if [ -z "$var" ]; then echo "var is unset"; else echo "var is set to '$var'"; fi This is because it doesn't distinguish between a variable that is unset and a variable that is set to the empty string. That is to say, ifvar='', then the above solution will incorrectly ou...
if [ -z ${var+x} ]; then echo "var is unset"; else echo "var is set to '$var'"; fi 参考:https://stackoverflow.com/questions/3601515/how-to-check-if-a-variable-is-set-in-bash 6、换算秒为分钟、小时 代码语言:javascript 复制 #!/bin/bash a=60100 swap_seconds () { SEC=$1...
Using if Statement We can use an if statement with different variations to determine whether the provided Boolean variable is true. Note that the examples covered in this section will be similar. We will learn the first example in Use if with true Condition in detail, but later, we will dis...
Create a bash file named “check_var2.sh” and add the following script. Here, a string value is assigned to the variable, $str before checking the variable is set or unset. The ‘if’ condition will return true and the message, “’str’ variable is set and the value is Hello” wi...
Bash has a few conditional expressions, of which you can use one to check if a variable is empty or not. That is the-zoperator. Using the-zoperator followed by a variable will result in trueif the variable is empty. The condition will evaluate to false if the variable is not empty. ...
Why is printf better than echo? How to check if a variable is set in Bash? SettingIFSfor a single statement readarray(akamapfile) issue Tools Match command-line arguments to their help text Bash/Tcsh Comparison Table Collections of scripts ...
# Set the variable variable="" # Check if the variable is empty if [ -z "$variable" ]; then echo "Variable is empty." else echo "Variable is not empty." fi Copy Save changes and exit from the nanotext editor. Finally, use the chmod command to make the file executableas shown: ...
There are multiple ways to check if a variable is empty or not. Before moving towards those methods, knowing when a variable is called empty is necessary. In
bash shell参数展开(Shell Parameter Expansion):替换变量(variable)中的字符串 在写bash shell脚本时,如果遇到要替换变量中的字符串,首先想到的就是用sed命令,比如下面的示例将变量str中的数字123替换成UUU: $ str=hello,word,123 $ echo...,按照{parameter/pattern/string}的模式可以简单的如下替换 {parameter...
Check file types and compare values. Returns 0 if the condition evaluates to true, 1 if it evaluates to false. More information: https://www.gnu.org/software/bash/manual/bash.html#index-_005b_005b. - Test if a given variable is equal/not equal to the specified string: ...