${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.