How to detect if an environment-variable exists?

Hi,
( I'm new to NSIS, but I've searched the wiki & faq.
Many examples show reading & setting env-vars. )

How do I find out if an environment varible is set/exists?

The expression: $%MyOptionalEnv% will return the env-var's value, if the env-var exists.
But can I use !ifdef on that in some way?

If the env-var is not set, i understand it will have a value equal to its symbolic-text. But if I do a value compare with "$%MyOptionalEnv%" i can't make it work correctly.

This could be my being dumb, and not being able to escape strings correctly.

What is the best way to do this?

Many Thanks

You could try !if "$%foo%" != "$$%foo%" , if that does not work, you are going to have to use !system

No, "$$%foo%" does not work.
This is how I solved it:

!searchreplace MyOptionalEnv "$%MyOptionalEnv%" "%" "#"

!if "${MyOptionalEnv}" == "$#MyOptionalEnv#"

   !echo "MyOptionalEnv not found"

!else

   !echo "MyOptionalEnv found: ${MyOptionalEnv}"

!endif

Please note that this check runs at compile time, but since you mentioned $%MyOptionalEnv%, I assumed that is what you want.

Well it is "tad ugly" but it works! :-)

Thanks!

(sorry for late thanks, didn't get chance to try it for ages)