Creating Compressed Directory

Often times I find myself in need of creating a directory with compressed attribute turned on, so I can put some text log files in with less space consumption.  While md or mkdir doesn't support doing this directly, you can create the directory and later apply the compression attribute, so that any subsequent files copied to that directory will be compressed.

md SomeDir

compact /C SomeDir

copy SomeText.log SomeDir

That does it.  Not the most useful thing in the world.  But hey, you never know when you will need it.

Out Parameter In Function Call

Let's say you write a function or procedure or sub program or whatever you want to call it in batch.  How do you pass back a value to the caller?  You can of course set an environment variable, but that's like setting a global variable.  And that's not very nice if you need to call the function multiple times and only use the value after all function calls are made.

Consider this example:

@echo off

call :GETVALUE

set INPUT1=%USERINPUT%

call :GETVALUE

set INPUT2=%USERINPUT%

echo %INPUT1% %INPUT2%

goto :EOF

 

:GETVALUE

set /P USERINPUT=Input?

goto :EOF

Like I said, it's doable, but not very nice.  I find it more soothing to the eyes if I can pass the variable name as an argument to the function.  And here's how you do it:

@echo off

call :GETVALUE INPUT1

call :GETVALUE INPUT2

echo %INPUT1% %INPUT2%

goto :EOF

 

:GETVALUE

set /P %1=Input?

goto :EOF

Nice and simple.  All you need to do is remember that you can use %1 and other %<number> on the left hand side of an assignment.  And it makes you think for a second that you are programming a real scripting language.

Escape Characters

I know this is going to be a confusing year, because my first post of this year is on a topic I don't really understand.

For some time now I have been confused what the correct method to escape certain characters from being interpreted when I try to print them out.  Let's say I want to print this line:

< & >

I can't just say

echo < & >

Because I'll get an error that way (try it yourself if you don't believe me).  I have to escape those special characters.  To do that I can use the caret (^).

echo ^< ^& ^>

Nice and easy.  But then if I want to print this line:

%SYSTEMDRIVE%

The batch interpreter does something really baffling.  If I'm doing it from command line, I can escape it with a caret like other special characters.

echo ^%SYSTEMDRIVE^%

But it I do it from inside a batch file, that no longer works.  I have to escape the % not with a caret, but with another %.

echo %%SYSTEMDRIVE%

Confuse the hell out of me, I tell you.  So now I live by these rules:

1. Always escape special characters using a caret in front of the special character.
2. Except when you are in a batch file and need to escape a %, then use a %%.

I hope that helps some of you.  Oh wait, nobody reads this blog but me.  Oh, well.