ne vs. ! eq

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

Hey Monks I never realized perl behaves like this. There is a difference between (! 'a' eq 'b') and ('a' ne 'b').

#!perl
use strict;
use warnings;
use Data::Dumper;

my $s1 = 'bla';
my $s2 = 'blu';

my $r = $s1 eq $s2;
print Dumper $r;

if (! $s1 eq $s2) {
    print "$s1 and $s2 are not the same\n";
}
else {
    print "$s1 and $s2 are the same\n";
}

exit 0;
[download]

prints:

$VAR1 = '';
bla and blu are the same
[download]

The "correct" ($s1 ne $s2) works as expected. But why does (! $s1 eq $s2) not work?

Probably there is a simple explanation but I don't know it... Maybe one of you Monks can explain this.

Thank you

Comment on ne vs. ! eq Select or Download Code

Replies are listed 'Best First'.
Re: ne vs. ! eq by haukex (Archbishop) on Feb 25, 2020 at 13:38 UTC
Precedence. See perlop: `! $s1 eq $s2` is the same as `(!$s1) eq $s2`, and not `!( $s1 eq $s2 )`, as B::Deparse will tell you: `$ perl -MO=Deparse,-p -e 'if (! $s1 eq $s2) {}' if (((!$s1) eq $s2)) { (); }` [download] You'll need to write either `if ( !( $s1 eq $s2 ) )`, `if ( not $s1 eq $s2 )`, `unless ( $s1 eq $s2 )`, or of course `if ( $s1 ne $s2 )`.	[reply] [d/l] [select]
Re^2: ne vs. ! eq by boerni (Novice) on Feb 25, 2020 at 13:42 UTC
Thank you very much haukex!	[reply]
Re: ne vs. ! eq by LanX (Saint) on Feb 25, 2020 at 19:54 UTC
Just wanted to add: That's a good demo to highlight why Perl has two boolean negations: `not` and `!` Cheers Rolf _{(addicted to the Perl Programming Language :) Wikisyntax for the Monastery}	[reply] [d/l] [select]