Regex: Lazy matching in nested match group

Question

I'm having problems with the following Regex:

I login with (CORRECT|INCORRECT (username|password|username and password)) credentials

Basically, what I want it to match is the following 4 strings only (which it does):

I login with CORRECT credentials
I login with INCORRECT username credentials
I login with INCORRECT password credentials
I login with INCORRECT username and password credentials

However, the match groups are as follows:

1: CORRECT 2:
1: INCORRECT username 2: username
1: INCORRECT password 2: password
1: INCORRECT username and password 2: username and password

I want the match groups as follows:

1: CORRECT
1: INCORRECT 2: username
1: INCORRECT 2: password
1: INCORRECT 2: username and password

Try (?| for the outer group so that it numbers subpatterns based on which option is matched. — Niet the Dark Absol
– Niet the Dark Absol, Commented Sep 6, 2016 at 17:24

score 1 · Accepted Answer · 2016-09-06 18:19:58Z

If you can use an engine that supports Branch Reset it can be done like this

I login with (?|(CORRECT)()|(INCORRECT) (username(?: and password)?|password)) credentials

The group numbering is reset on each alternation in the branch reset group:

 I [ ] login [ ] with [ ] 
 (?|                           # Branch reset
      ( CORRECT )                   # (1)
      ( )                           # (2)
   |                              # or,
      ( INCORRECT )                 # (1)
      [ ] 
      (                             # (2 start)
           username 
           (?: [ ] and [ ] password )?
        |  
           password
      )                             # (2 end)
 )                             # End branch reset
 [ ] credentials

Or, if branch reset is unavailable use this

I login with (?:(CORRECT)|(INCORRECT) (username|password|username and password)) credentials

What this does is capture correct/incorrect in separate groups, then
if group 2 matched, group 3 is valid.
It still matches the exact same strings.

 I[ ]login[ ]with[ ]
 (?:
      ( CORRECT )                   # (1)
   |  ( INCORRECT )                 # (2)
      [ ]
      ( username | password | username[ ]and[ ]password )  # (3)
 )
 [ ]credentials

anubhava · Accepted Answer · 2016-09-06 17:29:49Z

0

You don't need nested groups, you can use this regex with fixed first group and an optional 2nd group:

I login with ((?:IN)?CORRECT) (?:(username|password|username and password) )?credentials

RegEx Demo

answered Sep 6, 2016 at 17:29

anubhava

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1 Comment

user557597 Over a year ago

The problem is if the OP requires only CORRECT credentials, because that's how he set up his regex.

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