You can code exactly like that in Perl, thanks to the /x modifier. It allows you to insert comments inside the regexp.

$callerid =~ / # we want to match
             ( # and remember
             . # any character
           {7} # 7 times
             ) # stop remembering
             $ # then the end of line
             /x; # and that's the end of the match

In this particular case, this is overkill, but in some cases, it can be very useful in more cmoplicated situations.

And as all others in this thread have said, I too recommend using substr.