Shell脚本是系统管理和自动化任务的利器。本文将带你从基础到高级，全面掌握Shell脚本编程的最佳实践。
Shell基础 第一个Shell脚本 #!/bin/bash # 这是一个注释 echo "Hello, World!" # 变量赋值和使用 name="World" echo "Hello, $name!" # 命令替换 current_date=$(date) echo "Today is: $current_date" # 反引号方式（不推荐） current_date=`date` echo "Today is: $current_date" Shebang说明：
#!/bin/bash：使用bash解释器 #!/bin/sh：使用sh解释器（更通用） #!/usr/bin/env bash：自动查找bash（更便携） 变量和数据类型 # 字符串变量 greeting="Hello" name="Alice" # 只读变量 readonly PI=3.14159 # 删除变量 unset name # 环境变量 export PATH=$PATH:/new/path # 字符串拼接 fullname="John $greeting" echo $fullname # 获取字符串长度 string="Hello, World" echo ${#string} # 13 # 字符串切片 echo ${string:0:5} # Hello echo ${string:7} # World # 默认值 echo ${name:-"Guest"} # 如果name未设置或为空，使用"Guest" # 数组 arr=(apple banana cherry) echo ${arr[0]} # apple echo ${arr[@]} # 所有元素 echo ${#arr[@]} # 数组长度 arr[3]="date" # 添加元素 unset arr[1] # 删除元素 控制结构 条件判断 # if语句 if [ "$name" == "Alice" ]; then echo "Welcome, Alice!" elif [ "$name" == "Bob" ]; then echo "Welcome, Bob!" else echo "Welcome, Guest!" fi # 数字比较 count=10 if [ $count -eq 10 ]; then echo "Count is 10" fi if [ $count -gt 5 ]; then echo "Count is greater than 5" fi if [ $count -lt 20 ]; then echo "Count is less than 20" fi # 字符串比较 if [ "$string1" == "$string2" ]; then echo "Strings are equal" fi if [ -n "$string" ]; then echo "String is not empty" fi # 文件测试 if [ -f "file.txt" ]; then echo "File exists and is a regular file" fi if [ -d "/tmp" ]; then echo "Directory exists" fi if [ -r "file.txt" ]; then echo "File is readable" fi if [ -w "file.txt" ]; then echo "File is writable" fi if [ -x "script.sh" ]; then echo "File is executable" fi # 逻辑运算 if [ $count -gt 5 ] && [ $count -lt 20 ]; then echo "Count is between 5 and 20" fi if [ $count -lt 5 ] || [ $count -gt 20 ]; then echo "Count is outside range 5-20" fi # 使用test命令 if test -f "file.txt"; then echo "File exists" fi # 双括号（更强大的算术比较） if (( count > 5 && count < 20 )); then echo "Count is between 5 and 20" fi 循环结构 # for循环 for i in 1 2 3 4 5; do echo $i done # 遍历文件 for file in *.txt; do echo "Processing: $file" done # C风格for循环 for ((i=0; i<10; i++)); do echo $i done # while循环 count=0 while [ $count -lt 5 ]; do echo $count count=$((count + 1)) done # 读取文件行 while IFS= read -r line; do echo "$line" done < file.txt # until循环 count=0 until [ $count -ge 5 ]; do echo $count count=$((count + 1)) done # break和continue for i in {1..10}; do if [ $i -eq 5 ]; then continue # 跳过5 fi if [ $i -eq 8 ]; then break # 在8处停止 fi echo $i done case语句 # 简单的case语句 read -p "Enter a color: " color case $color in red) echo "You chose red" ;; blue|green) echo "You chose blue or green" ;; *) echo "You chose something else" ;; esac # 复杂的case语句 case $1 in start) echo "Starting service..." ;; stop) echo "Stopping service..." ;; restart) echo "Restarting service..." ;; status) echo "Checking service status..." ;; *) echo "Usage: $0 {start|stop|restart|status}" exit 1 ;; esac 函数编程 定义和使用函数 # 定义函数 greet() { echo "Hello, $1!" } # 调用函数 greet "Alice" # 返回值 add() { local result=$(($1 + $2)) echo $result } sum=$(add 5 3) echo "Sum: $sum" # 返回状态码 check_file() { if [ -f "$1" ]; then return 0 # 成功 else return 1 # 失败 fi } if check_file "file.txt"; then echo "File exists" else echo "File does not exist" fi # 局部变量 global_var="I am global" my_function() { local local_var="I am local" echo "Inside function: $local_var" echo "Inside function: $global_var" } my_function echo "Outside function: $global_var" # echo "Outside function: $local_var" # 错误：local_var未定义 函数参数 # 处理多个参数 process_args() { echo "First argument: $1" echo "Second argument: $2" echo "All arguments: $@" echo "Number of arguments: $#" echo "Script name: $0" } process_args arg1 arg2 arg3 # 遍历所有参数 iterate_args() { for arg in "$@"; do echo "Processing: $arg" done } iterate_args file1.txt file2.txt file3.txt # shift命令 shift_test() { echo "Total arguments: $#" echo "First: $1" shift echo "After shift, first: $1" echo "Remaining arguments: $#" } shift_test a b c d 递归函数 # 阶乘（尾递归） factorial() { local n=$1 local acc=${2:-1} if [ $n -le 1 ]; then echo $acc else factorial $((n - 1)) $((acc * n)) fi } echo "Factorial of 5: $(factorial 5)" # Fibonacci fibonacci() { local n=$1 if [ $n -le 1 ]; then echo $n else echo $(( $(fibonacci $((n - 1))) + $(fibonacci $((n - 2))) )) fi } echo "Fibonacci of 10: $(fibonacci 10)" 输入输出 读取用户输入 # 简单输入 read -p "Enter your name: " name echo "Hello, $name!" # 密码输入（不显示） read -s -p "Enter password: " password echo # 带超时的输入 read -t 5 -p "Enter your choice (5 seconds): " choice echo "You chose: $choice" # 读取多个值 read -p "Enter name age: " name age echo "Name: $name, Age: $age" # 从文件读取 while IFS= read -r line; do echo "Line: $line" done < input.txt # 读取确认 read -p "Continue? (y/n): " confirm if [[ $confirm == [yY] ]]; then echo "Continuing..." else echo "Aborting..." exit 1 fi 输出格式化 # echo选项 echo -n "No newline" # 不换行 echo -e "Line1\nLine2" # 解释转义字符 echo "Hello\tWorld" # 需要配合-e # printf格式化输出 printf "Name: %s, Age: %d\n" "Alice" 25 printf "Pi: %.2f\n" 3.14159 printf "%-10s %10s\n" "Left" "Right" # 重定向输出 echo "Error message" >&2 # 输出到stderr echo "Log message" >> logfile # 追加到文件 # 管道 echo "Hello World" | tr '[:upper:]' '[:lower:]' # Here文档 cat << EOF This is a multi-line string using Here document. EOF # Here字符串 grep "pattern" <<< "This is a string to search" 命令行参数 处理位置参数 #!/bin/bash # script.sh echo "Script name: $0" echo "First argument: $1" echo "Second argument: $2" echo "All arguments: $@" echo "Number of arguments: $#" # 检查参数数量 if [ $# -lt 2 ]; then echo "Usage: $0 <arg1> <arg2>" exit 1 fi 使用getopts #!/bin/bash # 使用getopts处理选项 usage() { echo "Usage: $0 [-a] [-b VALUE] [-c] filename" exit 1 } while getopts ":ab:c" opt; do case $opt in a) echo "Option -a triggered" ;; b) echo "Option -b triggered with value: $OPTARG" value=$OPTARG ;; c) echo "Option -c triggered" ;; \?) echo "Invalid option: -$OPTARG" usage ;; :) echo "Option -$OPTARG requires an argument" usage ;; esac done shift $((OPTIND-1)) echo "Remaining arguments: $@" 使用getopt（更强大） #!/bin/bash # 使用getopt处理长选项 TEMP=$(getopt -o ab:c:: --long alpha,bravo:,charlie:: -n 'example.sh' -- "$@") if [ $? != 0 ]; then echo "Terminating..." >&2 exit 1 fi eval set -- "$TEMP" while true; do case "$1" in -a|--alpha) echo "Option a" shift ;; -b|--bravo) echo "Option b, argument '$2'" shift 2 ;; -c|--charlie) case "$2" in "") echo "Option c, no argument" shift 2 ;; *) echo "Option c, argument '$2'" shift 2 ;; esac ;; --) shift break ;; *) echo "Internal error!" exit 1 ;; esac done echo "Remaining arguments:" for arg in "$@"; do echo " --> '$arg'" done 信号处理 捕获中断 #!/bin/bash # 捕获Ctrl+C cleanup() { echo "Cleaning up..." # 删除临时文件等 rm -f /tmp/my_script_temp* exit 1 } trap cleanup SIGINT SIGTERM echo "Press Ctrl+C to interrupt..." for i in {1..100}; do echo "Working... $i" sleep 1 done 捕获EXIT信号 #!/bin/bash # 确保清理代码总是执行 cleanup() { echo "Script is exiting..." rm -f /tmp/tempfile } trap cleanup EXIT # 创建临时文件 touch /tmp/tempfile echo "Doing some work..." # 即使脚本出错，cleanup也会执行 文本处理 文件操作 # 读取文件 while IFS= read -r line; do echo "$line" done < file.txt # 写入文件 echo "Hello" > output.txt echo "World" >> output.txt # 检查文件是否存在 if [ -f "file.txt" ]; then echo "File exists" fi # 检查文件是否可读 if [ -r "file.txt" ]; then echo "File is readable" fi # 获取文件大小 size=$(wc -c < file.txt) echo "File size: $size bytes" # 获取行数 lines=$(wc -l < file.txt) echo "File lines: $lines" 文本转换 # 转换为大写 echo "hello" | tr '[:lower:]' '[:upper:]' # 删除重复行 sort file.txt | uniq # 只显示重复行 sort file.txt | uniq -d # 统计重复次数 sort file.txt | uniq -c # 替换文本 sed 's/old/new/g' file.txt # 删除空行 sed '/^$/d' file.txt # 提取特定列 awk '{print $1, $3}' file.txt # 按模式分割文件 awk '/pattern/{filename="part_"++count".txt"; print > filename}' 进程管理 后台执行 # 后台运行 command & # 后台运行并重定向输出 command > /dev/null 2>&1 & # 使用nohup（退出终端后继续运行） nohup command & # 查看后台任务 jobs # 带回后台任务 fg %1 # 继续后台任务 bg %1 # 杀死后台任务 kill %1 进程监控 # 查看进程 ps aux # 查找特定进程 ps aux | grep nginx # 实时监控 top # 杀死进程 kill PID kill -9 PID # 强制杀死 # 等待进程完成 wait PID 调试技巧 调试模式 #!/bin/bash # 启用调试模式 set -x # 在执行前打印命令 set -v # 打印输入行 # 或者 bash -x script.sh # 只调试部分代码 set -x # 开始调试 # 需要调试的代码 set +x # 结束调试 错误处理 #!/bin/bash # 遇到错误立即退出 set -e # 使用未定义变量时报错 set -u # 管道命令失败时退出 set -o pipefail # 组合使用 set -euo pipefail # 捕获错误 trap 'echo "Error on line $LINENO"; exit 1' ERR 日志记录 #!/bin/bash # 日志函数 log() { local level=$1 shift echo "[$(date '+%Y-%m-%d %H:%M:%S')] [$level] $@" | tee -a script.log } log INFO "Script started" log ERROR "An error occurred" log WARNING "This is a warning" 实用示例 系统监控脚本 #!/bin/bash # 系统监控脚本 while true; do clear echo "=== System Monitor ===" echo "Time: $(date)" echo # CPU使用率 echo "CPU Usage:" top -bn1 | grep "Cpu(s)" | sed "s/.*, *\([0-9.]*\)%* id.*/\1/" | awk '{print 100 - $1"%"}' # 内存使用 echo -e "\nMemory Usage:" free -h # 磁盘使用 echo -e "\nDisk Usage:" df -h sleep 5 done 日志分析脚本 #!/bin/bash # Apache日志分析 log_file="/var/log/apache2/access.log" echo "=== Top 10 IPs ===" awk '{print $1}' "$log_file" | sort | uniq -c | sort -rn | head echo -e "\n=== Top 10 URLs ===" awk '{print $7}' "$log_file" | sort | uniq -c | sort -rn | head echo -e "\n=== HTTP Status Codes ===" awk '{print $9}' "$log_file" | sort | uniq -c | sort -rn 自动备份脚本 #!/bin/bash # 自动备份脚本 SOURCE_DIR="/path/to/source" BACKUP_DIR="/path/to/backup" DATE=$(date +%Y%m%d_%H%M%S) BACKUP_NAME="backup_$DATE.tar.gz" # 创建备份 echo "Creating backup..." tar -czf "$BACKUP_DIR/$BACKUP_NAME" "$SOURCE_DIR" # 删除30天前的备份 find "$BACKUP_DIR" -name "backup_*.tar.gz" -mtime +30 -delete echo "Backup completed: $BACKUP_NAME" 最佳实践 代码风格 使用Shebang：始终在脚本开头指定解释器 添加注释：解释复杂逻辑和重要步骤 使用有意义的变量名：避免单字母变量（除循环变量外） 缩进代码：使用一致的缩进（通常是4个空格） 引用变量：始终使用引号包裹变量（"$var"而非$var） 安全建议 验证输入：始终验证用户输入和参数 使用绝对路径：避免路径混淆 最小权限原则：只授予必要的权限 清理临时文件：脚本结束时清理 避免eval：除非绝对必要，否则不使用eval 性能优化 避免外部命令：尽量使用内置功能 减少子shell：避免不必要的进程创建 使用管道：而不是临时文件 批量处理：一次处理多个项目 缓存结果：避免重复计算 小结 Shell脚本是系统管理和自动化的强大工具。通过本文，你学习了：
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