G'day catfish1116,

You could use the 'i' modifier. See "perlre: Modifiers".

You might also want to capture the exact variation matched so your subsequent print is more accurate; for instance, "... until I found perl", "... until I found Perl", "... until I found pErL", etc. See "perlre: Capture groups".

m/perl/i (Update: See https://perldoc.pl/perlre#Modifiers.)

It might also be useful to include some boundary assertions to avoid hitting on words like "perlaceous" or "properly" (untested):
    m{ (?i) \b perl \b }xms
(I prefer to use the inline (?i) rather than the /i modifier: I think it's more noticeable.)

last if m/\b(?:PERL|Perl|perl)\b/;
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# But I'm not a golfer.
use strict;
use warnings;
sub test {
    my ($m, $line) = (undef, 0);
    while ( <DATA> ) {
        $line++;
        last if (($m) = m/(perl)/i);
    }
    if ($m) {
        printf "There were %d lines until I found '%s'\n", $line, $m;
    } else {
        printf "I never found 'perl' in %d lines\n", $line;
    }
}
test
test
__END__
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This is peRl ok
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Relevant to the functionality but not to the OP's question:

Built-in variable $. is the number of lines read from the current (i.e. last-read) file handle. So:

while ( <> ) {
    last if m/perl/i;
}
print "There were $. lines until I found perl\n";
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