An example Analysis of the basis and principle of shell script

Editor to share with you the basis and principle of shell script example analysis, I believe that most people do not know much about it, so share this article for your reference, I hope you will learn a lot after reading this article, let's go to understand it!

1. Special variable

$#: view the number of variable parameters

$0: view the name of the script

$! : view the pid of shell backend

$@: view a list of all the parameters of the passing script

$*: view a list of all parameters, displayed as a single string

$: ID of the process of the script itself

$?: the result of the previous command shows that 0 succeeds and fails if it is not 0

two。 Internal environment variable $PATH SHELL current shellUID current user environment {0 | other numbers} = {root | other users} HOME current user directory PWD current directory HISTFILE history command path PS1 # [\ u@\ h\ W]\ $user @ hostname\ directory\ $3. Integer and character judgment 3.1 Integer judgment

-eq tests whether two integers are equal (equal)-ne tests whether two integers are equal (unequal)-gt tests whether a number is greater than a number (greater than)-lt tests whether a number is less than a number (less than)-ge tests a number greater than or equal to-le tests a number Less than or equal to 3.2character test = ~ Test whether it is matched by a regular expression-z "string" detects whether the character is empty Empty is true, not empty is false, for example: [- z ""] is true if vacuum is true-n "string" detects whether the character is not empty, if it is not empty, it is true, and if it is not empty, false characters are compared with [[]] Compare the first letter (a-zA-Z) in uppercase or lowercase; the higher the ascii value, the greater the uppercase and lowercase case A > a B > b but An is not greater than b [root@slave02 ~] # [["A")

< "B" ]][root@slave02 ~]# echo $?0[root@slave02 ~]# [[ "a" < "b" ]][root@slave02 ~]# echo $?04.文件判断-e：文件是否存在 -b：测试是否块设备文件-c：测试是否字符设备文件-f：测试是否普通文件-d：测试是否目录-h：测试是否符号链接文件-L：测试是否是符号链接文件-p：测试是否是命名管道文件-S：测试是否是套接字文件权限相关：-r 读-w 写-x 执行特殊权限-g-u-k等5.read输入选项：-p：指定提示符-t：指定提示等待的时间（秒）6.if判断多分支：if [ 条件 ];then statement1 .....elif [ 条件2 ];then statement2 ....else statement3 ....fi7.案例选择判断case $变量名 in 'value1') statement ... ;; 'value2') statement ... ;; *) statement .. ;; esac#case支持的通配符： * //任意长度任意字符 ? //任意单个字符 [] //指字范围内的任意单个字符 start|START //俩种选择8.for循环第一种：for ((expr1;expr2;expr3)) # expr1：初始值条件 #expr2：循环的范围进行退出 #expr3：变量的值使用{ 循环体}for ((expr1;expr2;expr3));do 循环体done第二种：for 变量 in 列表; do 循环体done9.while循环while循环用于不知道循环次数的场景，注意有退出条件while [ 条件 ];do statement .....done10.深入练习1.写一个脚本，输入三个数字进行相应的加减乘除[root@slave02 ~]# cat script01.sh #!/bin/basha=$1b=$2c=$3num1=$[$a+$b+$c]num2=$[$a-$b-$c]num3=$[$a*$b*$c]echo "$a + $b + $c" = $num1echo "$a - $b - $c" = $num2echo "$a * $b * $c" = $num3awk "BEGIN{printf \"$a/$b/$c=%.2f\n\",$a/$b/$c}"[root@slave02 ~]# source script01.sh 100 10 9100 + 10 + 9 = 119100 - 10 - 9 = 81100 * 10 * 9 = 9000100/10/9=1.112.猜数字游戏 规则：指定一个数字，只要猜到了这个数字则过关，否则显示数字大了或者数字小了 [root@master ~]# cat test03.sh #!/bin/bashnums=99read -p "please enter a number: " numif [ $num -gt $nums ];then echo "数字大了"elif [ $num -lt $nums ];then echo "数字小了"else echo "猜对"fi [root@master ~]# . test03.sh please enter a number: 10数字小了[root@master ~]# . test03.shplease enter a number: 100数字大了[root@master ~]# . test03.shplease enter a number: 99猜对3.写一个脚本，让nginx服务设置开机自启#$0是nginx本身 $1是变量对应着下面的start|stop|restart|status[root@192 init.d]# pwd/etc/init.d[root@192 init.d]# cat nginx #!/bin/bashcase $1 in 'start') /usr/local/nginx/sbin/nginx ;; 'stop') /usr/local/nginx/sbin/nginx -s stop ;; 'restart') /usr/local/nginx/sbin/nginx -s stop /usr/local/nginx/sbin/nginx ;; 'status') num=$(ps -ef |grep -v 'grep'|grep -c nginx:) if [ $num -eq 0 ];then echo "nginx is stoped" else echo "nginx is running" fi ;; *) echo "Usage: service $0 start|stop|restart|status" ;; esac #当判断有nginx进程数量则认为开启服务，否则认为服务开启失败4.利用for循环，创建user序号1-100的用户#创建用户user1-100[root@master ~]# cat test05.sh #!/bin/bashfor (( i=1;i/dev/null if [ $? -eq 0 ];then #只要判断用户成功，$?才会显示0，显示0则代表执行下一条命令，否则显示user以及存在 echo "success" else echo "user is exis" fidone5.利用while循环，计算1+2…100的值[root@slave02 ~]# cat which.sh #!/bin/bashs=0 #初始值0i=1 #判断的数值，最终到100停止while [ $i -le 100 ];dos=$[$s+$i] i=$[$i+1] #自增加数doneecho $s[root@slave02 ~]# source which.sh 5050 #随便输入一个数字进行计算的话，把100改为$1即可6.apache简单的一个编译部署脚本1.一般项目或者脚本，文件，放在相应的位置里，方便查找[root@slave02 tmp]# pwd/tmp[root@slave02 tmp]# lsapache[root@slave02 apache]# lsinstall_apache.sh soft[root@slave02 soft]# lsapr-1.7.0.tar.bz2 apr-util-1.6.1.tar.bz2 httpd-2.4.48.tar.bz2 httpd.service[root@slave02 apache]# cat install_apache.sh #!/bin/bash echo "欢迎使用此脚本" apachedir=/usr/local/apache if [ $UID -ne 0 ];then echo "伙计，请使用管理员身份运行"fiecho "正在安装依赖包..."yum -y install epel-release bzip2 "@Development Tools" &>

/ dev/nullyum-y install openssl-devel pcre-devel expat-devel libtool gcc gcc-c++ make & > / dev/nullid apache & > / dev/nullif [$?-ne 0] Then useradd-r-M-s / sbin/nologin apacheficd / tmp/apache/soft/tar-xf apr-1.7.0.tar.bz2tar-xf apr-util-1.6.1.tar.bz2tar-xf httpd-2.4.48.tar.bz2sed-I'/ $RM "$cfgfile" / d'apr-1.7.0/configureecho "is compiling and installing apr, please listen to the song to relax." Cd apr-1.7.0/ [!-d / usr/local/apr] if [$?-eq 0]; then. / configure-- prefix=/usr/local/apr & & make & & make install & > / dev/nullelse echo "apr has installed" ficd.. / apr-util-1.6.1/ [!-d / usr/local/apr-util] if [$?-eq 0] Then. / configure-- prefix=/usr/local/apr-util-- with-apr=/usr/local/apr & & make & & make install & / dev/nullelse echo "apr-util has installed" ficd.. / httpd-2.4.48/ [!-d / usr/local/apache/] if [$?-eq 0] Then./configure-- prefix=$apachedir\-- sysconfdir=/etc/httpd24\-- enable-so\-- enable-ssl\-- enable-cgi\-- enable-rewrite\-- with-zlib\-- with-pcre\-with-apr=/usr/local/apr\-- with-apr-util=/usr/local/apr-util/\ -- enable-modules=most\-- enable-mpms-shared=all\-- with-mpm=prefork make & & make install & > / dev/nullelse echo "httpd has been installed" ficd# is influential Ignore echo "export PATH=$apachedir/bin:\ $PATH" > / etc/profile.d/httpd.shln-s $apachedir/include/ / usr/include/apache & > / dev/nullgrep 'apache/man' / etc/man_db.conf & > / dev/nullif [$?-eq 1] Then sed-I "20aMANDATORY_MANPATH $apachedir/man" / etc/man_db.confelse echo "apache is help exists" fi [!-f / usr/lib/systemd/system/httpd.service] if [$?-eq 0] Then cp / clq/apache/soft/httpd.service / usr/lib/systemd/system/else echo "File already exists" fisystemctl daemon-reloadsystemctl enable-- now httpdnum02=$ (ps-ef | grep-v 'grep' | grep-c httpd) if [$num02-eq 0] Then echo "httpd Boot failed" else echo "httpd Boot success" fiecho "Welcome next time use [root@slave02 apache] # chmod + x install_apache.sh [root@slave02 apache] # source install_apache.sh [root@slave02 apache] # source install_apache.sh Welcome to use this script to install dependency packages. Apr is being compiled and installed, please listen to songs to relax. Apr and install apr-util and install httpd already installed apache is help exists already exists files skip httpd self-startup successfully welcome next time to use [root@slave02 ~] # systemctl status httpd.service ● httpd.service-Start http Loaded: loaded (/ usr/lib/systemd/system/httpd.service; enabled; vendor preset: disabled) Active: active (running) since Sat 2021-09-04 17:45:33 CST 5h 57min ago Main PID: 834761 (httpd) Tasks: 7 (limit: 5782) Memory: 6.3m CGroup: / system.slice/httpd.service ├─ 834761 / usr/local/apache/bin/httpd-k start ├─ 835358 / usr/local/apache/bin/httpd-k start ├─ 835359 / usr/local/apache/bin/httpd-k start ├─ 835360 / usr/local/apache/bin/httpd- K start ├─ 835361 / usr/local/apache/bin/httpd-k start ├─ 835362 / usr/local/apache/bin/httpd-k start └─ 836063 / usr/local/apache/bin/httpd-k start [root@slave02] # ss-antlState Recv-Q Send-Q Local Address:Port Peer Address:Port Process LISTEN 0 128 0.0.0.0 22 0.0.0.015 * LISTEN 0 128 *: 80 *: * LISTEN 0128 [:]: 22 [::]: * these are all the contents of the article "sample Analysis of the fundamentals and principles of shell scripts" Thank you for reading! I believe we all have a certain understanding, hope to share the content to help you, if you want to learn more knowledge, welcome to follow the industry information channel!