Check to see if a variable is empty or not Create a new bash file, named, and enter the script below. The script above stores the first command-line argument in a variable and then tests the argument in the next statement. This script will print the first argument because it is not em...
In this method, I will be using the-nflag to check whether the variable is empty or not. Here's the simple script which will tell me whether the variable is empty or non-empty: #!/bin/bash variable="" if [ -n "$variable" ]; then echo "Variable is not empty." else echo "Vari...
The“-n”option is used to check if a variable is not empty. We can use this option to check if the input argument exists or not. Below I have given an example code that checks if an input argument exists using the“-n”option: #!/bin/bash if[-n"$1"] then echo"Input argument ...
possibly to the empty string"fiif [ -n "${JAIL-unset}" ]; then echo "JAIL is either unset or set to a non-empty string"fidone## syntax 1 ##if [[ -z "$variable" ]]; then echo "Empty $variable"else echo "Do whatever you want as ...
$ unset x $ showvar $x is not set $ x=3 $ showvar $x is not set $ export x $ showvar $x = 3 $ x= ## in bash, reassignment doesn't remove a variable from the environment $ showvar $x is set but empty 注意 showvar不是一个 bash 命令,而是一个如清单 5-1 所示的脚本,...
/bin/bash#Simple program with a variableROUTERIP="10.0.0.1"printf"The router IP address:$ROUTERIP\n" 运行之后发现权限不够 ,需要给文件添加权限 chmod+x test.sh#给文件添加执行权限 重新执行后发现,脚本文件就可以被执行了 刚刚构建了第一个 Bash 脚本!假设我们希望该脚本自动运行,然后在系统中的任何...
empty string variable “val” first. After this, we have been using the “-n” option within the “if” part of the “if-else” statement within the square brackets. This option is checking whether the length of variable “val” is other than zero or not. If the length of variable ...
Afterdeclaring a string variable, use the-zoperator in anif statementto check whether a string is empty or not: MY_STRING="" if [ -z $MYSTRING ] then echo "String is empty" else echo "String is not empty" fi For more Shell scripting tips,check out or Bash/Shell scripting articles!
bash 中的条件语句，基础就是 Test 。 if 先来个实例： x=5; if [ $x = 5 ]; then e...
"which is not read as a comment. First line is also a place where you put your interpreter which is in this case: /bin/bash. Here is our first bash shell script example: #!/bin/bash # declare STRING variable STRING="Hello World" #print variable on a screen echo $STRING...