Tool to validate regex

Question

My goal is to validate regex for wildcard in domain addresses;

I've tried to do it through java.util.regex.Pattern, but some cases confuse me. Can someone explain, why it considered as valid pattern:

Pattern.compile("h]cat")

And this one as not valid:

Pattern.compile("h[cat")

Because it's interpreted from left to right. `[` opens a character class. And it's not closed. — Denys Séguret, Jul 15 '14 at 13:25
Your question isn't clear. Are you asking how to validate regular expressions ? Are you asking why you must escape the `[` ? — Denys Séguret, Jul 15 '14 at 13:27

score 2 · Accepted Answer · answered Jul 15 '14 at 13:25

2

h]cat in this string ] means a literal ] symbol.
h[cat in this string, a character class is started [ but without termination. So it's not valid. [ considered as start of char class.

answered Jul 15 '14 at 13:25

Avinash Raj

score 2 · Answer 2 · answered Jul 15 '14 at 13:26

2

It's a syntax thing. { and } can exist on themselves as literal, and so does ] when it's alone. An unclosed [ however, is syntax error.

answered Jul 15 '14 at 13:26

Unihedron

2 Answers2