if (uc $error eq "ERROR"){
   # . . .
}

##</code><code>##

if (lc $error eq "error"){
   # . . .
}

##</code><code>##

#!/usr/bin/perl

use strict;
use warnings;
use Benchmark qw/:all :hireswallclock/;

my $test_str='error';
my @test=map {
    my @chr=("\0", " ");
    local $_=$test_str;
    s/./$& ^ $chr[rand 2]/ge} 1..100;

no warnings 'void';
cmpthese -30, { regex => sub { /^\Q$test_str\E$/i for @test },
                lc => sub { $test_str eq lc for @test} }, 'all';

__END__

##</code><code>##

Benchmark: running lc, regex for at least 30 CPU seconds...
        lc: 34.068 wallclock secs (34.10 usr  0.00 sys +  0.00 cusr  0.00 csys = 34.10 CPU) @ 19917.24/s (n=679178)
     regex: 31.518 wallclock secs (31.53 usr  0.00 sys +  0.00 cusr  0.00 csys = 31.53 CPU) @ 13689.50/s (n=431630)
         Rate regex    lc
regex 13690/s    --  -31%
lc    19917/s   45%    --

##</code><code>##

Benchmark: running lc, regex for at least 30 CPU seconds...
        lc: 31.4462 wallclock secs (31.45 usr  0.00 sys +  0.00 cusr  0.00 csys = 31.45 CPU) @ 26138.57/s (n=822058)
     regex: 31.8579 wallclock secs (31.86 usr  0.00 sys +  0.00 cusr  0.00 csys = 31.86 CPU) @ 14326.49/s (n=456442)
         Rate regex    lc
regex 14326/s    --  -45%
lc    26139/s   82%    --