Using Path.GetDirectoryName on command string with optional parameters and quotes

Question

Our clients have a string stored in their registry which is an executable command. The string may or may not have quotes around the target path, and may or may not have parameters. For example:

"C:\path\file.exe" param1=value1 param2=value2
C:\path\file.exe param1=value1 param2=value2
"C:\path\file.exe"
C:\path\file.exe
"C:\path\file with spaces.exe" param1=value1 param2=value2
"C:\path\file with spaces.exe"

I need to get the directory of the target path, i.e. C:\path.

I tried Path.GetDirectoryName, but that fails with "Illegal characters in path."
I also tried creating a ProcessStartInfo object, but that doesn't seem to have the smarts to parse the string.
I fiddled with Uri, but didn't have any luck there either.

I have a solution using a regular expression (which I will post below as an answer), but this seems like a "there-must-be-a-built-in-.Net-helper-class-for-this" problem.

Is there a class I'm missing, or just not using the classes above correctly?

Side topic... Can you put anything in these registry keys? — Austin Salonen
– Austin Salonen, Commented Jan 29, 2010 at 16:08
@Austin: We need the value as part of a custom action in a WiX install. The string is placed there by the previous installer software we were using. Thus, it's somewhat constrained, but the formats above are all possibilities. I'm not worried about handling the case where the value is not a valid command string. That will just fail. — Dave Mateer
– Dave Mateer, Commented Jan 29, 2010 at 16:14

Dave Mateer · Accepted Answer · 2010-01-29 16:03:06Z

1

Here's a regular expression that is working. But, like I said in my question, is there a better way? Or are there cases where this will fail?

Regex pattern = new Regex(@"^(?<quot>"")?(?<path>(?(quot)[^""]|\S)*)", RegexOptions.ExplicitCapture);
var match = pattern.Match(value);
return Path.GetDirectoryName(match.Groups["path"].Value);

answered Jan 29, 2010 at 16:03

Dave Mateer

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1 Comment

Lucero Over a year ago

Looks quite OK to me for the specific task at hand.

Ruben Bartelink · Accepted Answer · 2010-01-29 16:22:46Z

I had posted:

var strings = value.Split(" ", 2);
var firstString = strings.Length == 0 ? string.Empty : strings[0];
return Path.GetDirectoryName(firstString );

But then I slapped myself.

Then I saw http://community.bartdesmet.net/blogs/bart/archive/2009/02/21/net-4-0-system-shell-commandline-parsing-part-1.aspx any use? (doesnt look like it handles this aspect of the parsing though, and it doesnt actually exist!)

None of the standard System.IO classes provide any of the type of parsing you're looking for so I say your regex is fine unless someone can locate a common one.

Looking in Reflector, all the System.Environment code that does command line parsing seems to be Native, so I'd be pretty confident you're not missing any standard APIs for this purpose - this type of consideration (how file names are represented) is considered external to .NET (which makes sense as it's platform specific).

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