You could always abuse a module which already parses STDIN for key=value pairs:

$ cat sin.pl 
#!/usr/bin/env perl 
use strict;
use warnings;
use CGI::Lite 3.00;

my $cgi = CGI::Lite->new;
my $params = $cgi->parse_form_data;
$cgi->print_data;
$ cat myin.txt 
txtpatid=foo
txtpatpw=bar
txtpatserver=guest
$ ./sin.pl < myin.txt 
[ Reading query from standard input. Press ^D to stop! ]
txtpatid = foo
txtpatpw = bar
txtpatserver = guest
$
[download]

This isn't necessarily recommended - just showing that it's possible. YMMV.