test> var=http://www.aaa.com/123.htm
test> echo ${var#*//}
www.aaa.com/123.htm
test> echo ${var##*/}
123.htm
test> echo ${var%/*}
http://www.aaa.com
test> echo ${var%%/*}
http:
test> echo ${var:0:5}
http:
test> echo ${var:7}
www.aaa.com/123.htm
test> echo ${var:0-7:3}
123
test> echo ${var:0-7}
123.htm
# 去左边
%去右边
单一符号是最小匹配；两个符号是最大匹配
