Apple
Pear
Apple
Pear

Apple
Pear
Grape
Apple
Pear
Grape

perl -pe 's/PearK/nGrape/' file1.txt

perl -pe '$_ .= "Grapen" if /Pear/' file

open(DATA,"<test1") or die "No test1 file";
while($data = <DATA>){
    if($data =~ /Pear/){
        $data = $data . "Grapen";
    }
    print "$data";
}