bash substring regex matching wildcard

Question

I am doing bash , i try to test if the substring "world" in the given variable x. I have part of code working. But the other one not working. I want to figure out why

First one is working

x=helloworldfirsttime
world=world
if [[ "$x"  == *$world* ]];then
    echo matching helloworld

Second one is not working

x=helloworldfirsttime
if [[ "$x"  == "*world*" ]];then
    echo matching helloworld

How to make second one work without using variable like the 1st method

Can someone fix the second one for me.. thanks

Answer 1

Just remove the quotes:

x=helloworldfirsttime
if [[ "$x" == *world* ]]; then
    echo matching helloworld
fi

Note that this isn't regex (a regex for this would look something like .*world.*). The pattern matching in bash is described here:
http://www.gnu.org/software/bash/manual/html_node/Pattern-Matching.html

Answer 2

x=helloworldfirsttime
$ if [[ "$x" == *world* ]]; then echo MATCHING; fi
MATCHING

This works because bash's builtin [[ operator treats the right-hand-side of an == test as a pattern:

When the == and != operators are used, the string to the right of the operator is used as a pattern and pattern matching is performed.