Regex to match ascending sequence

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

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Re: Regex to match ascending sequence by LanX (Saint) on Oct 15, 2015 at 16:43 UTC
Second statement: assign regex to $c Inside regex: increment $c what do you expect from an incremented regex? Then your regex says `greedy match ( any number or $c++ )` and number will match any time before trying the `or` branch. Actually this might be the reason why incrementing a regex doesn't throw an error, it's never executed. Cheers Rolf _{(addicted to the Perl Programming Language and ☆☆☆☆ :) Je suis Charlie!}	[reply] [d/l] [select]
Re^2: Regex to match ascending sequence by ExReg (Priest) on Oct 15, 2015 at 16:46 UTC
Sadly true. Indication that at this point I am flailing at trying to figure out how to do it.	[reply]
Re: Regex to match ascending sequence by Eily (Monsignor) on Oct 15, 2015 at 16:59 UTC
What did you expect $c++ to do, knowing that the first time the code is run the value of $c is the current regular expression ? Anyway, here is something that should do what you want: `'234565432' =~ / (\d) (?{ $c = $1}) # Match the first number and initialize $c (?: (??{ ++$c }) # Same as the previous char + 1 )*/x; print $&;` [download]	[reply] [d/l]
Re^2: Regex to match ascending sequence by ExReg (Priest) on Oct 15, 2015 at 17:19 UTC
Saints be praised! OK, maybe Curates be praised! It works. And it makes sense. Can't beat that. I can feel scales of ignorance falling off my eyes as I type.	[reply]
Re^2: Regex to match ascending sequence by Anonymous Monk on Oct 15, 2015 at 17:24 UTC
Try 148012 :)	[reply]
Re^3: Regex to match ascending sequence by LanX (Saint) on Oct 15, 2015 at 22:45 UTC
> Try 148012 :) This should do `my $regex = qr/ \d (??{ substr($&, -1) + 1 }) + /x; "148012" =~ $regex; print ">$&<" __END__ >012<` [download] The minimal length of the sequence can be set by `{x,}` instead of the `+` quantifier. š Cheers Rolf _{(addicted to the Perl Programming Language and ☆☆☆☆ :) Je suis Charlie!} š) with x = min-1	[reply] [d/l] [select]
Re^4: Regex to match ascending sequence by ExReg (Priest) on Oct 16, 2015 at 14:41 UTC
Re^5: Regex to match ascending sequence by LanX (Saint) on Oct 16, 2015 at 18:19 UTC
Re^3: Regex to match ascending sequence by ExReg (Priest) on Oct 15, 2015 at 17:35 UTC
I think that it is to be expected with left-most, longest. It would find the 1, not find a 2 after it and quit, without seeing that there is a 012 later.	[reply]
Re: Regex to match ascending sequence by Laurent_R (Canon) on Oct 15, 2015 at 16:40 UTC
In your regex, I guess that `\d*` will match the whole string so that the other part of the alternation is just short circuited.	[reply] [d/l]
Re: Regex to match ascending sequence by LanX (Saint) on Oct 15, 2015 at 17:02 UTC
This works for me `my $regex = qr# (\d) (??{ my $c //= $1 ; ++$c })+ #x; "2345654321" =~ $regex; print $&;` [download] Cheers Rolf _{(addicted to the Perl Programming Language and ☆☆☆☆ :) Je suis Charlie!}	[reply] [d/l]
Re^2: Regex to match ascending sequence by ExReg (Priest) on Oct 15, 2015 at 17:27 UTC
Unfortunately, when I try this on my Perl 5.8, I get a panic: top_env message. I know that it doesn't have the //= operator.	[reply]
Re^3: Regex to match ascending sequence by Laurent_R (Canon) on Oct 15, 2015 at 22:31 UTC
`$c //= $d;` [download] is just syntactic sugar for various constructs such as: `$c = defined $c ? $c : $d;` [download] or `$c = $d unless defined $c;` [download] Update: I've just quickly tried on an old VMS platform with Perl 5.8.6 with this regex definition: `$regex = qr# (\d) (??{ my $c = $1 unless defined $c; ++$c })+ #x;` [download] it still does not seem to work.	[reply] [d/l] [select]
Re^3: Regex to match ascending sequence by LanX (Saint) on Oct 15, 2015 at 18:14 UTC
The Defined-Or operator is best emulated with `defined` and `or` No idea about scopes in 5.8 , I remember 5.10 (or 5.12 ?) having an issue in this case. Cheers Rolf _{(addicted to the Perl Programming Language and ☆☆☆☆ :) Je suis Charlie!}	[reply]
Re^3: Regex to match ascending sequence by Anonymous Monk on Oct 15, 2015 at 17:30 UTC
Try `local our $c;` Also, 5.8 is too old for experimental regex features	[reply] [d/l]
Re^4: Regex to match ascending sequence by ExReg (Priest) on Oct 15, 2015 at 17:38 UTC
Re: Regex to match ascending sequence by Anonymous Monk on Oct 15, 2015 at 16:49 UTC
`perl -le '"2345654321" =~ /(0?1?2?3?4?5?6?7?8?9?)/ and print $1'` [download] snicker :)	[reply] [d/l]
Re^2: Regex to match ascending sequence by ExReg (Priest) on Oct 15, 2015 at 16:57 UTC
That works for what I stated, but not for what I _meant_. It would match 1357, but I would want it to match 1234567. Also, I am looking for a dynamic regex to do this. The whole reason for all this is that I am trying to get a grasp on dynamic regexes (??{}) and thought this would be an easy start.	[reply]