["$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:["$variable" ] || exit。 如果变量未设置或设置为
#!/bin/bash # Set the variable variable="" # Check if the variable is empty if [ -z "$variable" ]; then echo "Variable is empty." else echo "Variable is not empty." fi Copy Save changes and exit from the nano text editor. Finally, use the chmod command to make the file execut...
```bash if [ -z "$b" -a "${bxxx}" = "xxx" ] # 这里的判断会有单独的文章介绍 then echo 'b is set but empty'; # 设置但为空 else echo 'b is not set'; # 没设置,如 c fi``` 变量中的空格 代码语言:javascript 代码运行次数:0 运行 AI代码解释 e=123# 报错,变量中间当然不能有...
VARIABLE= value # 脚本将会尝试运行 "value" 命令,同时设置环境变量 "VARIABLE" 为 ""。上面 $b 和 $c 的区别?...but empty'; # 设置但为空 else echo 'b is not set'; # 没设置,如 c fi ``` 变量中的空格 e=1 2 3 # 报错,变量中间当然不能有空格 e=...如果在变量中出现空格,那么必须...
;;esacdone# MANUAL_VARS_SPEC: Change the varibles to the appropriate values if you do not wish to use the comman line options.# These are essentially the default settings of the script.# folder for input filesif[ -n"$inps_folder"];then# "if the commandline option is an empty string...
# 这里会出现一个误区 [ ${emptyvar} = "" ],这个等于 [ = "" ],所以会报错 # 而下面的2个方法都是可行的 emptyvar= if [ "${emptyvar}" = "" ]; then echo "empty var" fi if [ -z ${emptyvar} ]; then echo "empty var" ...
$mvvariable showvar $ ./showvar $x is not set $ x=3$ ./showvar $x is not set $ export x=4$ ./showvar $x=4$ x=## bash中,对一个变量重新赋值,并不会从环境变量中移除该变量 $ ./showvar $x is set but empty 设置在子shell中的变量对调用它的脚本不可见。子shell包含命令替换,如...
How To Bash Shell Find Out If a Variable Is Empty Or Not #!/bin/bashJAIL="/nginx"HINT=""# Do three possibilities for $JAIL ##for i in 1 2 3 docase $i in1) JAIL="/nginx/jail"; HINT="value set";;2) JAIL=""; HINT="value set to empty string";;3) unset JAIL; HINT="...
if [ -z "$1" ]; then # empty string rval="" return fi # wc puts some space behind the output this is why we need sed: numofchar=`echo -n "$1" | wc -c | sed 's/ //g' ` if [ "$numofchar" = "1" ]; then
bash command if a string is not empty examples of the check when DiskInternals can help you Are you ready? Let's read! Variables that are set and not empty A variable is either defined or not defined. However, when a variable is defined but has no value, then the variable is “Not ...