I have one file file.xml.
and I am trying to modify the text of tag h<ref> if it's attribute value is cde.

<?xml version='1.0'?>

<root>

  <test>

    <name>file</name>

    <href attr="abc">saur</href>

  </test>

  <test>

    <name>file1</name>

    <href attr="cde">mand</href>

  </test>

</root>

I have written a code as:

use XML::Twig;

use Data::Dumper;


my $xml=$ARGV[0];

my $tag_name=$ARGV[1];

my $att_name=$ARGV[2];

my $att_value=$ARGV[3];

my $tag_text=$ARGV[4];

my $twig = XML::Twig->new(twig_roots => {$tag_name =>  \&select_change},
               );


$twig->parsefile_inplace($xml);

$twig->flush;


sub select_change

{

    my($twig,$tag_name)=@_;

    if ($tag_name->att('$att_name') =~ "$att_value")

    {

        $tag_name->set_text('$tag_text');

    }

}

Now I am giving command line as 
perl -w twigparse.pl file.xml href attr cde sriram
Now it is not running but if I give values to all command line variables in program then it runs.Please correcr me.I am stuck in this code...Help me........