use warnings;
use strict;
use Test::More;

my $string=qq{parameter=TO_DATE('1900-01-01','YYYY-MM-DD')\n};

my $REGEX = qr{^ (\w+) = (?| "(.+)" | ( (?!").+(?<!") ) ) (\n|\z) }x;
if ( $string =~ $REGEX ) { $string = qq{$1="$2"$3} }
else { die "failed to parse $string" }

is $string, qq{parameter="TO_DATE('1900-01-01','YYYY-MM-DD')"\n};

done_testing;