bash if string has substring 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: bash if substring

string='Hi substring' #To check if string has "Mylong" substring do
if [[ $string == *"substring"* ]]; then
  echo "String has substring"
fi

Example 3: bash substring test

#!/bin/bash

STR='GNU/Linux is an operating system'
SUB='Linux'

case $STR in

  *"$SUB"*)
    echo -n "It's there."
    ;;
esac