除了分号,Bash 还提供两个命令组合符&&和||,允许更好地控制多个命令之间的继发关系。 Command1 && Command2 上面命令的意思是,如果Command1命令运行成功,则继续运行Command2命令。 Command1 || Command2 上面命令的意思是,如果Command1命令运行失败,则继续运行Command2命令。 下面是一些例子。 $ cat filelist.txt ...
Bash Select Command, Fahmida Yesmin 14.Bash 函数本章介绍 Bash 函数的用法。简介函数(function)是可以重复使用的代码片段,有利于代码的复用。它与别名(alias)的区别是,别名只适合封装简单的单个命令,函数则可以封装复杂的多行命令。函数总是在当前 Shell 执行,这是跟脚本的一个重大区别,Bash 会新建一个子 ...
In this example we declare simple bash variable and print it on the screen ( stdout ) with echo command. #!/bin/bash STRING="HELLO WORLD!!!" echo $STRING 1. 2. 3. Your backup script and variables: #!/bin/bash OF=myhome_directory_$(date +%Y%m%d).tar.gz tar -czf $OF /home/l...
Occasionally you might want to run a command like you would on the command line and store the result of that command in a variable. We can do this by wrapping the command in a dollar sign and parentheses ($( )) around a command. This syntax is calledcommand substitution. The command is...
# Create the variable name. $ var="world" $ ref="hello_$var" # Print the value of the variable name stored in 'hello_$var'. $ printf '%s\n' "${!ref}" value 1. 2. 3. 4. 5. 6. 7. 8. 9. 或者,在bash4.3+上:
The break command syntax is break [n] and can be used in any bash loop construct. The [n] parameter is optional and allows you to specify which level of enclosing loop to exit, the default value is 1. The return status is zero, unless n is not greater or equal to 1. [me@linux ...
In this example, the ‘while’ loop continues to echo the count as long as the count is less than or equal to 5. The((count++))command increments the count after each iteration. The ‘Until’ Loop The ‘until’ loop is similar to the ‘while’ loop, but it performs a set of comm...
11. Declare Command 在Terminal中输入 展示shell内的所有变量 declear -p 定义自己的变量 declear myvariable declear myvariable=22 declear myvariable=11 声明限制变量 #! /bin/bash declear -r pwdfile=/etc/passswd echo $pwdfile pwdfile=/etc/abc.txt echo $pwdfile ...
Otherwise, the output will be “false”. $ test 1 -eq 2 && echo“true” || echo“false” Let’s break it down. test: The test command. 1: The first element for comparison. -eq: Comparison method (whether values are equal). 2: The second element for comparison. If the test ...
This is an alternative to sed, awk, perl and other tools. The function below works by finding all leading and trailing white-space and removing it from the start and end of the string. The : built-in is used in place of a temporary variable....