Question

How do I search for a string that contains only chars from a set including x, and require it to contain x? e.g. [a-z]+ but not matching if it doesn’t contain x.

So it should match quux but not foo or bar.

Answer 1

Assuming you want to match a string of only x,y or z, match start (^) followed by zero or more y or z ([yz]*) followed by an x followed by zero or more x, y or z ([xyz]*) followed by end ($)

^[yz]*x[xyz]*$

If you are trying to match [a-z] but with an x in there somewhere, then this should do it

^[a-z]*x[a-z]*$