Help with null variables

[Wrathchild]

What's the best way to check to see if variables are Null? I have a script with approx. 9 variables and I would like to only use them in the commands if they are set. I played around with -n but it errored when the variable was null.

 

[PHV]

man test
A starting point:
[ -z "$varName" ] && echo varName not set

Hope This Helps, PH.
Want to get great answers to your Tek-Tips questions? Have a look at FAQ219-2884 or FAQ181-2886

 

[cspilman]

if [ "$VAR_NAME" ] ; then
command...
fi



Regards,
Chuck

 

[LKBrwnDBA]

Maybe you would like to assign default values if the variables are null:

VAR_NAME=${VAR_NAME:='DefaultValue'}

----------------------------------------------------------------------------
The person who says it can't be done should not interrupt the person doing it. -- Chinese proverb

 

[SamBones]

If you're testing for command line parameters, I usually do something like this...

#!/bin/ksh

VAR1=${1:-MISSING}

if [[ "${VAR1}" = "MISSING" ]]
then
    <do some stuff>
fi

It "reads" well so it's easy to debug or someone else to maintain.

 

[Wrathchild]

ok, I have a variable called "test"
I made a script with the following:

if [ -z "$test" ]
then
rm filename
fi

I've set:
test=
test=""
test="asdf"

In all 3 situations the file gets removed...am I missing something?

 

[hoinz]

It seems your script is executed in a subshell, and your variable test is not exported.
For example, if you define test=abc on your command line, and then you call your script, a new shell will be started, and the new shell will not know about this variable.
There are two possible solutions:

1) Define the varible test within the same script where you have if [ -z "$test" ]
- or -
2) Export the variable test to subshells:
export test=abc
(Syntax my differ, depending on your shell.)

hope this helps

 

[Wrathchild]

including the variable in the script did the trick, thanks all!