33.1.3 Modifiers
After the optional word designator, you can add a sequence of one or more
of the following modifiers, each preceded by a `:'.
     
h- Remove a trailing pathname component, leaving only the head.
     
 t- Remove all leading pathname components, leaving the tail.
     
 r- Remove a trailing suffix of the form `.suffix', leaving
the basename.
     
 e- Remove all but the trailing suffix.
     
 p- Print the new command but do not execute it.
     
 s/old/new/- Substitute new for the first occurrence of old in the
event line.  Any delimiter may be used in place of `/'. 
The delimiter may be quoted in old and new
with a single backslash.  If `&' appears in new,
it is replaced by old.  A single backslash will quote
the `&'.  The final delimiter is optional if it is the last
character on the input line.
     
 &- Repeat the previous substitution.
     
 ga- Cause changes to be applied over the entire event line.  Used in
conjunction with `s', as in 
gs/old/new/,
or with `&'.
     
 G- Apply the following `s' modifier once to each word in the event.