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Re^2: Detecting if a string is a regular expression

by LanX (Canon)
on Jan 12, 2013 at 11:03 UTC ( #1013030=note: print w/ replies, xml ) Need Help??


in reply to Re: Detecting if a string is a regular expression
in thread Detecting if a string is a regular expression

for completeness:

> Of course, that doesn't test if the metachars make sense as a regex

let's Perl parse Perl =)

$ perl -ple ' $_ = eval "sub { /$_/ }" ? "OK\n" : "$@" ' a OK a( Unmatched ( in regex; marked by <-- HERE in m/a( <-- HERE / at (eval 2 +) line 1, <> line 2. a[ Unmatched [ in regex; marked by <-- HERE in m/a[ <-- HERE / at (eval 3 +) line 1, <> line 3. a() OK

Cheers Rolf

UPDATE

unfortunately not always correct:

$ perl -ple ' $_ = eval "sub { /$_/ }" ? "OK\n" : "$@" ' a[$] OK

but

$ perl -e ' "abc" =~ /a[$]/ ' Unmatched [ in regex; marked by <-- HERE in m/a[ <-- HERE 5.010000/ at + -e line 1.

UPDATE

interesting, this happens because it's a run-time error ... (why?)

$ perl -e 'sub {"aaa" =~ /a[$]/}' $ perl -e '"aaa" =~ /a[$]/' Unmatched [ in regex; marked by <-- HERE in m/a[ <-- HERE 5.010000/ at + -e line 1. $ perl -ce '"aaa" =~ /a[$]/' -e syntax OK

looks like a parser problem for me!

UPDATE

variable interpolation is part of the problem, a[$] is a valid pattern, as long as it's not interpolated:

perl -E 'say q(a$) =~ q(a[$]) ' 1

UPDATE

this is very reliable

perl -ple ' $_ = eval "sub { 'a' =~ q\0$_\0 }" ? "OK\n" : "$@" '

to avoid problems with \0-delim consider using here-docs instead, or even a pack/unpack combination


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