Your script works for me. Here's another way to do it.

#!/usr/bin/perl -l

BEGIN { require 5.005 }

use strict;
use warnings;
use autodie;
use IPC::Open3 qw(open3);

$| = 1;

open RPM, 'rpm -qa |';

my (@rpms) = <RPM>;
chomp @rpms;
@rpms = keys %{+{ map { $_ => 1; } @rpms } };
close RPM;

my(@glibc_rpm) = grep { /glibc/ } @rpms;
if (@glibc_rpm) {
    print "package found";
}
else {
    my ($writer, $reader, $err, $retCode);
    open3($writer, $reader, $err, `yum install glibc-common-2.5-49`);
    $retCode = <$reader>;
    $err = <$err>;
}
exit;
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