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
在bash中,我们可以使用if语句结合条件判断来判断一个变量是否为空。具体的语法如下: ```bash if [ -z "$var" ]; then echo "Variable is empty" else echo "Variable is not empty" fi ``` 在上面的示例中,-z表示判断变量是否为空,$var是我们要判断的变量。如果变量var为空,则输出“Variable is empty...
In programming, it is essential to check if a variable is “set” or “not set,” which means you have to check if a bash script variable has a value or not. This check helps for effective data validation. However, there’s no built-in function for checking empty variables in bash sc...
在bash命令替换期间,如果变量为空,可以通过以下方式处理: 1. 使用默认值:可以使用`${variable:-default}`的语法,如果变量为空或未设置,则使用默认值。例如,`${var:-...
a non-empty string (1)# $JAIL set to the empty string (2)# $JAIL can be unset (3)###echo "*** Current value of \$JAIL is '$JAIL' ($HINT) ***" ## Determine if a bash variable is empty or not ##if [ -z "${JAIL}" ]; then echo "JAIL is unset or set to the...
1.变量通过“ ”引号引起来 如下所示，可以得到结果为 is null #!/bin/bash para1= if[!
if语法[Linux(bash_shell)] http://blog.csdn.net/ycl810921/article/details/4988778 1: 定义变量时, =号的两边不可以留空格. eg: gender=femal---right gender =femal---wrong gender= femal---wrong 2 条件测试语句 [ 符号的两边都要留空格.
$ ls -l | > while read perms links owner group size month day time file > do > printf "%10d %s\n" "$size" "$file" > totalsize=$(( ${totalsize:=0} + ${size:-0} )) > done $ echo ${totalsize-unset} ## print "unset" if variable is not set unset 通过使用进程替换,变量...
-v varname True if the shell variable varname is set (has been assigned a value, even an empty value). -R varname True if the shell variable varname is set and is a name reference. -z string True if the length of string is zero. ...
TestFile1 does not exist or is empty. 向文件添加一些内容,然后再测试一次: [student@studentvm1 testdir]$ 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." ...