#! /usr/bin/perl
use warnings;
use strict;

my @strings = ('4;T;X;15;O20;O26.0;O26.0;O260;Excessive weight gain in pregnancy;242;UNDEF;UNDEF;2-067;1-089',
               '4;T;X;15;O20;O26.1;O26.1;O261;Low weight gain in pregnancy;242;UNDEF;UNDEF;2-067;1-089');

for my $string (@strings) {
    my $text = (split /;/, $string)[8];
    print $text, "\n" if $text =~ /weight gain/;
}