How to read an entire file into a string variable?

Try this:

Bank = LoadFileToBank("Filename.txt")
Result = FindTextInBank("some text",Bank)
If Result = 0
	Notify "String not found!"
Else
	Notify "Result found at offset " + Result
EndIf

Function LoadFileToBank(Filename$)
	FILE = ReadFile(Filename)
	BankID = CreateBank(FileSize(Filename))
	ReadBytes BankID,FILE,0,BankSize(BankID)
	CloseFile FILE
	Return BankID
End Function

Function FindTextInBank(Txt$,BankID,Start = 0)
	Ptr = Start
	Repeat
		T$ = Chr$(PeekByte(BankID,Ptr))
		If T$ = Left$(Txt$,1)
			For N = 1 To Len(Txt$)-1
				T$ = T$ + Chr$(PeekByte(BankID,Ptr+N))
				If T$ = Txt$ Then Exit
			Next	
		EndIf
		Ptr = Ptr + 1
	Until Ptr >= BankSize(BankID) Or T$ = Txt$
	If T$ = Txt$
		Return Ptr
	Else
		Return False
	EndIf
End Function

It works. Don't know how fast it is with big files though...

[EDIT] Just did a test on a 170k file - took ~4s to find a text string right near the end of the file.

I haven't really used banks before - there's probably a way of optimising this so that it works in a fraction of the time it currently takes.

[EDIT 2] Try it with debug off! Same test as above takes about 0.3s. :))