In "real DOS", the GOTO command is used to skip part of a batch file:
@ECHO OFF • • CHOICE /C:123 /N Choose 1, 2 or 3 IF ERRORLEVEL 3 GOTO Label3 IF ERRORLEVEL 2 GOTO Label2 IF ERRORLEVEL 1 GOTO Label1 • • :Label1 ECHO You chose 1 GOTO End :Label2 ECHO You chose 2 GOTO End :Label3 ECHO You chose 3 GOTO End • • :End
The same goes for OS/2 and its DOS box.
Combined with IF and by "nesting" GOTOs, one can easily create true "spaghetti code" which is a disaster to read and debug.
Compare this to "real" subroutines (or functions in Pascal, or procedures in Rexx), that can be used and called as independent functions within the program you are creating.
There is, of course, always a way to fake subroutines in batch files:
@ECHO OFF • • :: First call of Sub5 subroutine SET RETURN=Label3 GOTO Sub5 :Label3 • • :: Second call of Sub5 subroutine SET RETURN=Label4 GOTO Sub5 :Label4 • • :: End of main program GOTO End • • :: Sub5 subroutine starts here :Sub5 • (some code to do whatever • it is Sub5 should do) :: End of Sub5 subroutine :: (emulated "Return") GOTO %RETURN% • • :: End of batch file :End
The real surprise here is (once more) Windows NT.
In NT, a call to a subroutine's label (
CALL :label), combined with
GOTO :EOF to terminate the subroutine, presents a way to create real subroutines,
GOTO :EOF being the instruction to jump back to where the subroutine was called.
@ECHO OFF • • :: First call of Sub5 subroutine IF "X"=="%Y%" CALL :Sub5 • • :: Second call of Sub5 subroutine IF "Z"=="%Y%" CALL :Sub5 • • :: End of main program GOTO End • • :: Sub5 subroutine starts here :Sub5 • (some code to do whatever • it is Sub5 should do) :: End of Sub5 subroutine GOTO :EOF • • :: End of batch file :End
The most difficult part of subroutines is usually deciding which part of the program's code goes into which subroutine.
|Note:||A final note on labels in batch files:
Always terminate a label with a line feed, or ("true") DOS won't be able to find it.
|page last uploaded: 2015-08-24, 21:10|