sugar logic function: strReplace()

Hello there,

anybody please help with the strReplace?

I want to replace two characters inside a word: " " and "-" via Studio-->module--->fields---->edit formula(using logic function).

But when I write:  strReplace([" ","-"],"",$field)  it doesn't work....

How can I do that, please?

One more thing, if I will repeatably use one calculated result, can I create a variable there? Like this: 

$t = strReplace(" ","",$field)


it looks like, I will get error...

Thanks in advance for any help!