-z is the second supported bash string comparison operator used to check if a string is empty or not. The -z operator functions similarly like -n operator. Below is an example: Most importantly, you should add spaces around the square brackets. If there are no spaces, bash will complain ...
str - the String to check, may be null Returns: true if the String is empty or null isNotEmpty public static boolean isNotEmpty(String str) Checks if a String is not empty ("") and not null. StringUtils.isNotEmpty(null) = false StringUtils.isNotEmpty("") = false StringUtils.isNotE...
Test if string has non whitespace characters in Bash, The backquotes execute the command within; bash line parsing convert tabs and newlines to blanks and joins double blanks. The echo command re-emits this string, which is shrunk to an empty string for the final test by [[ ]]. I think...
String comparison with test Command Here are some string comparison examples using the test command. Check if the string is not empty The-nflag checks if the string length is non-zero. It returns true if the string is non-empty, else it returns false if the string is empty: $ [ -n "...
Here is another option, “-n”, to check whether the specified string is empty or not. It works on the rule of checking the length of a string by counting the string characters in it. If the length of a particular string turns out to be other than zero, it will return “true”; ...
The variable is not empty. Here, we used the comparison operator represented with = to check whether the left and right sides of the specified expression in the if statement are equal. We compared the specified variable in both code snippets with an empty string (""). The if condition woul...
Here are two methods to check if an array is empty in bash. You check if array size is zero or you check if all the elements of the array form an empty string.
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...
匹配模板(类似正则表达式),据此查找要匹配的字符串 string 对满足pattern匹配条件的字符串进行替换的字符串 pattern 的格式参见 《Pattern-Matching》 https...://www.gnu.org/savannah-checkouts/gnu/bash/manual/bash.html#Pattern-Matching 使用示例: ## 替换所有数字为U $ str...# 如果只是要替换最后一个...
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。