Regex Mystery

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

Greetings monks,

It's late, I'm tired, and I must be missing the obvious. I need another pair of eyes to see what I've overlooked. The code sample below tests a file name against a regex containing the same file name. The first test uses forward slashes (and works as expected). The second test uses backslashes and does not work.

Please note: I have tried escaping the backslashes, but it still fails. I have tried running the regex through the "qr()" function, but it still fails. What am I missing here? TIA for any help you can provide.

#!/usr/bin/perl
use strict;
use warnings;

# WORKS
my $file  = 'C:/tmp';
my $regex = 'C:/tmp';
if ($file =~ m/$regex/i) {
    print "\nTest with forward slashes -- If stmt is true...\n";
}

# FAILS
$file  = 'C:\tmp';
$regex = 'C:\tmp';
if ($file =~ m/$regex/i) {
    print "\nTest with backslashes -- If stmt is true...\n";
}
[download]

"It's not how hard you work, it's how much you get done."

Comment on Regex Mystery Download Code

Replies are listed 'Best First'.
Re: Regex Mystery by tybalt89 (Monsignor) on Apr 13, 2025 at 04:20 UTC
`if ($file =~ m/\Q$regex/i) {` [download] because \t is a tab.	[reply] [d/l]
Re^2: Regex Mystery by roho (Bishop) on Apr 13, 2025 at 04:44 UTC
Thanks tybalt89. I knew it must be something obvious. Time to rest now. "It's not how hard you work, it's how much you get done."	[reply]
Re^2: Regex Mystery by harangzsolt33 (Deacon) on Apr 13, 2025 at 15:47 UTC
Wait, wouldn't this be more appropriate?: `if ($file =~ m/\Q$regex\E/i) ...`	[reply]
Re^3: Regex Mystery by Anonymous Monk on Apr 13, 2025 at 16:54 UTC
theyre exactly the same	[reply]
Re: Regex Mystery by InfiniteSilence (Curate) on Apr 13, 2025 at 04:26 UTC
`... # FAILS $file = 'C:\tmp'; $regex = qr~C:\\tmp~; if ($file =~ m/$regex/i) { print "\nTest with backslashes -- If stmt is true...\n"; }` [download] Prints... `Test with forward slashes -- If stmt is true... Test with backslashes -- If stmt is true...` [download] FYI coding while tired is a recipe for adding errors to code that you will find hard to find later. Celebrate Intellectual Diversity	[reply] [d/l] [select]
Re^2: Regex Mystery by choroba (Cardinal) on Apr 13, 2025 at 17:54 UTC
> FYI coding while tired is a recipe for adding errors to code that you will find hard to find later. But sometimes, coding while tired delivers at least something before the deadline. Life is hard. `map{substr$_->[0],$_->[1]\|\|0,1}[\\|\|{},3],[[]],[ref qr-1,-,-1],[{}],[sub{}^ARGV,3]`	[reply] [d/l]
Re^3: Regex Mystery by LanX (Saint) on Apr 13, 2025 at 19:15 UTC
There are various benefits of coding before sleep you get started you keep your sleeping brain busy with non social stuff you may wake up with a solution you may not contribute to the gene pool of the human race Cheers Rolf _{(addicted to the Perl Programming Language :) see Wikisyntax for the Monastery}	[reply]
Re^4: Regex Mystery by roho (Bishop) on Apr 14, 2025 at 04:54 UTC
Re^3: Regex Mystery by cavac (Prior) on Apr 18, 2025 at 13:39 UTC
But sometimes, coding while tired delivers at least something before the deadline. Yes, it does. Mostly the privilege of fielding support calls all weekend long, therefore pissing off the significant other. And the option to watch your favourite movies all night long, since you're gonna sleep on the couch anyway... PerlMonks XP is useless? Not anymore: XPD - Do more with your PerlMonks XP Also check out my sisters artwork and my weekly webcomics	[reply]
Re^2: Regex Mystery by roho (Bishop) on Apr 13, 2025 at 17:14 UTC
Thanks InfiniteSilence. You're right, working when tired produces diminishing returns. "It's not how hard you work, it's how much you get done."	[reply]
Re^3: Regex Mystery by cavac (Prior) on Apr 16, 2025 at 11:04 UTC
In my case, that would be negative returns. When i'm tired, i'm basically more productive doing nothing than when i'm touching code. Also, for a few hours after i'm forced by my body to take my pain meds for bad back (usually once a month on average). And being on the autistic spectrum, there are sometimes days my brain just refuses to do anything productive and i just can't concentrate on one singel thing for more than a minute or so.	[reply]