use strict;
use warnings;
use 5.010;

my $port_name = 'sdm_yout_i[1]';

$port_name =~ s/\[|\]/\\$&/g; # escaping [ and ]

while (<DATA>)
{
    if  ( /\.[0-9a-z_]+ \( {${port_name}.+?\)/ ) {
        print '$port_name = ' ; say $port_name;
        print 'cell name = ' ; say $&;
    }
}

__DATA__
.dout_sar ( dout_sar ) , .dcoc_status ( dcoc_status ) , .sdm_yout_i ( {sdm_yout_i[1] , n145 } ) , .sdm_yout_q ( sdm_yout_q )