$str= "bbbcccbbb"
while( $str =~ /b*/g ) { print "($`)<$&>($')\n" }
__END__
()<bbb>(cccbbb)
(bbb)<>(cccbbb) <-- This one
(bbbc)<>(ccbbb)
(bbbcc)<>(cbbb)
(bbbccc)<bbb>()
(bbbcccbbb)<>() <-- This one

##</code><code>##

a
bbbcccbbb
.
s/(b*)/x\1/g

##</code><code>##

xbbbcxcxcxbbb
   /\       /\ no "x"s there