-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 ...
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”; o...
Afterdeclaring a string variable, use the-zoperator in anif statementto check whether a string is empty or not: MY_STRING="" if [ -z $MYSTRING ] then echo "String is empty" else echo "String is not empty" fi For more Shell scripting tips,check out or Bash/Shell scripting articles!
ls #文件列表wc –l filewc -w filewc -c sourcefile #计算文件行数计算文件中的单词数计算文件中的字符数cp sourcefile destfile #文件拷贝mv oldname newname #重命名文件或移动文件rm file #删除文件grep'pattern'sourcefile #在文件内搜索字符串比如:grep'se...
# Check if the string is empty if [ -z "$input_str" ]; then echo "The string is empty" else echo "The string is not empty" fi Output: The string is empty Explanation: In the exercise above, The variable 'input_str' is defined as an empty string. ...
BashBites:Check Files Check a file exists 1 2 3 4 5 6 7 1. 2. 3. 4. 5. 6. 7. #!/bin/bashif [[ -e /tmp/adb.log ]]then echo "Exists"else echo "Not Exists"fi 1. Check Empty String 1 2 3 4 5 6 1. 2. 3.
echo"the variable X is not the empty string" fi 运行这个脚本,输出如下: the variable X is not the empty string 为何?这是因为shell将$X展开为空字符串,表达式[-n]返回真值(因为改表达式没有提供参数)。再看这个脚本: 1 2 3 4 5 #!/bin/bash ...
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 "sam" ] && echo "True" || echo "False" ...
Check empty bash array with string comparison We are going to use two elements to check if bash array is empty or not. One is${#array[@]}and other is the-zoperator. Here, the${#array[@]}is used in Bash for array expansion, allowing you to access all elements of an array.Don't...
如果message为空,将打印parameter null or not set。清单 5-2 需要两个非空的命令行参数,并在它们缺失或为空时使用这个扩展来显示错误消息。 清单5-2。checkarg,如果参数未设置或为空,退出 ## Check for unset arguments : ${1?An argument is required} \ ${2?Two arguments are required} ## Check ...