--- put your name value pairs inside a text file eg. v.txt

a=20
b=30
arg=40

If t.pl is your script then execute as t.pl  < v.txt

sample :

use CGI;
my $page=new CGI ;
if (! $page->param() )
        {
        print ".. will NOT read from STDIN\n";
        }
        else
        {
        print ".. will read from STDIN\n";
        foreach ( $page->param () )
                {
                print "$_ = @{[$page->param ($_)]}\n";
                }
        }
[download]

results:

(offline mode: enter name=value pairs on standard input)
.. will read from STDIN
a = 20
y = 30
arg = 40

Note: for more powerful solutions you may want to look at how the function read_from_cmdline in CGI.pm is used and called and what it does.