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Re^3: Regex to detect file nameby kcott (Archbishop) |
on Jul 07, 2018 at 05:14 UTC ( [id://1218078]=note: print w/replies, xml ) | Need Help?? |
G'day AnomalousMonk, With regard to the POSIX character class, ++hippo has already pointed out the problem with that. You can certainly be forgiven for that because the documentation appears to be wrong. From "perlrecharclass: POSIX Character Classes":
I rarely use the POSIX classes and wasn't aware of that discrepancy. Anyway, while possibly "easier on the eye", that's likely to result in a fair amount of frustration for someone attempting to perform debugging and assuming the documentation is correct. The problem could be further exacerbated when input characters may not appear to be ones that should be failing. While hippo's example using "LATIN SMALL LETTER C WITH CEDILLA" (ç) was fairly obvious, the glyphs for some characters (depending on the font) may be identical or so similar that it's difficult to tell them apart. Consider "LATIN CAPITAL LETTER A" (A) and "GREEK CAPITAL LETTER ALPHA" (Α): $ perl -C -E ' use utf8; say "$_ (", ord $_, "): ", /\A[A-Za-z0-9]\z/ ? "✓" : "✗" for qw{A Α} ' A (65): ✓ Α (913): ✗ $ perl -C -E ' use utf8; say "$_ (", ord $_, "): ", /\A[[:alnum:]]\z/ ? "✓" : "✗" for qw{A Α} ' A (65): ✓ Α (913): ✓ As far as the 'x' modifier goes, I don't disagree that it can improve readability; however, where it's felt necessary to use it — either because the regex is particularly complex or it's code that junior developers will need to deal with — spreading the regex across multiple lines and including comments might be even better:
And, with 5.26 or later, perhaps even clearer as:
We've already had exhaustive discussions about the 'm' and 's' modifiers. Use them if you want to follow PBP suggestions but understand that they do absolutely nothing here: there's no '^' or '$' assertions that 'm' might affect; there's no '.' (outside a bracketed character class) that 's' might affect. — Ken
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