Gerris]

you need to remove the () behind the usage call