Well advice from TheHobbit is hard to beat. But in the interest of answering the question, try this code:

#!/usr/bin/perl
#Check password encryption 

$username  = shift || die "Usage $0 username plaintext_password\n";
$plaintext = shift || die "Usage $0 username plaintext_password\n";
$encpass    = (getpwnam($username))[1];
print "Testing encryption ... ";

if (crypt($plaintext, $encpass) ne $encpass) {
  print "FAILED\nTrying MD5 encryption ... ";
  if ( eval "use Crypt::PasswdMD5" ) {
    print "FAILED\n\nCannot try MD5 since Crypt::PasswdMD5 is not inst
+alled.\n";
  } else {
    if (&unix_md5_crypt($plaintext, $encpass) ne $encpass) {
      print "FAILED\n\nUnable to automatically use passwords from your
+ system.\n";
    } else {
      print "OK\n\nMD5 passwords were detected.\n";
    }
  }
} else {
  print "OK\n";
}
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