UNIX for Dummies Questions & Answers

       ${parameter#word}
       ${parameter##word}
              The  word  is  expanded to produce a pattern just as in pathname expansion.  If the
              pattern matches the beginning of the value of parameter, then  the  result  of  the
              expansion  is  the  expanded  value of parameter with the shortest matching pattern
              (the ‘‘#’’ case) or the longest matching pattern (the  ‘‘##’’  case)  deleted.   If
              parameter  is  @  or *, the pattern removal operation is applied to each positional
              parameter in turn, and the expansion is the resultant list.   If  parameter  is  an
              array variable subscripted with @ or *, the pattern removal operation is applied to
              each member of the array in turn, and the expansion is the resultant list.

       ${parameter%word}
       ${parameter%%word}
              The word is expanded to produce a pattern just as in pathname  expansion.   If  the
              pattern  matches  a  trailing  portion of the expanded value of parameter, then the
              result of the expansion is the expanded value of parameter with the shortest match‐
              ing  pattern  (the  ‘‘%’’  case)  or the longest matching pattern (the ‘‘%%’’ case)
              deleted.  If parameter is @ or *, the pattern removal operation is applied to  each
              positional  parameter in turn, and the expansion is the resultant list.  If parame‐
              ter is an array variable subscripted with @ or *, the pattern removal operation  is
              applied  to  each  member  of the array in turn, and the expansion is the resultant
              list.