1.Calculate the length of the variable

    [root@dong ~]# CHAR="I am dong"
    [root@dong ~]# echo $CHAR
    I am dong
    [root@dong ~]# echo ${#CHAR}
    9
    [root@dong ~]# echo $CHAR|wc -L
    9

2.Number of character from the second to the end(including spaces)

    [root@dong ~]# echo ${CHAR:2}
    am dong

3.Number of character from the second character to the N character(including spaces)
[root@dong ~]# echo ${CHAR:2:2}
am
[root@dong ~]# echo ${CHAR:2:4}
am d
[root@dong ~]# echo $CHAR|cut -c 3-9
am dong

4.匹配变量内容替换

    [root@dong ~]# CHAR="I am dong dong I am dong"
    [root@dong ~]# echo ${CHAR/dong/ling}
    I am ling dong I am dong
    Suffix Matching
    [root@dong ~]# echo ${CHAR/%dong/ling}
    I am dong dong I am ling
    [root@dong ~]# echo $CHAR
    abcABC123ABCabc
    [root@dong ~]# echo ${CHAR#a*C}
    123ABCabc
    [root@dong ~]# echo ${CHAR##a*C}
    abc
    [root@dong ~]# echo ${CHAR%%a*c}
[root@dong ~]# echo ${CHAR%a*c} 
abcABC123ABC</code></pre> 
<p>Because variable subtrings are rarely used,BAIDU can be used if necessary</p>