if [ -z "$var" ]; then echo "var is blank"; else echo "var is set to '$var'"; fi 这通常是错误的,因为它不区分未设置的变量和设置为空字符串的变量。也就是说,如果var='' ,那么上面的解决方案将输出 “var is blank”。 unset 和 “设置为空字符串” 之间的区别在用户必须指定扩展名或...
In both examples, we used the if statement with the -z option to check if the variable is empty. Here, the -z option is a unary test operator that checks if the string is empty. This operator accepts one argument that is a string to be tested; it returns true (0 exist status) if...
Use the if-else statement with the -v option to check if an environment variable is set in bash. The echo command in the if block will be executed if the will
- Testifa 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: [[$variable-eq|ne|gt|lt|ge|leinteger]] - Testifthe specified variable has a [n]on-empty value: [[ -n$vari...
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: ...
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 代码运行次数:0 运行 AI代码解释 #!/bin/bash a=60100 sw...
variable=$'这是第一行\n这是第二行' 这样,变量"variable"的值也将包含两行文本,通过"\n"进行换行。 需要注意的是,在使用这些方法时,需要确保脚本中的换行符在输出时能够被正确解释。可以使用echo命令来输出变量的值,并使用-e选项来解释转义字符。例如: 代码语言:txt 复制 echo -e $variable 这样,将会按照...
The-zoperator returnstrueif a string variable is null or empty. How the use the-zBash Operator Afterdeclaring a string variable, use the-zoperator in anif statementto check whether a string is empty or not: MY_STRING="" if [ -z $MYSTRING ] ...
= 等于,如:if [ "a"="b" ] == 等于,如:if [ "a"=="b" ],与=等价 注意:==的功能在[[]]和[]中的行为是不同的,如下: [[ a == z* ]] # 如果a以"z"开头(模式匹配)那么将为true [[ a == "z*" ]] # 如果a等于z*(字符匹配),那么结果为true ...
The operator return an exit code 0 (True) if the strings match the regular expression regex. The $BASH_REMATCH environment variable is a read-only Bash Array containing the values matched by the extended regular expression at the right side of the =~ binary operator in a double-bracket [[...