How does one set a variable variable?

[Seth Parker]

Is there a way to have a value of a shell variable be dependent on that of another?

For example:

MAIN=Sad
DEP=$MAIN" times"

echo $DEP would return "Sad times"

But what I'm looking for is if I were to next enter:

MAIN=Happy
echo $DEP would now return "Happy times"

I realize the above code won't give me what I want, but can something to this effect be accomplished? Any ideas?

Thanks,
Seth

[Patrick Wallek]

The above is possible, yes.

In a script, something like this:

#!/usr/bin/sh

MAIN="Sad"
OTHER=" times"

DEP=${MAIN}${OTHER}

echo ${DEP}

MAIN="Happy"

DEP=${MAIN}${OTHER}

echo ${DEP}

[Anil C. Sedha]

Seth,

It is very simple to do this.

You just have to specify the parameter every time you want a value out of it. Only care you have to take is that you don't re-specify the variable value till you have got the result of the first one.

The earlier post explains it nicely.

-Anil

[Rajeev Shukla]

Ya as said its very simple. Just assign both values to variables and play with them.
like
MAIN=Sad
TIM=times
then
echo $MAIN $TIM (will give Sad times)
and then
MAIN=happy

and echo $MAIN $TIM
would return happy times

Just give a try

Cheers
Rajeev

[Seth Parker]

I guess I should have expanded my original post a little. What I'm looking for is the exact behavior I described. When MAIN changes, so should the value of DEP. I don't want to have to reassign any variables but MAIN.

Does this make sense?

Thanks for the replies so far!

Seth

[Patrick Wallek]

I'm not sure you can have the type of behavior you require.

If you can, I don't know how to do it.

[MANOJ SRIVASTAVA]

Hi Seth

Since you are treating DEP as a vraible too you would need to reset the same in case you need to change $MAIN , the other was would be to use a shell scirpt to attaint eh same which can have if with 2 conditons.In the shell it wont be possible as the youy are dealing with two variables , and to set that you would need 2 statements not one.


Manoj Srivastava

[Martin Robinson · Accepted solution]

This can be done using the eval command.

Set DEP to a string that includes the name of the variable.
$ DEP="\$MAIN times"
This effectively defers evaluation of $MAIN.
$ echo $DEP
$MAIN times
MAIN=Sad
$ eval echo $DEP
Sad times
$ MAIN=Happy
$ eval echo $DEP
Happy times

Hope this helps.

[Carlos Fernandez Riera]

10 points for Martin:

Another example using awk:

export BOX1=yellow
export BOX2=lightgreen
export BOX3="#0080FF"

awk '{ color=ENVIRON[$1]
print "" $1 ""} ' <BOX1
BOX2
BOX3
END

[Seth Parker]

Nice, Martin! I'm going to see how I can fit that in to what I'm doing.

Thanks to you as well, Carlos. Nice example, but not quite what I was looking for.

And thanks to everyone else that took the time to reply.

Regards,
Seth