#!/bin/bash #: Description : print formatted sales report ## Build a long string of equals signs divider=== divider=$divider$divider ## Format strings for printf header="\n %-10s %11s %8s %10s\n" format=" %-10s %11.2f %8d %10.2f\n" ## Width of divider totalwidth=44 ## Pri...
You can assign data to a variable using the equals sign (=). The data you store in a variable can either be a string or a number. Let’s create a variable now on the command line: chapter_number=5 The variable name is on the left hand side of the equals sign, and the data whic...
如果if结构使用的不是test命令,而是普通命令,比如上一节的((...))算术运算,或者test命令与普通命令混用,那么可以使用 Bash 的命令控制操作符&&(AND)和||(OR),进行多个命令的逻辑运算。$ command1 && command2 $ command1 || command2对于&&操作符,先执行command1,只有command1执行成功后, 才会执行command2。
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 string comparison and check if a string equals to a value? How to check if a string is in an array?
In this example, the ‘until’ loop runs untilindexequals the length of thenumbersarray. Inside the loop, we print out a message with the current number, and then increment theindexby 1. Comparing the Different Loop Methods Each of these loop methods has its advantages and disadvantages. ‘Fo...
We’ll be checking whether 1 equals 2. If true, then the output will be “true”. 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 ...
defined. However, when a variable is defined but has no value, then the variable is “Not Set.” Similarly, when a variable is defined and has a value, then it is “Set.” Thus, declared variable but no value equals to “Not Set,” and declared variable with value equals to “Set....
There is three loop constructs available in bash: for-loop, while-loop, and until-loop. All the bash loop constructs have a return status equals to the exit status of the last command executed in the loop, or zero if no command was executed. The For loop...
If the current cursor position is at the end of the current command, the value of this variable equals ${#COMP_LINE}. This variable is available only in shell functions and external commands invoked by the programmable completion facilities (see the section "Programmable Completion" below). ...
2-1. 清除:清除/var/log下的log文件2-2. 清除:一个改良的清除脚本2-3. cleanup:一个增强的和广义的删除logfile的脚本3-1. 代码块和I/O重定向3-2. 将一个代码块的结果保存到文件3-3. 在后台运行一个循环3-4. 备份最后一天所有修改的文件.4-1. 变量赋值和替换...