How to check if a string contains a substring in Bash

Question

I have a string in Bash:

string="My string"

How can I test if it contains another string?

if [ $string ?? 'foo' ]; then
  echo "It's there!"
fi

Where ?? is my unknown operator. Do I use echo and grep?

if echo "$string" | grep 'foo'; then
  echo "It's there!"
fi

That looks a bit clumsy.

Answer 1

You ought to recollect that shell prearranging is to a lesser degree a language and to a greater extent an assortment of orders. Instinctually you believe that this "language" expects you to follow an if with a [ or a [[. Both of those are simply orders that return a leave status showing achievement or disappointment (very much like each and every other order). Thus I'd utilize grep, and not the [ order.

Simply do:

in the event that grep - q foo <<<"$string";
    reverberation "It's there"
fi
Now that you are considering if as testing the leave status of the order that follows it (complete with semi-colon), why not reevaluate the wellspring of the string you are trying?

## Rather than this
filetype="$(file - b "$1")"
on the off chance that grep - q "tar document" <<<"$filetype";
#...

## Essentially do this
on the off chance that document - b "$1" | grep - q "tar chronicle";
#...
The - q choice makes grep not yield anything, as we just need the bring code back. <<< causes the shell to extend the following word and use it as the contribution to the order, a one-line variant of the << here record (I'm uncertain about whether this is standard or a Bashism).