Regex question - identify which pattern comes first

harangzsolt33 has asked for the wisdom of the Perl Monks concerning the following question:

I feel like I have learned a lot in the past 10 years since I started learning Perl, but I still probably don't know more than half of what's possible using regex. I have often come across situations where I needed to identify which pattern occurs first in a string. So, I am not trying to capture a part of the pattern nor am I trying to identify if it occurs at all or where. I am just trying to figure our which of the possible patterns is FIRST in the string. For example:

Sample string: "AB ABDA DCACCB AAA BSAA CAAB ACS ABA DBA BA DASSABACA 
+A"

I'm looking for either: BA[ABC]{2}  OR  CA[CD]{2}   OR   DA[SC]{2}

So, I would write: /BA[ABC]{2}|CA[CD]{2}|DA[SC]{2}/
[download]

Is there a way to get a return value of 1, 2, or 3 depending on which pattern was matched first? How would I do that?

Comment on Regex question - identify which pattern comes first Download Code

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Re: Regex question - identify which pattern comes first by ikegami (Patriarch) on May 02, 2026 at 01:53 UTC
`if ( /(BA[ABC]{2})\|(CA[CD]{2})\|(DA[SC]{2})/ ) my $first = ( defined( $1 ) ? 1 : defined( $2 ) ? 2 : 3 );` [download] `local our $first; / (?: BA[ABC]{2} (??{ $first = 1; }) \| CA[CD]{2} (??{ $first = 2; }) \| DA[SC]{2} (??{ $first = 3; }) /x;` [download]	[reply] [d/l] [select]
Re^2: Regex question - identify which pattern comes first by harangzsolt33 (Deacon) on May 02, 2026 at 02:15 UTC
Oh wow, that is an amazingly simple solution! Thank you so much!!! :-)	[reply]
Re^3: Regex question - identify which pattern comes first by LanX (Saint) on May 02, 2026 at 13:28 UTC
> that is an amazingly simple solution! Did you try it? These `(??{ $first = 1; })` won't work because they'll include 1,2 or 3 into the regex. Try `(?{ $first = 1; })`; with a single `?` instead. Cheers Rolf _{(addicted to the Perl Programming Language :) see Wikisyntax for the Monastery} Thus	[reply] [d/l] [select]