how do I chop of characters at the end of a line...

Forside
Vedhæftede filer:
Indlæg som e-mail
+ (text/plain)
Slet denne besked
Besvar denne besked
Skribent: Entelin
Dato:  
Emne: how do I chop of characters at the end of a line...
I want to take a variable say a="string.txt" and chop off the last 4
characters so I can make variable b equal to just "string"

Thanks for your help