search string bash code example

Example 1: checking if a substring exists in a string bash

string='Haystack';

if [[ $string =~ "Needle" ]]
then
   echo "It's there!"
fi

Example 2: substring if statement variable shell script

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

Example 3: substring if statement variable shell script

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