$mircdir is not static either. Someone moves mIRC to a different location and it changes..

If you use completely static directories by hardcoding them into your script (ie. you use /write "c:\program files\mirc\x.txt" a) then that's just the worst way possible. If I install mIRC to c:\mirc\, then I'm going to want settings stored somewhere around there. Not in an entirely different folder.