${parameter/pattern/string}
Pattern substitution. The pattern is expanded to produce a pattern just as in pathname expansion. Parameter is expanded and the longest match of pattern against its value is replaced with string. If pattern begins with /,all matches of pattern are replaced with string. Normally only the first match is replaced. If pattern begins with #,it must match at the beginning of the expanded value of parameter. If pattern begins with %,it must match at the end of the expanded value of parameter. If string is null,matches of pattern are deleted and the / following pattern may be omitted. If parameter is @ or *,the substitution 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 substitution operation is applied to each member of the array in turn,and the expansion is the resultant list.
