$_ = "abcdmefg";
$_ = /m/;
print "$&\t$`\t$'\n";

##</code><code>##

It prints:     m   abcd   efg

##</code><code>##

$_ = "abcdmefg";
while(m/m/g)
{
   print "matched 'm' at ",pos,"\n";
}