What is the command line length limit?

RE: What is the command line length limit?

Juan Miguel Venturello — Wed, 10 Dec 2003 20:30:00 GMT

Thanks for this blog Raymond, this is very interesting. Looking forward to the answers tomorrow, I can imagine what some of them will be ;) This weekend I went through all your blog archives and learnt many, many things I have always wondered about in my win32 developer career, and a few new tricks. As many said, this is book material :) Good luck with all and again, thanks, Juan Miguel Venturello

RE: What is the command line length limit?

Jordan Russell — Wed, 10 Dec 2003 22:57:00 GMT

I never knew ShellExecute imposed such a limitation. Very good to know. Here's an unrelated question that might make for an interesting blog topic: Why does FILE_ATTRIBUTE_NORMAL exist, and why is it defined as 0x00000080? Why not just use 0 when no special attributes are set?

RE: What is the command line length limit?

Catatonic — Wed, 10 Dec 2003 23:15:00 GMT

What is the limit for _spawnv(), where you supply your own argv to the process? I use this in my code because I don't have to worry about quoting or escaping special characters.

RE: What is the command line length limit?

Catatonic — Wed, 10 Dec 2003 23:18:00 GMT

Whoops, forgot to post the answer! The limit for _spawnv is a measly 1024 bytes.

RE: What is the command line length limit?

Anonymous — Wed, 10 Dec 2003 23:29:00 GMT

_spawnv eventually calls CreateProcess but there doesn't seem to be any limit checks before it calls it (at least in the CRT for VS6).

RE: What is the command line length limit?

Anonymous — Wed, 10 Dec 2003 23:36:00 GMT

The CRT for VS6 doesn't check for that limit at all. Infact, it doesn't even use arg_len in _cenvarg at all.

RE: What is the command line length limit?

Raymond Chen — Thu, 11 Dec 2003 01:08:00 GMT

For historical completeness: The DOS command line length limit was 127 characters.

RE: What is the command line length limit?

Catatonic — Thu, 11 Dec 2003 01:33:00 GMT

Interesting. The MSDN documentation for _spawnv must say 1024 bytes for a reason. Just to be safe I'd better stick to it!

RE: What is the command line length limit?

Mike Dunn — Thu, 11 Dec 2003 11:25:00 GMT

To pass > 32K chars, use a memory mapped file. You can pass the name of the MMF object (or a handle value, if you let the 2nd app inherit handles from the first) and the length of the memory block on the command line: # Pass 261004 bytes in the MMF called "MyMMFThingy" appnumber2.exe /n "MyMMFThingy" /l 261004 Then of course you add some sync code so that the MMF stays around for as long as both apps need it to.

RE: What is the command line length limit?

Raymond Chen — Thu, 11 Dec 2003 18:18:00 GMT

Mike got it basically right. Except that you don't want to pass the length on the command line; somebody could pass a bogus length and cause you to crash. And coming up with a unique name can be tricky (plus giving it a name opens you up to attackers who can grab the shared memory object file and look at or even mess with it before the child looks at it -- this is a data tampering / information disclosure attack; you can prevent this by applying ACLs to your shared memory object). I prefer an anonymous inheritable handle, which avoids the synchronization problem as well.

RE: What is the command line length limit?

Mi — Thu, 11 Dec 2003 18:45:00 GMT

RE: What is the command line length limit?

Mike Dunn — Thu, 11 Dec 2003 18:47:00 GMT

Both good points, Raymond. This teaches me that I shouldn't write code with security implications at 12:25 AM ;)

RE: What is the command line length limit?

James Curran — Fri, 12 Dec 2003 19:03:00 GMT

Raymond, I love the Code/History notes. Do you take requests? One of the bugaboos of Undocumented MSDOS coding was attempting to change the master environment variables block. (If I recall correctly, by DOS6, there were six different ways to find it -- none of which were guaranteed to work, so you had to try all six, and use the number which came up the most). Which bring us to the question -- Why did microsoft never provide a nice simple (say, INT 21h) interface to add & remove evars.

RE: What is the command line length limit?

Raymond Chen — Fri, 12 Dec 2003 20:15:00 GMT

Because you aren't supposed to change the environment of another process, much less the root environment block. Unix doesn't let you do it either.

Commenting on this entry has been closed.

Raymond Chen — Fri, 06 Aug 2004 17:53:00 GMT

Commenting closes after two weeks.

http://weblogs.asp.net/oldnewthing/archive/2004/02/21/77681.aspx

Dynamic FxCop Dependency List Using MSBuild

Paraesthesia — Fri, 20 Jun 2008 00:59:15 GMT

Dynamic FxCop Dependency List Using MSBuild