The easist explanation is that your open call fails. Since you don't check the return value, it does that silently.

open my $fh, '<', $configFile
   or die "Can't open '$configFile' for reading: $!";

my @allServers;

while (<$fh>) {
    push (@allServers, $_) if /^\w/;
}
close $fh or warn "Error while closing file: $!";
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