use strict;
use warnings;

sub bob
{
    if (!(my $t = shift)) {
        warn "data is false\n";
    } elsif ($t eq 'a') {
        warn "a\n";
    } elsif ($t eq '1') {
        warn "one\n";
    } else {
        warn $t;
    }
}

bob();
bob(1);
bob('a');
bob('c');

##</code><code>##

if (my $a = $c) {
    #...
} elsif (my $a = $b) {
    #...
}