BASH: Test whether string is valid

Question

Is there a way to invert this so that it checks if it is invalid first?

if expr "$string" : '-\?[0-9]\+$' >/dev/null
then
  echo "String is a valid integer."
else
  echo "String is not a valid integer."
fi

You don't need the [ ] to use !. You can type something like ! false right in the shell and see it succeeds. — Ben Jackson
– Ben Jackson, Commented Aug 8, 2011 at 20:00

shellter · Accepted Answer · 2011-08-08 20:40:34Z

6

Yes, I agree with @nobody and @BenJackson, all you need is to add the 'logical NOT' operator , i.e.

    if ! expr "$string" : '-\?[0-9]\+$' >/dev/null ; then
    #--^  right there ;-)
       echo "String is not a valid integer."
    else
       echo "String is a valid integer."
    fi

I hope this helps.

P.S. as you appear to be a new user, if you get an answer that helps you please remember to mark it as accepted, and/or give it a + (or -) as a useful answer.

answered Aug 8, 2011 at 20:40

shellter

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