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