nameref attribute)andvalueofany existing variablewiththe same name at a surrounding scope.Ifthereisno existing variable, the local variableisinitially unset. The following options can be usedtorestrict outputto
- Test if a given variable is [eq]ual/[n]ot [e]qual/[g]reater [t]han/[l]ess [t]han/[g]reater than or [e]qual/[l]ess than or [e]qual to the specified number: [[ $variable -eq|ne|gt|lt|ge|le integer ]] - Test if the specified variable has a [n]on-empty value: ...
- Test if a given variable is [eq]ual/[n]ot [e]qual/[g]reater [t]han/[l]ess [t]han/[g]reater than or [e]qual/[l]ess than or [e]qual to the specified number: [[ $variable -eq|ne|gt|lt|ge|le integer ]] - Test if the specified variable has a [n]on-empty value: ...
Variable ConditionalsExpressionValueWhat does it do? -o opt If shell option is enabled. -v var If variable has a value assigned. -R var If variable is a name reference. -z var If the length of string is zero. -n var If the length of string is non-zero....
forvariable_nameinvalue1 value2 value3 .. ndocommand1 command2 commandndone 现在让我们检查 bash for 循环的几个示例用法。 循环示例 在最简单的形式中,for 循环采用以下基本格式。在此示例中,变量 n 遍历一组用花括号括起来的数值,并将它们的值打印到标准输出。
forvariable_nameinvalue1 value2 value3..ndocommand1 command2 commandn done 现在让我们检查 bash for 循环的几个示例用法。 循环示例 在最简单的形式中,for 循环采用以下基本格式。在此示例中,变量 n 遍历一组用花括号括起来的数值,并将它们的值打印到标准输出。
if [[ ! -v var ]]; then echo "Variable is not set" elif [[ -z "$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...
通常shell将空格堪称命令行中单词的分隔符→if 要表示某参数包含空格(eg:包含空格的文件名),then 需要使用以下三种界定符使空格作为整体中的一部分 一对单引号:shell以字面意思看待内部的字符串,不加以解释 一对双引号:shell会解读里面的特殊字符 $ echo 'The variable HOME has value $HOME' ...
引用变量(Variable Substitution) Referencing (retrieving) its value is calledvariable substitution. Enclosing a referenced value indouble quotes(" ... ") does not interfere with variable substitution. This is calledpartial quoting, sometimes referred to as "weak quoting." Using single quotes (' .....
However, if the variable has the-iattribute set, the result is rounded to the closest integer. echo $testvarCopy Attempting to declare a non-integer value to a variable while the-ioption is set, results in an error. declare testvar="1.5"Copy ...