Question

I would like to check a string, so it only contains the characters 0-9 a-z -.

When I do

regex='[-a-z0-9]*'
string='abcd!'
if [[ $string =~ $regex ]]
then 
    echo "valid"
else
    echo "not valid"
fi

it outputs valid, where I would have expected not valid because $string contains a !.

Answer 1

try this: regex='^[-a-z0-9]*$'. It will force the complete line to match this class. Otherwise, only a single match, or no match at all (due to *) will return valid. ^...$ says the string starts and ends without anything that fails to match.