字符串处理

# 全局使用示例
v="I love you, Do you love me"

警告

expr 索引从1开始, $从0开始索引

变量替换

v="I love you, Do you love me"

语法	说明	例子	输出
${var#rule}	Delete the shortest from the beginning of variable	var=${v#*ov}	e you, Do you love me
${var##rule}	Delete the longest from the beginning of variable	var=${v##*ov}	e me
${var%rule}	Delete the shortest from the end of variable	var=${v%ov*}	I love you, Do you l
${var%%rule}	Delete the longest from the end of variable	var=${v%%ov*}	I l
${var/old/new}	Replace the first match	var=${v/love/hate}	I hate you, Do you love me
${var/old//new}	Replace the all match	var=${v//love/hate}	I hate you, Do you hate me

变量测试

字符串计算长度

	语法	说明	示例	输出
1	${#v}	the length, index start from 0	len=${#v}	26
2	`expr length "$v" `	If there are Spaces in the string, double quotation marks must be added, just used in Linux, macOS doesn't work, index start from 1	len=`expr length "$v"`	26

获取字符串位置

	语法	说明	示例	输出
1	`expr index $var substring`	获取第一个字符位置，拆分字符串为字符，然后匹配最先找到的字符，如例子中o是首先找到的, 索引从1开始	ind=`expr index "$v" you`	4
2	`expr match $var substring`	获取从头匹配的子串的长度, ind=`expr match "$v" you` 结果为0	ind=`expr match "$v" I.*`	26

抽取子串

	Syntax	Description	示例	输出
1	${var: postion}	start from the position, index start from 0	var=${v: 10}	, Do you love me
2	${var: postion: length}	start from position, the length of match is length	var=${v:10:6}	, Do y
3	${var: -postion}	From right side, there is a white-space between : and -	var=${v: -5}	ve me
4	${var: -postion:length}		var=${v: -5:4}	ve m
5	`expr substr "$var" position length`	start from position, the length of match is length with index from 1	str=`expr substr "$v" 10 6`	u, Do

练习：

string="Bigdata process framework is Hadoop, Hadoop is an open source project"


function print_tips
{
    echo "*********************************************"
    echo "(1) print the length of string"
    echo "(2) delete all Hadoop"
    echo "(3) replace the first Hadoop with Mapreduce"
    echo "(4) replace all the Hadoop with Mapreduce"
    echo "*********************************************"
}

function len_of_string() {
    echo "${#string}"
}

function del_hadoop() {
    echo "${string//Hadoop/}"
}

function rep_hadoop_mapreduce_first() {
    echo "${string/Hadoop/Mapreduce}"
}

function rep_hadoop_mapreduce_all() {
    echo "${string//Hadoop/Mapreduce}"
}


while true
 do
    echo "【 string=$string 】"
    echo
    print_tips
    read -p "Pls input your choice(1|2|3|4|Q|q):" choice

    case $choice in
          1)
            len_of_string
            ;;
          2)
            del_hadoop
            ;;
          3)
            rep_hadoop_mapreduce_first
            ;;
          4)
            rep_hadoop_mapreduce_all
            ;;
          q|Q)
            exit
            ;;
          *)
            echo "Error, input only in (1|2|3|4|Q|q)"
            ;;
    esac
done