If you're doing a lot of these tests for different values of "abc", I'd suggest just trimming the whitespace once and then working with the trimmed string:

# ...

use String::Trim;

while(<>) {
    trim;

    given($_) {
        when("abc") {
            say "Got 'abc'!";
        }
        when("cmc") {
            say "Got 'cmc'!";
        }
        when("uep") {
            say "Got 'uep'!";
        }
    }
}
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If you're looking to do more complicated processing that nonetheless involves a lot of boilerplate, you could build a list of regular expressions on-the-fly:

sub got_abc {
    say "Got 'abc'!";
}

sub got_cmc {
    say "Got 'cmc'!";
}

sub got_uep {
    say "Got 'uep'!";
}

sub got_a3 {
    say "Got 'a{3}'!";
}

my %interesting = (
    "abc"       => \&got_abc,
    "cmc"       => \&got_cmc,
    "uep"       => \&got_uep,
    "a{3}"      => \&got_a3,
);

# add boilerplate
my %tests = map {
        qr/^\s*$_\s*$/ => $interesting{$_}
    } keys %interesting;

# process data and apply tests
while(<>) {
    chomp;

    foreach my $test (keys %tests) {
        $_ =~ $test and &{ $tests{$test} };
    }
}
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