["$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:["$variable" ] || exit。 如果变量未设置或设置为空字符串("),则返...
/bin/bash # Set the variable variable="" # Check if the variable is empty if [ -z "$variable" ]; then echo "Variable is empty." else echo "Variable is not empty." fi Save changes and exit from the nanotext editor. Finally,use the chmod command to make the file executableas ...
[ "$variable" ] || echo empty : ${variable="value_to_set_if_unset"} Run Code Online (Sandbox Code Playgroud) 3ks*_*stc 7 true如果未设置变量或将变量设置为空字符串(""),则会返回此值. if [ -z "$MyVar" ] then echo "The variable MyVar has nothing in it." elif ! [ -z "$...
If yes, then print the value. If no, then use the default value “Greenland”. Basically, we’re setting a default value that will be used when the variable is not set or have anullvalue. Method 3 – Assigning default value to empty variable This section will showcase how to assign ...
if [ -z "$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
# 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
在Bash中为变量赋值非常简单。基本语法是将变量名与等号(=)连接,然后在等号右边放置变量的值。需要注意的是,在变量名和等号之间不能有空格。以下是一些示例: ```bash # 为变量赋值 my_v...