FOR command gives error, but only when using colons for comments

Some references:
http://www.robvanderwoude.com/comments.html
http://www.windowsitpro.com/Article/ArticleID/13453/13453.html

I think it's important to point out that XP uses cmd.exe, not command.com by default.  The second link simply sites "easier to read" as the reasoning for use ::.  If you are having problems with :: then I suggest it's because it wasn't designed to be a remark character.  It happens to be usable at times, but it would stand to reason to me that using : as a remark character would actually slow things down because the batch file would have to remember what every instance of : said in order to use it to "goto" when appropriate or if not remember, then have to reread the file whenever a goto was encountered.  REMs should be ignored entirely.

Thanks for the responses.  I've used double-colons in other spots in my script with no problems.

leew is correct in his first post.
The first colon by definition creates a "label" for CALL or GOTO to be able to jump to.
The word after that is the identification of that specific label - must be unique to function correctly.
The second colon closes the identification and everything after that on the line is ignored by the parser.  

Starting with two colons together creates a null label that is useless.  It has interesting side effects of NOT expanding variables included on that line. It's not a statement like REM, it's a nul label with ignored characters after it.   Also special characters that can cause execution errors when used in REM statements do not cause errors when included on a null label line.  REM is a statement and as such is parsed.  That takes more time than ignoring a text on a null label line, but if that very tiny difference is important to you then you need a better languange than batch commands anyway, so feel free to use REM.  

It's the way ( ) sends all encluded lines through a new instance of the CMD interpreter that causes lines beginning with :: to fail.  
I aggree with SunBow -  if at all possible, you should put remarks before the FOR statement to prevent the parser from re-hashing the REM statement during every time the do ( ) loops around.  If your ( ) loop is SOOO long you MUST use explanations inside, then use REM.  

- I wouldn't want to mention the sideeffect of the first interpreter ignoring a third colon as just another character after the nul label and passing it to the loop with the rest of the line.  The (  ) generated interpreter uses colons 2 and 3 as if they are 1 and 2 in the child process. Code like this has been shown to work, but you will not see it in any of my stuff (i hope):
(
echo test 1
::: echo this line ignored - you will not see it echoed.
rem  this works just as well but parses again for each loop
echo done
)

   
leew and sunbow were first with correct answers, - I only added this in hopes of making the difference more clear.

As for second colon implying a drive letter, that's just a human perception thing.  Drive letters are only concidered as such when used in context of a file name, reguardless of weather first on a line or in the middle, or surrounded by quotes.  This demonstrates the interpreter believing in a drive letter that is not a drive letter at all (test.txt and server named test do not need to exist for this to work) :
for %%K in ( C:test.txt  \\test\test.txt ) do echo %%K is on drive: %%~dK


good luck (\o/)

Well said Steve,  now we all know i type slow and took at least an hour to get that in there,  lol.
Would you believe i was interrupted several times by a herd of wild horses?

would you believe instead only twice by my lovely wife?

Just my two cents:

Does it honestly make that much difference that a REM statement is processed? On an old 386 every cycle counted, but in these days of 3+GHz processors, pretty much anything run in a CMD script runs at blinding speed. Unless it's an:
      Embedded
            Embedded
                  Embedded
                        Remark

I don't think it will cause great pain. Just look at SteveGTR's tests - 10,000 REMs took 2 seconds...

If a batch file takes an age to run, it's probably the commands you're calling, not the remarks.

Wallsy

Hi, thanks for all the responses and insight....

I had previously searched this site and couldn't find the issue in the PAQs, but after SteveGTR said it had been discussed before, I tried again and finally found it here: http://www.experts-exchange.com/Operating_Systems/MSDOS/Q_21045653.html

As for using REM exclusively for comments:

http://www.obrienpc.net/dos/y-rem.html says that REM can screw up batch files when the commented line contains a pipe (|) or redirection (<, >, >>) symbol, at least in DOS 7.  However I tested their example of:

REM echo. | date

and this gave me no problems on WinXP.

So now I plan to use REM all the time.

I agree that the speed issue is not anything to worry about (at least for my tiny scripts).  I mostly liked the colons because my scripts were easier to read!  ;)

Thanks again--

Dave

Thanks                            [Good Fortune]

Concerning readability, add at least some extra blank lines. Spaces (tabs..) are also good if conducive to columns. I like a <CR> immediately before and after a series (group) of lines, whether they are of a loop, or comments, or whatever (set variables?)