本文共 13320 字，大约阅读时间需要 44 分钟。
if语句语法 单分支结构语法： if [条件]; then 指令 fi 或 if [条件] then 指令 fi
[root@master4 day4]# cat if-single1.sh #!/bin/sh#功能：单分支if结构整数比较，用-lt格式例子#created by xsz#date:20180107if [ 10 -lt 12 ] then echo "Yes,10 is less than 12"fi[root@master4 day4]# sh if-single1.sh Yes,10 is less than 12传参方方式：[root@master4 day4]# cat if02.sh #/bin/shif [ $1 -lt $2 ] then echo "Year,$1 is less than $2"firead接收方式：[root@master4 day4]# cat if03.sh #/bin/shread -t 10 -p "please input two number:" num1 num2if [ $num1 -lt $num2 ] then echo "Year,$num1 is less than $num2"fi以上脚本问题1、无法完整比较整数大小2、没有对参数的个数以及变量内容做判断
范例三（请思考）：开发脚本实现如果/server/scripts下面存在if3.sh就输出到屏幕。
注意：如果执行脚本后发现该if3.sh不存在，就自动创建这个if3.sh脚本。我的脚本：#!/bin/bashi=/server/scripts/if3.sh[ -e $i ] && cat $i && exit 0if [ $(sh $i 2> /dev/null;echo $?) != 0 ] then echo "$i is no exist,touching if03.sh..." echo "I am if03.sh" > $ifi老男孩的脚本1：#!/bin/shdir=/server/scripts[ ! -d $dir ] && mkdir -p $dirfile="if3.sh"if [ -f "$dir/$file" ]; then echo "$file is exist." exit 0fitouch $dir/$file同学：[root@master4 day4]# cat tiaojian.sh #!/bin/shdir=/server/scriptsfile=if3.shcd $dir || mkdir -p $dir [ ! -f "$file" ] && touch $file || echo $file
开发脚本判断系统内存大小，如果低于100M就邮件报警。测试报警成功后加入系统定时任务每3分钟执行一次检查。常见发送邮件方法：[root@master4 day4]# mail -s "tittle" hanzhaodiba@163.com < /etc/hosts[root@master4 day4]# echo "oldboy" | mail -s "tittle" hanzhaodiba@163.com安装发邮件：yum install -y sendmailsendmail启动慢原因1、主机名没有配置好[root@master4 day4]# uname -nmaster4.com10.201.106.134 master4 master4.com[root@master4 day4]# netstat -tanp | grep 25 tcp 0 0 127.0.0.1:25 0.0.0.0:* LISTEN 15622/sendmail解答：重视解决问题的过程1、先再命令行把条件取出来（我的是CentOS7）[root@master4 day4]# free -m | grep Mem | awk '{print $NF}'1222、编写脚本[root@master4 day4]# vim if04.sh#!/bin/shcurrent_mem=`free -m | grep Mem | awk '{print $NF}'`mem_chars="our sys mem is:$current_mem"if [ $current_mem -lt 200 ];then echo "$mem_chars" | mail -s "tittle" 635254246@qq.comfi[root@master4 day4]# sh -x if04.sh ++ awk '{print $NF}'++ grep Mem++ free -m+ current_mem=178+ mem_chars='our sys mem is:178'+ '[' 178 -lt 200 ']'+ mail -s tittle 635254246@qq.com+ echo 'our sys mem is:178'加入到定时任务：[root@master4 day4]# crontab -l#monitor memory*/3 * * * * /bin/sh /server/scripts/day4/if04.sh > /dev/null 2>&1 我的脚本：[root@master4 day4]# cat if05.sh #!/bin/shif [ $1 -le $2 ];then if [ $1 -lt $2 ];then echo "$1 is less than $2" else echo "$1 is eq $2" fielse echo "$1 is big than $2"fi[root@master4 day4]# cat if-double01.sh #!/bin/shif [ $1 -lt $2 ];then echo "$1 < $2"else echo "$1 >= $2"fi[root@master4 day4]# sh if-double01.sh 4 54 < 5[root@master4 day4]# sh if-double01.sh 2 22 >= 2[root@master4 day4]# sh if-double01.sh 2 12 >= 1
[root@master4 day4]# cat if-double02.sh #!/bin/shread -p "please input first number:" num1read -p "please input second number:" num2if [ $num1 -lt $num2 ];then echo "$num1 < $num2"elif [ $num1 -gt $num2 ];then echo "$num1 > $num2"else echo "$num1 = $num2"fi[root@master4 day4]# sh if-double02.sh please input first number:4please input second number:34 > 3[root@master4 day4]# sh if-double02.sh please input first number:4please input second number:44 = 4[root@master4 day4]# sh if-double02.sh please input first number:4please input second number:54 < 5老男孩脚本1：[root@master4 day4]# cat if-multi01.sh #!/bin/shif [ $1 -lt $2 ];then echo "$1 < $2"elif [ $1 -eq $2 ];then echo "$1 = $2"else echo "$1 > $2"fi解决命令行传参，不加参数，报错问题：[root@master4 day4]# cat judge-if-multi01-argv.sh #!/bin/shif [ $# -ne 2 ];then echo "$0 Usage method: num1 num2" exit 1fiif [ $1 -lt $2 ];then echo "$1 < $2"elif [ $1 -eq $2 ];then echo "$1 = $2"else echo "$1 > $2"fi解决输入非整数的问题：过滤出数字：[root@master4 day4]# echo "3434dkjfkddfd99" | sed 's#[a-z]##g'343499反过来，过滤数字，看字段是否为0。把数字去掉，长度为0，说明是数字[root@master4 day4]# echo "3434dkjfkddfd99" | sed 's#[0-9]##g'dkjfkddfd[root@master4 day4]# cat judge-if-multi01-argv.sh #!/bin/shif [ $# -ne 2 ];then echo "$0 Usage method: num1 num2" exit 1fi[ -n "`echo $1|sed 's#[0-9]##g'`" ] && { echo "num1 must be int." exit}[ -n "`echo $2|sed 's#[0-9]##g'`" ] && { echo "num2 must be int." exit}if [ $1 -lt $2 ];then echo "$1 < $2"elif [ $1 -eq $2 ];then echo "$1 = $2"else echo "$1 > $2"fi测试：[root@master4 day4]# sh judge-if-multi01-argv.sh nu3 34v 343judge-if-multi01-argv.sh Usage method: num1 num2[root@master4 day4]# sh judge-if-multi01-argv.sh nu3 34vnum1 must be int.[root@master4 day4]# sh judge-if-multi01-argv.sh 43 34vnum2 must be int.[root@master4 day4]# sh judge-if-multi01-argv.sh 43 343 > 3[root@master4 day4]# sh judge-if-multi01-argv.sh 43 4343 = 43[root@master4 day4]# sh judge-if-multi01-argv.sh 43 5343 < 53 [ -n "`echo $num|sed 's/[0-9]//g'`" ] && echo "第二个参数必须为数字" && exit 1条件表达式，大括号的用法：[ -n "`echo $num|sed 's/[0-9]//'`" ] && { echo "第二个参数必须为数字" exit 1} [root@master4 day4]# num=521old521[root@master4 day4]# [ -z "`echo "${num//[0-9]/}"`" ] && echo 1 || echo 00[root@master4 day4]# 这个结果说明前面的结果不为1，字符串非空，即有非数字字符————————————————[root@master4 day4]# num=521[root@master4 day4]# [ -z "`echo "${num//[0-9]/}"`" ] && echo 1 || echo 01这个结果说明前面的结果去掉数字后为1，即没有非数字字符 思路：如果num长度不为0，并且把num中的非数字部分删除，然后看结果是不是等于num本身，如果两者都成立就是数字。[root@master4 day4]# num=123[root@master4 day4]# [ -n "$num" -a "$num" = "${num//[^0-9]/}" ] && echo "it is num"it is num[root@master4 day4]# num=1d3[root@master4 day4]# [ -n "$num" -a "$num" = "${num//[^0-9]/}" ] && echo "it is num" || echo "is not is num"is not is num[root@master4 day4]# 把变量和整数相加看是否成功执行：[root@master4 day4]# expr $1 + 0 > /dev/null 2>&1[root@master4 day4]# [ $? -eq 0 ] && echo int
我的脚本：#!/bin/shread -p "please input first num:" num1read -p "please input second num:" num2[ -n "`echo $num1|sed 's#[0-9]##g'`" ] && { echo "num1 must be int." exit}[ -n "`echo $num2|sed 's#[0-9]##g'`" ] && { echo "num2 must be int." exit}if [ $num1 -lt $num2 ];then echo "$num1 < $num2"elif [ $$num1 -eq $$num2 ];then echo "$num1 = $num2"else echo "$num1 > $num2"fi老男孩的脚本1：[root@master4 day4]# vim read03.sh#!/bin/shread -p "please input tow num:" a bexpr $a + 0 > /dev/null 2>&1RETVAL1=$?expr $b + 0 > /dev/null 2>&1RETVAL2=$?[ "$RETVAL1" -eq 0 -a $RETVAL2 -eq 0 ] || { echo "argv1 and argv2 must be int." exit 2}if (( $a<$b ));then echo "$a<$b"elif [ $a -eq $b ];then echo "$a=$b"else echo "$a>$b"fi 我的脚本1：[root@master4 MySQL]# cat 01.sh #!/bin/bash# pang duan mysqld startingif [ "`netstat -tan | grep 3306 | awk '{print $6}' | head -1`" == "LISTEN" ]; then echo "mysqld is starting"else echo "mysqld is stop.Now is starting mysqld service..." systemctl start mysqld.service pid=$(lsof -i:3306 | head -2 | grep mysqld | awk '{print $2}') echo "staring mysqld ok,the mysqld PID is $pid" fi我的脚本2：[root@master4 MySQL]# cat 02.sh #!/bin/bash# pang duan mysqld startingif [ "`systemctl status mysqld.service | grep Active | awk '{print $2}'`" == "active" ]; then echo "mysqld is starting"else echo "mysqld is stop.Now is starting mysqld service..." systemctl start mysqld.service pid=$(lsof -i:3306 | head -2 | grep mysqld | awk '{print $2}') echo "staring mysqld ok,the mysqld PID is $pid" fi[root@master4 MySQL]# 老男孩的脚本1（这个方法有问题，进程被杀死，取得值为空，会报错）：[root@master4 MySQL]# cat judgedb_by_port01.sh #!/bin/shport=`netstat -lnt | grep 3306 | awk -F '[ :]+' '{print $5}'`if [ $port -ne 3306 ];then echo "mysql is stoped" systemctl start mysqldfi老男孩的脚本1【改进版】（取netstat显示的行数）：[root@master4 MySQL]# cat judgedb_by_port01.sh #!/bin/shportnum=`netstat -lnt | grep 3306 | wc -l`if [ $portnum -ne 1 ];then echo "mysql is stoped" systemctl start mysqldelse echo "mysql is running"fi测试：[root@master4 MySQL]# sh judgedb_by_port01.sh mysql is stoped[root@master4 MySQL]# sh judgedb_by_port01.sh mysql is running[root@master4 MySQL]# 我的脚本1：[root@master4 MySQL]# cat judgedb_by_port01.sh #!/bin/shportnum=`netstat -lnt | grep 3306 | wc -l`pid=`ps -ed | grep mysqld | wc -l`if [ $portnum -ne 1 -o $pid -le 1 ];then echo "mysql is stoped" systemctl start mysqldelse echo "mysql is running"fi[root@master4 MySQL]# bash -x judgedb_by_port01.sh ++ wc -l++ netstat -lnt++ grep 3306+ portnum=0++ grep mysqld++ wc -l++ ps -ed+ pid=0+ '[' 0 -ne 1 -a 0 -le 1 ']'+ echo 'mysql is stoped'mysql is stoped+ systemctl start mysqld老男孩的脚本1：[root@master4 MySQL]# cat judgedb_by_port02.sh #!/bin/shportnum=`netstat -lnt | grep 3306 | wc -l`processsum=`ps -ef | grep mysql | grep -v grep | wc -l`if [[ $portnum -eq 1 || $processsum -eq 2 ]];then echo "mysql is running"else echo "mysql is stoped" echo "Staring MySQL..." systemctl start mysqldfi测试：[root@master4 MySQL]# sh -x judgedb_by_port02.sh ++ wc -l++ netstat -lnt++ grep 3306+ portnum=0++ grep -v grep++ wc -l++ ps -ef++ grep mysql+ processsum=0+ [[ 0 -eq 1 ]]+ [[ 0 -eq 2 ]]+ echo 'mysql is stoped'mysql is stoped+ systemctl start mysqld[root@master4 MySQL]# [root@master4 MySQL]# [root@master4 MySQL]# sh -x judgedb_by_port02.sh ++ wc -l++ netstat -lnt++ grep 3306+ portnum=1++ grep mysql++ grep -v grep++ ps -ef++ wc -l+ processsum=2+ [[ 1 -eq 1 ]]+ echo 'mysql is running'mysql is running[root@master4 MySQL]# 老男孩脚本2:[root@master4 MySQL]# cat judgedb_by_port03.sh #!/bin/bash#function:check mysql statusMySQLSTARTUP="systemctl start mysqld.service"DbProcessCount=`ps -ef | grep mysql | grep -v brep | wc -l`DbPortCount=`netstat -lnt | grep 3306 | wc -l`if [ $DbProcessCount -eq 2 ] && [ $DbPortCount -eq 1 ];then echo "MySQL is running"else $MySQLSTARTUP > /tmp/mysql.log sleep 10; DbProcessCount=`ps -ef | grep mysql | grep -v grep | wc -l` DbPortCount=`netstat -lnt | grep 3306 | wc -l` if [ $DbProcessCount -ne 2 ] || [ $DbPortCount -ne 1 ];then pkill mysqld > /dev/null 2>&1 sleep 5 pkill mysqld > /dev/null 2>&1 sleep 5 [ $DbProcessCount -eq 0 ] && MySQLSTARTUP >> /tmp/mysql.log [ $? -eq 0 ] && echo "mysql is started" fi mail -s "mysql restarted" xxxxxx@qq.com < /tmp/mysql.logfi
[root@master4 MySQL]# dos2unix judgedb_by_port03.sh dos2unix: converting file judgedb_by_port03.sh to Unix format ...
我的脚本1：[root@master4 MySQL]# cat 03.sh #!/bin/shvalue=`mysql -uroot -p'root' -S /var/lib/mysql/mysql.sock -e "SELECT VERSION();" > /dev/null 2>&1;echo $?`portnum=`netstat -lnt | grep 3306 | wc -l`processsum=`ps -ef | grep mysql | grep -v grep | wc -l`if [[ $portnum -eq 1 && $processsum -eq 2 && value -eq 0 ]];then echo "mysql is running"else echo "mysql is stoped" echo "Staring MySQL..." systemctl start mysqld Version=`mysql -uroot -p'root' -S /var/lib/mysql/mysql.sock -e "SELECT VERSION();" | grep -v "()"` echo "The MySQL version is $Version"fi老男孩的脚本1：[root@master4 MySQL]# cp judgedb_by_port02.sh judgedb_by_mysql04.sh[root@master4 MySQL]# cat judgedb_by_mysql04.sh#!/bin/shmysql -uroot -proot -S /var/lib/mysql/mysql.sock -e "SELECT VERSION();" >/dev/null 2>&1if [[ $? -eq 0 ]];then echo "mysql is running"else echo "mysql is stoped" echo "Staring MySQL..." systemctl start mysqldfi异地连接，使用-h IP
[root@master4 ~]# netstat -tan | grep 80tcp 0 0 0.0.0.0:80 0.0.0.0:* LISTEN tcp6 0 0 :::80 :::* LISTEN [root@master4 ~]# lsof -i :80[root@master4 ~]# ps -ef | grep nginx[root@node3 ~]# curl -I 10.201.106.134[root@node3 ~]# wget 10.201.106.134[root@node3 ~]# curl -o /dev/null -s -w "%{http_code}" 10.201.106.134 % Total % Received % Xferd Average Speed Time Time Time Current Dload Upload Total Spent Left Speed100 3700 100 3700 0 0 695k 0 --:--:-- --:--:-- --:--:-- 0curl -s 静默显示[root@node3 ~]# nmap 10.201.106.134 -p 80 | grep open | wc -l1[root@node3 ~]# curl -o /dev/null -s -w %{http_code} http://10.201.106.134200[root@node3 ~]# [root@node3 ~]# curl -s -I http://10.201.106.134 | sed -n '1p' | cut -d " " -f2200 [root@master4 nginx]# vim judgeweb_by_port01.sh #!/bin/shportnum=`nmap 10.201.106.134 -p 80 | grep open | wc -l`if [ $portnum -ne 1 ];then echo "nginx is stoped" systemctl start nginxelse echo "nginx is running"fi
[root@master4 nginx]# vim judgeweb_by_wget-url02.sh #!/bin/shwget -T 15 -q --spider http://10.201.106.134if [ $? -ne 0 ];then echo "nginx is stoped" systemctl start nginxelse echo "nginx is running"fi
[root@master4 nginx]# vim judgeweb_by_curl-code03.sh #!/bin/shhttpcode=`curl -o /dev/null -s -w %{http_code} http://10.201.106.134`if [ "$httpcode" != "200" ];then echo "nginx is stoped" systemctl start nginx else echo "nginx is running"fi[root@master4 nginx]# pkill nginx[root@master4 nginx]# sh judgeweb_by_curl-code03.sh nginx is stoped[root@master4 nginx]# sh judgeweb_by_curl-code03.sh nginx is running[root@master4 nginx]# 转载于:https://blog.51cto.com/zhongle21/2087365