Shell to determine if a variable is empty

Determines whether a variable is empty.

1. The variable is caused by "" quotation marks

As shown below:, you can get the result is NULL.

#!/bin/sh

para1=

if [!-n "$para 1"]; Then

echo "is NULL"

Else

echo "Not NULL"

Fi

2. Judging directly by variables

The results are as follows: Is NULL

#!/bin/sh

para1=

if [! $para 1]; Then

echo "is NULL"

Else

echo "Not NULL"

Fi

3. Use test to determine

The results are: DMin is not set!

#!/bin/sh

dmin=

If Test-z "$dmin" Then

echo "DMin is not set!"

Else

echo "DMin is set!"

Fi

4. Use "" to determine

#!/bin/sh

dmin=

If ["$dmin" = ""]; Then

echo "DMin is not set!"

Else

echo "DMin is set!"

Fi

PS: Description of the comparison of the number and determine whether it is empty best add "" in the outer layer, which avoids the problem of comparing the times with other characters.

This article is from the IT Network Tanuvi blog, be sure to keep this source http://03301216.blog.51cto.com/4550876/1767845

Shell to determine if a variable is empty