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.