在这个示例中,$variable是要检查的变量。如果它为空,则打印"Variable is empty";否则,打印"Variable is not empty"。 使用双引号和等号 另一种常见的方法是使用双引号和等号进行比较。 以下是示例代码: if["$variable"=""];thenecho"Variable is empty"elseecho"Variable is not empty"fi 在这个示例中,$vari...
if[!-z"$variable"];thenecho"Variable is not empty"elseecho"Variable is empty"fi 在这个示例中,$variable是要检查的变量。如果它不为空,则打印"Variable is not empty";否则,打印"Variable is empty"。 使用条件表达式检查变量是否为空 除了if 语句,还可以使用条件表达式来检查变量是否为空。条件表达式可以...
There are several reasons why one would want to check whether the variable is empty, such as checking for input validation. And in this tutorial, I will show you 4 ways to check how to check if the variable is empty in bash: By checking the length of the variable Using non-empty check...
Checking If Variable Is Empty in Bash There are multiple ways to check if a variable is empty or not. Before moving towards those methods, knowing when a variable is called empty is necessary. In Bash, a variable is called empty if: A variable is declared without assigning any value to ...
常见$(variable) 3 初始化数组 array=(a b c d) 接下来是一个demo,内含详细注释 #!/bin/bash # 单方括号内可以使用变量 SWAP_DEVICE=/dev/sda1 if [ ${SWAP_DEVICE} == "/dev/sda1" ]; then echo "单方括号内可以使用变量" fi # 双方括号内可以使用变量 ...
- Test if a 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: [[ $variable -eq|ne|gt|lt|ge|le integer ]] - Test if the specified variable has a [n]on-empty value:...
["$variable" ] || echo empty : ${variable="value_to_set_if_unset"} 相关讨论 默认VaR的好方法,加上1 @ehime设置默认值时,您将使用${variable:-default_value}。 这是一种快速检查变量条目有效性的方法,如果没有设置,则退出:["$variable" ] || exit。 如果变量未设置或设置为空字符串("),则返...
- Testifa given variable is [eq]ual/[n]ot [e]qual/[g]reater [t]han/[l]ess [t]han/[g]reater than or [e]qual/[l]ess than or [e]qual to the specified number: [[$variable-eq|ne|gt|lt|ge|leinteger]] - Testifthe specified variable has a [n]on-empty value: ...
if [ -n "$variable" ]; then echo "variable is set and not empty" fi 在上面的示例中,我们只检查$variable是否有值。如果变量被设置且不为空,则执行echo语句。 总结 在Bash中,我们可以使用-z操作符来检查变量是否被设置,使用-n操作符和$variable的值来检查变量是否被设置并且非空,或者只使用-n操作符和...
TestFile1 does not exist or is empty. 向文件添加一些内容,然后再测试一次: [student@studentvm1 testdir]$ File="TestFile1" ; echo "This is file $File" > $File ; if [ -s $File ] ; then echo "$File exists and contains data." ; else echo "$File does not exist or is empty." ...