pos
See the current Perl documentation for pos.
Here is our local, out-dated (pre-5.6) version:
pos - find or set the offset for the last/next m//g search
pos SCALAR
pos
Returns the offset of where the last m//g
search left off for the variable is in question ($_
is used when the variable is not specified). May be modified to change that
offset. Such modification will also influence the \G
zero-width assertion in regular expressions. See the perlre manpage and
the perlop manpage.