s/PATTERN/REPLACEMENT/egimosx
 
 [ ... snip ...]

               Any non-alphanumeric, non-whitespace delimiter may
               replace the slashes.  If single quotes are used,
               no interpretation is done on the replacement
               string (the /e modifier overrides this, however).
               Unlike Perl 4, Perl 5 treats backticks as normal
               delimiters; the replacement text is not evaluated
               as a command.  If the PATTERN is delimited by
               bracketing quotes, the REPLACEMENT has its own
               pair of quotes, which may or may not be bracketing
               quotes, e.g., s(foo)(bar) or s<foo>/bar/.  A /e
               will cause the replacement portion to be
               interpreted as a full-fledged Perl expression and
               eval()ed right then and there.  It is, however,
               syntax checked at compile-time.

##</code><code>##

   ?PATTERN?
               This is just like the /pattern/ search, except
               that it matches only once between calls to the
               reset() operator.  This is a useful optimization
               when you want to see only the first occurrence of
               something in each file of a set of files, for
               instance.  Only ??  patterns local to the current
               package are reset.

[ ... snip ...]

       m/PATTERN/cgimosx

       /PATTERN/cgimosx

[ ... snip ...]

               If "/" is the delimiter then the initial m is
               optional.  With the m you can use any pair of non-
               alphanumeric, non-whitespace characters as
               delimiters. This is particularly useful for
               matching Unix path names that contain "/", to
               avoid LTS (leaning toothpick syndrome). If "?" is
               the delimiter, then the match-only-once rule of
               ?PATTERN? applies.  If "'" is the delimiter, no
               variable interpolation is performed on the
               PATTERN.