Why you should not use the || and && operators instead of a Bash If Statement? Detailed Examples & FAQ How to check if a variable exists or is “null”? How to check if a file exists? How to check if a directory exists? How to check if a command succeeds or failed? How to do...
The Bash if statement is a fundamental construct that allows you to control the flow of your scripts based on specific conditions. By leveraging conditionals, such as numeric and string comparisons, and file and directory checks, you can create dynamic and responsive scripts. Additionally, nesting ...
问如何在bash脚本中使用if语句EN#前言：在生产工作中if条件语句是最常使用的，如使用来判断服务状态，...
if [ -e $file ]; then echo "File exists" else echo "File does not exists" fi 1. 2. 3. 4. 5. 6. 7. Similarly for example we can use while loop to check if file does not exists. This script will sleep until file does exists. Note bash negator "!" which negates the -e o...
Bash 中的 if..else 语句是这个样子的: if TEST-COMMAND then STATEMENTS1 else STATEMENTS2 fi 如果TEST-COMMAND 为真,那么 STATEMENT1 会被执行;而如果为假,那么 STATEMENT2 就会被执行。对于每一个 if 语句,只能有一个 else 语句与之对应。 让我们给上一个例子加一个 else 语句: #!/bin/bash echo -n...
== 等于,如:if [ "a"=="b" ],与=等价 注意:==的功能在[[]]和[]中的行为是不同的,如下: [[ a == z* ]] # 如果a以"z"开头(模式匹配)那么将为true [[ a == "z*" ]] # 如果a等于z*(字符匹配),那么结果为true [ a == z* ] # File globbing 和word splitting将会发生 [ "a" ...
Statement1 elif Expression2; then Statement2 else Statement3 fi 基础语法说明: if语句必须以单词fi终止。elif和else为可选项,表示其他条件 使用示例: 判断文件是否存在 #! /bin/bash if [ -f 123.txt ];then echo "file exists" else echo "file not exists" ...
脚本1:工作中如果要批量关机,可使用以下脚本查看192.168.4.0网段哪些是关机,哪些是开机状态。...#以user为用户名前缀 3.let i++ #每循环一次+1,也可写作i=i+1 4.批量删除把useradd换成userdel -r 脚本3.打印网卡配置文件的每一行...
if it exists. When an interactive shell that is not a login shell is started, bash reads and executes commands from /etc/bash.bashrc and ~/.bashrc, if these files exist. This may be inhibited by using the --norc option. The --rcfile file option will force bash to read and execute...
id user1 && echo 'user exists!' || useradd user1 如果用户不存在就添加,否则显示已经存在 !id user1&&useradd user1 ||echo 'user1 already exists!' 如果用户不存在,添加并给其与用户名同名的密码,否则显示其已经存在。 id user1 && echo 'user already exists!'|| useradd user1 && echo ‘user...