后端

# 定义变量
name="John"
age=25

# 使用变量
echo "Name: $name"
echo "Age: $age"

# 使用花括号避免变量名混淆
echo "${name}_doe"

# 字符串长度
str="Hello"
echo "Length: ${#str}"

# 字符串截取
echo "${str:1:3}"  # 输出 "ell"

# 字符串替换（仅替换第一个匹配）
echo "${str/el/XX}"  # 输出 "HXXlo"

# 字符串替换（替换所有匹配）
echo "${str//l/XX}"  # 输出 "HeXXXXo"

# 字符串删除（从开头删除最短匹配）
path="/home/user/file.txt"
echo "${path#*/}"  # 输出 "home/user/file.txt"

# 字符串删除（从开头删除最长匹配）
echo "${path##*/}"  # 输出 "file.txt"

# 字符串删除（从结尾删除最短匹配）
echo "${path%/*}"  # 输出 "/home/user"

# 字符串删除（从结尾删除最长匹配）
echo "${path%%/*}"  # 输出 ""

# 命令替换
current_date=$(date)
echo "Current date: $current_date"

# 算术运算
num1=10
num2=5
sum=$((num1 + num2))
echo "Sum: $sum"

# 条件赋值
unset var
default_value="default"
echo "${var:-$default_value}"  # 输出 "default"

# 读取用户输入
read -p "Enter your name: " username
echo "Hello, $username!"

#!/bin/bash

# 脚本名称：shell_basics.sh
# 功能：演示Shell脚本基本操作和变量使用

# 定义变量
script_name="$0"
arg_count="$#"

# 输出脚本信息
echo "Script name: $script_name"
echo "Number of arguments: $arg_count"
echo "Arguments: $@"

# 检查参数
if [ $arg_count -eq 0 ]; then
    echo "No arguments provided"
elif [ $arg_count -eq 1 ]; then
    echo "One argument provided: $1"
else
    echo "Multiple arguments provided"
fi

# 算术运算
a=10
b=5
sum=$((a + b))
difference=$((a - b))
product=$((a * b))
quotient=$((a / b))

echo "Arithmetic operations:"
echo "$a + $b = $sum"
echo "$a - $b = $difference"
echo "$a * $b = $product"
echo "$a / $b = $quotient"

# 字符串操作
greeting="Hello, World!"
echo "Original string: $greeting"
echo "Length: ${#greeting}"
echo "Substring: ${greeting:7:5}"  # 从第7个字符开始，取5个字符
echo "Replaced: ${greeting/World/Shell}"

# 命令替换
echo "Current directory: $(pwd)"
echo "Current date: $(date)"
echo "Number of files: $(ls -l | wc -l)"

# 输出退出状态码
echo "Script completed with exit code: $?"