str - the String to check, may be null Returns: true if the String is not empty and not null 判断是否null、空串或空白串 是null或空串或空白串:方法一 if (s == null || s.length() == 0 || s.trim().length() == 0) { // do something } 是null或空串或空白串:方法二 if (s ...
Example 3: Check if string is null or empty in Bash Unlike some other languages like C++, in Bash you can check whether the string is null or empty with one single command: if [ -z "$VAR" ] The -z actually checks if length of the variable is zero or not. If the variable is no...
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?
-n is one of the supported bash string comparison operators used for checking null strings in a bash script. When -n operator is used, it returns true for every case, but that’s if the string contains characters. On the other hand, if the string is empty, it won’t return true. -...
检测bash脚本中的程序错误可以使用以下方法: 1. 使用shellcheck工具。shellcheck是一个静态分析工具,可以检测bash脚本中的常见错误,例如语法错误、不安全的用法、可疑的用法等...
Here, we list some basic bash syntax with a brief explanation. It is a good starting point if you are a beginner.
In this example, the substitution command is used with $() to capture the output of grep, and then the -z option of the test command is used to check if the resulting string is empty or not. Here, the grep command searches for the pattern pattern in the file dummy.txt. The output...
有一个很好的机会，你的起始str实际上应该被填充为一个数组而不是一个字符串，但是如果你的值都不能...
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It can also be used to check if a command exists. For example, the above code is similar to the previous two but uses the type -p command to check if the grep command exists. Again, we used the > operator to redirect the command’s output to the null device, which discards the ...