String contains in bash

string=`echo My string`

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

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

string='My string';

if [[ $string == *My* ]]
then
  echo "It's there!";
fi

case "$string" in
  *foo*)
    # Do stuff
    ;;
esac

string='My string';

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

if [ "$string" != "${string/foo/}" ]; then
    echo "It's there!"
fi

if grep -q foo <<<$string; then
    echo "It's there"
fi

text="   <tag>bmnmn</tag>  "
if [[ "$text" =~ "<tag>" ]]; then
   echo "matched"
else
   echo "not matched"
fi

str=this_is_my_string
if [ `expr match "$str" ".*my.*"` != "0" ]; then
  echo "there";
fi;

expr "$variable" : 'regex'

if [ "$string" != "${string/foo/}" ]; then echo "It's there!" fi

[ $(expr $mystring : ".*${search}.*") -ne 0 ] && echo 'yes' ||  echo 'no'

[ $(expr $mystring : ".*${search}.*") -ne 0 ] && echo 'yes' ||  echo 'no'