A method of determining whether an input variable or an argument is null in a shell script _linux shell

1. Judging variables

Copy Code code as follows:

Read-p "Input a word:" Word
if [!-n "$word"]; then
echo "You have not input a word!"
Else
echo "The word you are $word"
Fi

2. Judging input parameters

Copy Code code as follows:

#!/bin/bash
if [!-n ' $ ']; then
echo "You have not input a word!"
Else
echo "The word you are the input is $"
Fi

The following is not validated.

3. Directly through the variable judgment

As follows: The result is NULL

Copy Code code as follows:

#!/bin/sh
para1=
if [! $para 1]; Then
echo "is NULL"
Else
echo "Not NULL"
Fi

4. Use test to judge

The result is that DMin is not set!

Copy Code code as follows:

#!/bin/sh
dmin=
If Test-z "$dmin"
Then
echo "DMin is not set!"
Else
echo "DMin is set!"
Fi

5. Use "" to determine

Copy Code code as follows:

#!/bin/sh
dmin=
If ["$dmin" = ""]
Then
echo "DMin is not set!"
Else
echo "DMin is set!"
Fi

Here's a little bit of scripting code I wrote in a project that I used when the system started:

Copy Code code as follows:

#! /bin/bash

echo "Input Param is [$]"

if [!-n ' $ ']; then
echo "You have not input a null word!"
./app1; /APP12;. /app123
elif [$1-eq 2];then
./app12; /app123
elif [$1-eq];then
echo "YY";
Fi