in reply to Re: Is there a way to make these two regex lines cleaner?
in thread Is there a way to make these two regex lines cleaner?

So, if you choose substitution: s/[^a-zA-Z0-9"' .?!-]//g

if transliteration (would be my choice): y/a-zA-Z0-9"' .?!-//cd

I'd still be inclined to escape the '-' in both cases: someone is all too likely to come along in a couple of years needing to add one more character to the allowed list, and the natural tendency would be to add it to the end.

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Re^3: Is there a way to make these two regex lines cleaner?
by AnomalousMonk (Archbishop) on Apr 17, 2022 at 22:55 UTC

    A hyphen placed at the beginning of a character class or tr/// search/replace list is also interpreted literally: 

    Win8 Strawberry 5.8.9.5 (32)  Sun 04/17/2022 18:43:19
C:\@Work\Perl\monks
>perl

use strict;
use warnings;

my $s = '123-abc-456';
$s =~ tr/-a-z//cd;
print "'$s' \n";

$s = '123-xyz-456';
$s =~ s/[^-a-z]//g;
print "'$s' \n";

^Z
'-abc-'
'-xyz-'

    [download]
    But one can argue that one is as likely to place new stuff at the start as at the end, so escaping remains wise. :)

    Give a man a fish:  <%-{-{-{-<

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Re^3: Is there a way to make these two regex lines cleaner?
by kcott (Archbishop) on Apr 18, 2022 at 04:40 UTC

    I've been putting '-' at the end for a very long time (probably decades) and have never encountered the scenario you describe; however, I'm not averse to a bit of defensive programming. :-)

    Update: The remainder of what I originally wrote is just wrong: I'll put it down to an idiotic brain fart. I've stricken it and, because it was quite long, removed it to a spoiler.

    Escaping the '-' in transliteration does not work; it'll actually remove '\' characters. Here's some additional code, for the script I provided above, to demonstrate this. 

    my $trans2 = '\\' . $str . '\\';
print "$trans2\n";
$trans2 =~ y/a-zA-Z0-9"' .?!\-//cd;
printf $fmt, 'TRANS2', $trans2;

    [download]

    Additional output:

    \*a%Z(5)-["'] <.?!>\
      TRANS2 : aZ5-"' .?!

    [download]

    See "perlop: Quote and Quote-like Operators" (first table indicates no interpolation) and, in "perlop: Quote-Like Operators", "y/SEARCHLIST/REPLACEMENTLIST/cdsr" (full details).

    Curiously, there seems to be a contradiction between what the documentation says and what I both expected and got. In "y/SEARCHLIST/REPLACEMENTLIST/cdsr" (my emphasis):

    "A hyphen at the beginning or end, or preceded by a backslash is also always considered a literal."

    That's from the 5.34.1 version of https://perldoc.perl.org/perl, I'm using 5.34.0, and clearly (from code and output) '\-' is being considered as two separate literals. I don't know if the documentation is simply wrong or, perhaps, badly worded and I'm misinterpreting it: I'd appreciate the thoughts of others with regard to this.

    — Ken

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