When i change the code from
$cnf{$c}=$_;
to 
push @{$cnf{$c} }, $_;
It doesn't work.

##</code><code>##

#!/usr/bin/perl

use strict;
use warnings;
use Data::Dumper;

my @fields=split /\n/, <<'.END';
"INVITE sip:paka@36.212.176.92 SIP/2.0
To:samir <sip:paka@36.212.176.92>
Via: SIP/2.0/udp 36.212.176.90:5060;branch=z9hG4bk_Vn
Via: SIP/2.0/udp 36.212.176.66:5060;branch=z9hG4bk_oo
From: sanjay<sip:sanjay@36.212.176.90>
Call-ID: _Vn8TZTk2H@36.212.176.90 
CSeq: 215 INVITE
Max-Forwards: 70
Contact: sanjay<sip:sanjay@36.212.176.90:5060>";
.END

my %config = (
    URI =>           { regex => qr/^INVITE\ssip:/},
    To =>            { regex => '^To:'},
    From =>          { regex => '^From:'},
    Via =>           { regex => '^Via:'},
    Call_ID =>       { regex => '^Call-ID:'},
    CSeq =>          { regex => '^CSeq:'},
    MaxForwards =>   { regex => '^Max-Forwards:'},
    Contact =>       { regex => '^Contact:'},
);

my %cnf;
foreach (@fields) {
    foreach my $c (keys %config) {
        if (/$config{$c}{regex}/) {
            push @{ $cnf{$c} }, $_;
        }
    }
}

print Dumper $cnf{Via};

__END__