Meaning of "=~" operator in shell script

Question

I came across a shell script where the code is

for line in $LIST_ARRAY;do
if [[ $LIST_ARRAY =~ $line ]]
then
echo "true"
....
...
.

What is the use of =~ in this case?

Solution

it's the Equal Tilde operator that allows the use of regex in an if statement.

An additional binary operator, =~, is available, with the same precedence as == and !=. When it is used, the string to the right of the operator is considered an extended regular expression and matched accordingly (as in regex(3)). The return value is 0 if the string matches the pattern, and 1 otherwise. If the regular expression is syntactically incorrect, the conditional expression's return value is 2. If the shell option nocasematch is enabled, the match is performed without regard to the case of alphabetic characters. Any part of the pattern may be quoted to force it to be matched as a string.

http://linux.die.net/man/1/bash