$ perl -lwMstrict
my $x="abcdefghi";
for (substr $x,1,3) {
  print;
  s/c/C/;
  print;
}
print $x;
my $y = \substr $x,5,3;
$$y=~s/g/G/;
print $x;
__END__
bcd
bCd
abCdefghi
abCdefGhi