Shell编程系列 https://www.jianshu.com/nb/37140890

计算字符串长度

• ${#string}
• expr length "$string"

v1="i love you"
len=`expr length "$v1"`
echo len

获取子串中字符在字符串中的位置

• expr index "subString"

v1="i love you"
v2="ou"
subIndex=`expr index "${v1}" "${v2}"`
echo $subIndex
# 4

# 注意： 他其实是找子串中每个字符的其实位置，返回最前面的那个

获取子串从头开始匹配的长度

• expr match "substr"

v1="i love you"
v2="ou"
v3="i love"
v4="i losadf"
v5="i lov.*"
subLen1=`expr match "$v1" "$v2"`
subLen2=`expr match "$v1" "$v3"`
subLen3=`expr match "$v1" "$v4"`
subLen4=`expr match "$v1" "$v5"`
echo $subLen1 $subLen2 $subLen3 $subLen4
# 0 6 0 10

抽取子串

# 0123456789
# iloveyou.
v1="iloveyou."
# 从第零位开=始
echo ${v1:0}
# iloveyou.

# 从第三位开始
echo ${v1:3}
# veyou.

# 从右边开始匹配 倒数第三个开始 注意冒号后面有空格 从右边-1开始数
echo ${v1: -3}
# ou.

echo ${v1: -3:1}
# o

# 从左边开始匹配  
echo ${v1:(-3)}
# ou.

# 从第2位开始 截取3个
expr substr "$v1" 2 3
# lov

# 注意expr 索引从1开始 ${}是从0开始

练习题

给定一个字符串变量
string=“You are an ugly boy! I'm a handsome boy!”
要求启动脚本后
1.输入1 打印字符串长度
2.输入2 删除ugly 把 an 变成 a
3.输入3 替换 'm 为 “ am” .
4.输入4 替换 ! 为 .

#!/bin/bash

string="You are an ugly boy! I'm a handsome boy!"

function print_tips
{
    echo "********************************"
    echo "1.输入1 打印字符串长度."
    echo "2.输入2 删除ugly 把 an 变成 a"
    echo "3.输入3 替换 'm 为 “ am” ."
    echo "4.输入4 替换 ! 为 ."
    echo "********************************"
}
function len_of_string
{
    echo "${#string}"
}

function del_ugly_and_change_an_to_a
{
    str="${string/ ugly/}"
    echo "${str/an/a}"
}

function replace_m_am
{
    echo "${string//\'m/ am}"
}

function replace_exclamation_mark_to_dot
{
    echo "${string//!/.}"
}

while true
do
    echo "「string = ${string} 」"
    echo
    print_tips
    read -p "Please input your choice (1|2|3|4|q)" choice

    case $choice in
        1)
            len_of_string
            ;;
        2)
            del_ugly_and_change_an_to_a
            ;;
        3)
            replace_m_am
            ;;
        4)
            replace_exclamation_mark_to_dot
            ;;
        q|Q
            exit
            ;;
        *)
            echo "Error, Input only in (1|2|3|4|q)"
            ;;
    esac
done