${#string}
返回$string的長度

${string:position}
在$string中，從$position位置之後開始提取子串

${string:position:length}
在$string中，從$position位置之後開始提取$length長度的子串

[root@localhost SHELL]# NAME="ni hao, ming tian"
[root@localhost SHELL]# echo $NAME
ni hao, ming tian
[root@localhost SHELL]# echo ${NAME}
ni hao, ming tian
[root@localhost
 
 SHELL]# echo ${#NAME}
17
[root@localhost SHELL]# echo ${NAME:3}
hao, ming tian
[root@localhost SHELL]# echo ${NAME:3:6}
hao, m
[root@localhost SHELL]# 

${string#substring}
從變數$string開頭開始刪除最短匹配$substring子串

${string##substring}
從變數$string開頭開始刪除最長匹配$sunstring子串

e
[root@localhost SHELL]# echo $NAME
 

abcABC123ABCabcde
[root@localhost SHELL]# echo ${NAME#a*C}
123ABCabcde
[root@localhost SHELL]# echo ${NAME##a*C}
abcde
[root@localhost SHELL]# 

${string%substring}
從變數$string結尾開始刪除最短匹配$substring子串

${string%%substring}
從變數$string結尾開始刪除最長匹配$substring子串

[root@localhost SHELL]# NAME=abcABC123ABCabc
 

[root@localhost SHELL]# echo $NAME
abcABC123ABCabc
[root@localhost SHELL]# echo ${NAME%%a*c}

[root@localhost SHELL]# echo ${NAME%a*c}
abcABC123ABC
[root@localhost SHELL]# echo ${NAME#b*c}
abcABC123ABCabc
[root@localhost SHELL]# echo ${NAME#bc}
abcABC123ABCabc
[root@localhost SHELL]# echo ${NAME%bc}
abcABC123ABCa
[root@localhost SHELL]# echo ${NAME%%bc}
abcABC123ABCa
[root@localhost SHELL]# echo ${NAME%C*c}
abcABC123AB
[root@localhost SHELL]# echo ${NAME%%C*c}
abcAB
[root@localhost SHELL]# echo ${NAME%%C*b}
abcABC123ABCabc
[root@localhost SHELL]# echo ${NAME}
abcABC123ABCabc
[root@localhost SHELL]# 

注意：在進行#或##匹配時，$string的首字元必須是被刪除子串$substring的第一個字元，不然無法匹配刪除；
在進行%或者%%匹配時，$string的最後一個字元必須是被刪除子串$substring的最後一個字元，不然無法進行刪除操作；

${parameter/parttern/string}
用string來替換第一個匹配的pattern

${parameter/#parttern/string}
從開頭匹配parameter變數中的pattern，匹配上後就用string來替換匹配的pattern

${parameter/%pattern/string}
從結尾開始匹配parameter變數中的pattern，匹配上後就用string替換匹配的pattern

${parameter//pattern/string}
用string來替換parameter變數中所有匹配的pattern

[root@localhost SHELL]# NAME="I am a student student"
[root@localhost SHELL]# echo ${NAME//student/teacher}
I am a teacher teacher
[root@localhost SHELL]# echo ${NAME/#student/teacher}
I am a student student
[root@localhost SHELL]# echo ${NAME/%student/teacher}
I am a student teacher
[root@localhost SHELL]# echo ${NAME/%I am /teacher}
I am a student student
[root@localhost SHELL]# echo ${NAME/#I am /teacher}
teachera student student
[root@localhost SHELL]# echo ${NAME/#I am a/teacher}
teacher student student
[root@localhost SHELL]# echo $NAME
I am a student student
[root@localhost SHELL]#