DEV Community

Tomasz Wegrzanowski
Tomasz Wegrzanowski

Posted on

100 Languages Speedrun: Episode 72: Windows Batch Files

#dos #windows

Batch Files, with extension .bat, were DOS equivalent of shell scripts.

DOS version (still used by DOSBox) was extremely limited, and couldn't even add numbers. Starting with OS/2 and Windows NT, .bat files were extended with some very rudimentary scripting capabilities, so that's what we'll be doing today, but I'll limit my use of these extended features to just set /a for math.

You can run these examples on any Windows machine. Due to set /a they won't work on a DOSBox, or on a DOS machine if you somehow still have one.

Hello, World!

We can start by writing hello.bat:

echo Hello, World!
Enter fullscreen mode Exit fullscreen mode

Unfortunately it does a very annoying thing, and echos every command before executing it. That's fine for debugging, but not really what we want most of the time:

C:\> hello C:\> echo Hello, World! Hello, World! C:\>
Enter fullscreen mode Exit fullscreen mode

We can modify this by putting @ before the command, or we can just disable command echo-ing completely with @echo off.

@echo off echo Hello, World!
Enter fullscreen mode Exit fullscreen mode 
C:\> hello2 Hello, World! C:\>
Enter fullscreen mode Exit fullscreen mode

I'm still not sure where that extra newline is coming from, but let's not worry about it for now.

Variables

We can set variables with set name=value, and insert them into other commands with %name%.

@echo off set name=Alice echo Hello, %name%!
Enter fullscreen mode Exit fullscreen mode 
C:\> vars Hello, Alice! C:\>
Enter fullscreen mode Exit fullscreen mode

This is about the point where we could still run those examples on DOSBox or a DOS machine. From this point on, it's all Windows extensions.

Math

DOS .bat files had no way to do math, but Windows added set /a for it:

@echo off set /a a = 40 set /a b = 380 set /a c = %a% + %b% echo %c%
Enter fullscreen mode Exit fullscreen mode 
C:\> math 420 C:\>
Enter fullscreen mode Exit fullscreen mode

Loop 

@echo off set /a i = 1 :loop echo %i% set /a i = 1 + %i% if %i% neq 11 goto :loop
Enter fullscreen mode Exit fullscreen mode 
C:\> loop 1 2 3 4 5 6 7 8 9 10 C:\>
Enter fullscreen mode Exit fullscreen mode

What's going on here:

  • we set initial value of i to 1
  • we have a label :loop
  • every iteration we echo current value of i
  • then we increase i by 1
  • if i is not equal to 11, we jump to :loop

Fibonacci

Functions are hard, so let's do iterative solution. We just do a bunch of variable assignments and additions in a loop. We don't need any new features here:

@echo off set /a i = 1 set /a a = 1 set /a b = 1 :loop echo fib(%i%)=%a% set /a i = 1 + %i% set /a c = %a% + %b% set /a a = %b% set /a b = %c% if %i% neq 21 goto :loop
Enter fullscreen mode Exit fullscreen mode 
C:\> fib fib(1)=1 fib(2)=1 fib(3)=2 fib(4)=3 fib(5)=5 fib(6)=8 fib(7)=13 fib(8)=21 fib(9)=34 fib(10)=55 fib(11)=89 fib(12)=144 fib(13)=233 fib(14)=377 fib(15)=610 fib(16)=987 fib(17)=1597 fib(18)=2584 fib(19)=4181 fib(20)=6765 C:\>
Enter fullscreen mode Exit fullscreen mode

FizzBuzz 

@echo off set /a i = 1 :loop set /a fizzbuzz = %i% %% 15 set /a fizz = %i% %% 3 set /a buzz = %i% %% 5 set /a t = %i% if %fizz% == 0 set t=Fizz if %buzz% == 0 set t=Buzz if %fizzbuzz% == 0 set t=FizzBuzz echo %t% set /a i = 1 + %i% if %i% neq 101 goto :loop
Enter fullscreen mode Exit fullscreen mode 
C:\>fizzbuzz 1 2 Fizz 4 Buzz Fizz 7 8 Fizz Buzz 11 Fizz 13 14 FizzBuzz 16 17 Fizz 19 Buzz ...
Enter fullscreen mode Exit fullscreen mode

We can do set conditionally just like we can do goto.

FizzBuzz, modern version

So far I used just DOS features and set /a. But Windows added a lot of features to .bat files - carefully gating them behind extra sigils and switches to maintain backwards compatibility.

If we wanted to use all the features, here's what FizzBuzz would be like:

@echo off setlocal enableDelayedExpansion for /l %%j in (1 1 100) do ( set /a fizz = %%j %% 3 set /a buzz = %%j %% 5 set /a fizzbuzz = %%j %% 15 if !fizzbuzz! == 0 ( echo FizzBuzz ) else if !buzz! == 0 ( echo Buzz ) else if !fizz! == 0 ( echo Fizz ) else ( echo %%j ) )
Enter fullscreen mode Exit fullscreen mode

But at this point we might just as well use PowerShell.

Should you use Windows Batch Files?

No. If you need to script a Windows machine, PowerShell is already there for you. And if it's something more complex, you might just as well use a real programming language.

Code

All code examples for the series will be in this repository.

Code for the Windows Batch Files episode is available here.

Top comments (0)