Simple way to skip spaces and # comments

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

I parse string using /gc and \G regexes. Current solution for skipping white characters and comments starting from # to the end of line is:

$$a =~ /\G(?=(\s|#))(?:\s++|#.*+)++/gc;

Look ahead ?= assertion is necessary, because zero-length matches cause problems. That solution unfortunatelly gives error:

Complex regular subexpression recursion limit (32766) exceeded

I have changes to such one:

while ($$a =~ /\G(?:\s++|#.*+)/gc) {};

but this is not elegant. I have changed "+" to "*" after "\s" and this also solves the problem, but I don't know why...

$$a =~ /\G(?=(\s|#))(?:\s*+|#.*+)++/gc;

Questions: (1) what is the better solution to strip white chars and commments (2) why * instead of + solves the problem?

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Re: Simple way to skip spaces and # comments by ikegami (Patriarch) on Jul 31, 2020 at 14:18 UTC
Treat "`#`" and the following characters as a single whitespace character. `/\G (?: \s \| \# .* )++ /xgc` [download] More efficient? `/\G (?: \s++ \| \# .*+ )++ /xgc` [download]	[reply] [d/l] [select]
Re^2: Simple way to skip spaces and # comments by leszekdubiel (Scribe) on Jul 31, 2020 at 14:36 UTC
`/\G (?: \s++ \| \# .+ )++ /xgc` ^^^^ This makes error about recursion limit... # for f in `seq 40123`; do echo " #alfa beta"; done \| perl -e 'use str +ict; use warnings; undef $/; my $s = <STDIN>; print length $s, "\n"; +$s =~ /\G (?: \s++ \| \# .+ )++ /xgc; print pos $s, "\n"; ' 481476 Complex regular subexpression recursion limit (32766) exceeded at -e l +ine 1, <STDIN> chunk 1. 196597 [download]	[reply] [d/l] [select]
Re^3: Simple way to skip spaces and # comments by ikegami (Patriarch) on Jul 31, 2020 at 14:42 UTC
If certain things are expected to match more than 32766 times, you need to break it down. So if the following exceeds the limit, `a+` [download] you have to use `(?:a{1,32766})+` [download] So, `/\G (?: \s++ \| \# .+ )++ /xgc` [download] becomes `/\G (?: (?: \s++ \| \# .+ ){1,32766}+ )+ /xgc` [download] Or maybe even `/\G (?: (?: (?: \s{1,32766}+ )++ \| \# (?: .{1,32766}+ )*+ ){1,32766}+ )+ /xgc` [download]	[reply] [d/l] [select]
Re: Simple way to skip spaces and # comments by perlfan (Vicar) on Jul 31, 2020 at 11:28 UTC
I usually just `s///` that kind of thing, `my $line = 'valid text blah blah # delete me and everything after poun +d # also this'; $line =~ s/#.*$//; print qq{"$line"\n};` [download] results in: `"valid text blah blah "` [download] I don't have an answer for your #2 question at the end.	[reply] [d/l] [select]
Re^2: Simple way to skip spaces and # comments by leszekdubiel (Scribe) on Jul 31, 2020 at 13:56 UTC
To be more precise... `$a` is a reference to string, that is beeing parsed. `pos $$a` shows current parsing position. From that position I need to skip all spaces and comments that extend maybe on many lines in that string. Positve zero-length match should be avoided.	[reply] [d/l] [select]
Re^3: Simple way to skip spaces and # comments by perlfan (Vicar) on Jul 31, 2020 at 16:24 UTC
>Questions: (1) what is the better solution to strip white chars Asked and answered. Ż\_(ツ)_/Ż	[reply]


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