- Testifthe specified variable has a [n]on-empty value: [[ -n$variable]] - Testifthe specified variable has an empty value: [[ -z$variable]] - Testifthe specified [f]ile exists: [[ -f path/to/file ]] - Testifthe specified [d]irectory exists: [[ -d path/to/directory ]] ...
echo "Variable is not set" elif [[ -z "$var" ]]; then echo "Variable is set to the empty string" else echo "Variable has the value: $var" fi OUTPUT 1 2 3 Variable has the value: /root Use the if-else statement with the -n option to check if the environment variable is ...
ShellCheck will warn when using features not supported by the shebang. For example, if you set the shebang to#!/bin/sh, ShellCheck will warn about portability issues similar tocheckbashisms: echo{1..$n}# Works in ksh, but not bash/dash/shecho{1..10}# Works in ksh and bash, but ...
(4) ${var:?message}, ${var?message}: 如果为空或未被设置,则显示错误信息到标准错误输出 $ ./checkarg ./checkarg: line2:1: An argument is required $ ./checkarg x ./checkarg: line2:2: Two arguments are required $ ./checkarg'''./checkarg: line5:1: A non-empty argument is requ...
forvariable_nameinvalue1 value2 value3..ndocommand1 command2 commandn done 现在让我们检查 bash for 循环的几个示例用法。 循环示例 在最简单的形式中,for 循环采用以下基本格式。在此示例中,变量 n 遍历一组用花括号括起来的数值,并将它们的值打印到标准输出。
從 shell 的角度來看,一個變數 variable 是一個由名稱 name 代表的引數。一個 變數有一個值 value 以及零個或多個屬性 attibutes。屬性可以使用內建命令 declare 來設定(參見下面 shell 內建 命令(SHELL BUILTIN COMMANDS) 章節中對 declare 的描述)。 如果給一個引數賦值,那麼它就被定義了。空字串是有效...
In this example, we’ve created an array namedfruitswith three elements: ‘apple’, ‘banana’, and ‘cherry’. The ‘for’ loop then iterates over each element in the array. For each iteration, the current element’s value is stored in thefruitvariable, which we then use in theechocom...
/bin/bash # 方法一:直接赋值 array1=("value1" "value2" "value3") # 方法二:使用索引赋值 array2[0]="value1" array2[1]="value2" array2[2]="value3" # 方法三:从字符串分割赋值 string="value4 value5 value6" array3=($string) # 方法四:使用read命令赋值 echo "Enter values separated...
I can embed the if-condition in the loop itself, but that would only be useful to check if a value is present, not if a value is absent. That is why I use the flag variable. I do this first, by looping over every element of the array. Then, by using the==operator to check if...
#Check the variable is set or not after assigning the value if[-z${Num}];then echo"’Num’ variable is not set" else echo"’Num is set and the value of Num=$Num" fi Run the script. $bashcheckvar1.sh Example-2: Check the variable is set or unset using parameter substitute ...