Why does /i not seem to work

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

my $r="abc|xyz";
my $rx=qr($r);
my $c="XYZ";

my $x1=($c=~/$rx/i);
my $x2=(lc($c)=~/$rx/i);
say "\$x1=$x1";    
say "\$x2=$x2";
[download]

Results in:

$x1=

$x2=1

Shouldn't the /i give us a case insensitive match?

Perl version: This is perl 5, version 28, subversion 0 (v5.28.0) built for MSWin32-x64-multi-thread

Running on Windows 10

Am I missing something obvious>

TIA

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Re: Why does /i not seem to work by choroba (Cardinal) on Nov 21, 2019 at 15:47 UTC
Try examining the $rx: `(?^:abc\|xyz)` [download] The sequence `?^` is described in perlre: > Starting in Perl 5.14, a "^" (caret or circumflex accent) immediately after the "?" is a shorthand equivalent to "d-imnsx". Flags (except "d") may follow the caret to override it. But a minus sign is not legal with it. `-i` means the qr() by default creates case sensitive regex objects. `map{substr$_->[0],$_->[1]\|\|0,1}[\\|\|{},3],[[]],[ref qr-1,-,-1],[{}],[sub{}^ARGV,3]`	[reply] [d/l] [select]
Re: Why does /i not seem to work by Eily (Monsignor) on Nov 21, 2019 at 15:49 UTC
You can try this: `say $rx` to see what $rx is actually interpreted as. Spoiler, you'll see this:`(?^u:abc\|xyz)`. As documented in Extended Patterns: Starting in Perl 5.14, a "^" (caret or circumflex accent) immediately after the "?" is a shorthand equivalent to d-imnsx. Flags (except "d") may follow the caret to override it. But a minus sign is not legal with it. The ^ actually disables case insensitivity. That's because the qr operator "remembers" the flags used when creating a value with it, so that you can use it to always mean the same thing, regardless of where it's used. Three ways to solve your issue, use the /i when creating $rx: `$rx=qr/$rx/i;`. Use lc like you already did. Or do not use qr and keep the regex as a string. But that last one has some disavantages, using qr// will tell you if your regex is invalid sooner (if you use the regex in a completely different place, you might want the error message to be close to the definition, not the use), and it's not a bad thing to have something that is meant to be used as a regex to have the "type" Regexp.	[reply] [d/l] [select]
Re^2: Why does /i not seem to work by AnomalousMonk (Archbishop) on Nov 21, 2019 at 16:14 UTC
... keep the regex as a string ... has some disavantages ... Not least of which is that a `Regexp` object interpolates into another regex as an independent, quantifiable non-capturing group, and an interpolated string does not: `c:\@Work\Perl\monks>perl -wMstrict -le "my $rs = 'abc\|xyz'; my $rx = qr(abc\|xyz); ;; my $regex = qr( $rs+ $rx+ )x; print $regex; " (?x-ism: abc\|xyz+ (?-xism:abc\|xyz)+ )` [download] The two different representations can have very different effects when interpolated into a larger regex. Give a man a fish: `<%-{-{-{-<`	[reply] [d/l] [select]
Re: Why does /i not seem to work by LanX (Saint) on Nov 21, 2019 at 15:45 UTC
are you aware that the regex object has it's own flags? `DB<3> $r="abc\|xyz"; DB<4> $rx=qr($r); DB<5> p $rx (?^u:abc\|xyz)` [download] `DB<6> $rx=qr(/$r/i); # strike it, see update DB<7> p $rx (?^u:/abc\|xyz/i)` [download] update Sorry line 6 had the wrong syntax `DB<27> $rx = qr($r)i; # or traditionally qr/$r/i DB<28> p $rx (?^ui:abc\|xyz) DB<29> p "XYZ" =~ $rx 1` [download] Cheers Rolf _{(addicted to the Perl Programming Language :) Wikisyntax for the Monastery FootballPerl is like chess, only without the dice}	[reply] [d/l] [select]
Re: Why does /i not seem to work by perlpipe (Acolyte) on Nov 21, 2019 at 22:53 UTC
Thanks everyone. That was very informative.	[reply]


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Why does /i not seem to work

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