if substring in 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: bash substring test

#!/bin/bash

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

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

Example 3: substring if statement variable shell script

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

Example 4: substring if statement variable shell script

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

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