bash script check if string contains code example

Example 1: check if variable contains string bash

STRING='Hello world'
if [[ $STRING =~ "Hello" ]] ; then echo "It's here" ; fi

Example 2: bash substring test

#!/bin/bash

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

if grep -q "$SUB" <<< "$STR"; then
  echo "It's there"
fi

Example 3: bash substring test

#!/bin/bash

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

if [[ "$STR" =~ .*"$SUB".* ]]; then
  echo "It's there."
fi