##
P:\test>perl -wl
my $a = 'a' x 10;
my $b;
$b .= substr( $a, $_, 10-$_ ) . '-' x $_ for 0 .. 9;
print $b;
^Z
aaaaaaaaaaaaaaaaaaa-aaaaaaaa--aaaaaaa---aaaaaa----aaaaa-----aaaa------aaa-------aa--------a---------
##
##
P:\test>perl -wl
my $a = 'a' x 10;
my $b .= substr( $a, $_, 10-$_ ) . '-' x $_ for 0 .. 9;
print $b;
^Z
Use of uninitialized value in print at - line 3.