expr match "$string" '.*\($substring\)'
从$string的结尾提取$substring, $substring是正则表达式.

expr "$string" : '.*\($substring\)'
从$string的结尾提取$substring, $substring是正则表达式.

1 stringZ=abcABC123ABCabc
2 # ======
3
4 echo `expr match "$stringZ" '.*\([A-C][A-C][A-C][a-c]*\)'` # ABCabc
5 echo `expr "$stringZ" : '.*\(......\)'` # ABCabc