need someone (...or at least when you need a piece of data). Type 'set' in DOS. Notice the list. Now type 'set foo=bar'. You just set the variable FOO equal to BAR. Type 'set' again to see your evil doings. What is that good for you say? Everthing. Type 'echo %FOO%'. Notice that it echos the value of the variable FOO which we set to BAR. Command.com evaluates the letters inbetween the percentage signs and replaces the variable with the contents of the memory space named "FOO". It's bait and switch man, bait and switch.
Now comes the bad news. You can't do math in DOS batch. You can add in NT batch, but that's not the title of this tutorial. Try 'set num=1' & then 'set num=%num%+1'. It should be two you
say? Ha! 1+1=1+1 in DOS batch. Type 'echo %num%' to find that you have never seen such a thing since that Taoist monk in math class.
If only we could if. In DOS type: 'if 1==1 echo
yeppers'. Since "1" is exactly the same text as "1", Command.com executes "echo yeppers" which we know will just spit out "yeppers". If we use 'if 1==1.0 echo
yeppers', it just won't work. Why the double equal sign? Type 'if /?'. Because Big Brother says so.
Before we hit the loops, we need to arm you with something. Ctrl+C. If you hold Ctrl
and hit C, it will break the loop. Ctrl+Break will do the same thing. Use them well. Otherwise, you'll be burning countless CPU cycles wondering "Why do I feel like I've been here
before?". Let's go into Notepad and do a File>New to start a new horror. Type:
@ECHO OFF
REM Das Loop V1.0
SET MAX=..............................
REM Labels start with a colon.
:MOREDOTS
SET DOTS=%DOTS%.
ECHO %DOTS%
IF %DOTS%==%MAX% GOTO NOMOREDOTS
GOTO MOREDOTS
REM Command.com will jump to this label if %DOTS% equals %MAX% that we set earlier
:NOMOREDOTS
ECHO.
ECHO I've really had enough dots, thanks.
ECHO.
Breakdown: SET DOTS=%DOTS%. adds one period to the end of the variable dots, which is blank at first. It is now one dot. The next pass comes around,
replaces %DOTS% with one period and adds a period on the end. This goes on until %DOTS% becomes equal to %MAX% when we jump to the label called NOMOREDOTS.
Save this beaut as C:\WINDOWS\DESKTOP\DOTS.BAT
Notice the caps in dots.bat? It sometimes is easier since Command.com is not case sensitive. It's good practice to use caps in everywhere but in the user prompts and comments. BECAUSE WHO WANTS TO READ
THIS ALL THE TIME?
Now try running dots. Runs great. A neat little loop. Try running it again. Your first very own software bug! Now you know what it's like to be an easy target like
Microsoft. Type 'set' to see that the variable DOTS never reset itself. It's still in memory so it kept adding to itself. To fix this little oversight, put a 'SET DOTS=' above the 'SET
MAX=..............................' Doing a SET (Variable)= clears out the variable from memory.
Variables will reset themselves once you exit that instance of our friend, Command.com. Try setting some
variables and exiting Command.com by typing 'Exit'. If you run Command.com again, the variable won't be set.
So how do you set a variable to always be set? You can modify Autoexec.bat. With your
newfound batching skills, you'll make short work of it.
