How to check if a string contains a specific character

Question

I've been trying to make a condition in a bash script which will tell me if the given string contains chars other than letters or a hyphen.

i.e, this is a legal string: hello-world

and that one is not: hello-123-there

This is what I have tried so far but I think I also have a logic mistake:

if ! [[ "$1" == *-* ]] && ! [[ "$1" =~ ^[a-zA-Z]+$ ]] ; then
        echo "the line is bad"
        exit
fi

(while $1 refers to the string, of course). Would love to get some help from you.

anubhava · Accepted Answer · 2013-12-19 16:39:52Z

3

You can use regex features of BASH:

[[ "$str" =~ ^[a-zA-Z-]*$ ]] && echo "valid" || echo "invalid"

OR using glob:

[[ "$str" == *[^-[:alpha:]]* ]] && echo "invalid" || echo "valid"

Which is same as:

if [[ "$str" =~ ^[a-zA-Z-]*$ ]]; then
    echo "valid"
else
    echo "invalid"
fi

answered Dec 19, 2013 at 15:44

anubhava

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4 Comments

thanks, but - i dont understand the "&&" and "||" usgae, can you plz write the condition? thanks.

Is this what you're looking for?

Plain glob patterns work too: [[ $str == *[^-[:alpha:]]* ]] && echo invalid

That's correct @glennjackman. Thanks editing the answer with this option as well.