Recipe 11.16 Parsing Paths in Environment Variables

Problem

You need to parse multiple paths contained in environment variables, such as PATH or Include.

Solution

You can use the Path.PathSeparator field or the ; character to extract individual paths from an environment variable whose value consists of multiple paths, and place them in an array. Then you can use a foreach loop to iterate over each individual path in the PATH environment variable and parse each path. This process is illustrated by the ParsePathEnvironmentVariable method:

public static void ParsePathEnvironmentVariable( )
{
    string originalPathEnv = Environment.GetEnvironmentVariable("PATH");
    string[] paths = originalPathEnv.Split(new char[1] {Path.PathSeparator});
    foreach (string s in paths)
    {
        string pathEnv = Environment.ExpandEnvironmentVariables(s);            
        Console.WriteLine("Path = " + pathEnv);
        if(pathEnv.Length > 0)
        {
            Console.WriteLine("Individual Path = " + pathEnv);
        }
        else
        {
            Console.WriteLine("Skipping blank environment path details " +
                    " as it causes exceptions...");
        }
        Console.WriteLine( );
    }
}

If the PATH environment variable contains the following:

PATH=Path=C:\WINDOWS\system32;C:\WINDOWS

then the output of the ParsePathEnvironmentVariable method is as follows:

Path = C:\WINDOWS\system32
GetDirectoryName = C:\WINDOWS
GetExtension =
GetFileName = system32
GetFileNameWithoutExtension = system32
GetFullPath = C:\WINDOWS\system32
GetPathRoot = C:\
HasExtension = False
IsPathRooted = True

Path = C:\WINDOWS
GetDirectoryName = C:\
GetExtension =
GetFileName = WINDOWS
GetFileNameWithoutExtension = WINDOWS
GetFullPath = C:\WINDOWS
GetPathRoot = C:\
HasExtension = False
IsPathRooted = True

Discussion

When working with environment variables in particular, there are a number of cases in which several paths may be concatenated together and you need to parse each one individually. To distinguish each individual path from the others, Microsoft Windows uses the semicolon character. (Other operating systems might use a different character; Unix, Linux, and Mac OS X use a colon.) To make sure that we always use the correct path separation character, the Path class contains a public static field called PathSeparator. This field contains the character used to separate paths in the current platform. This field is marked as read-only, so it cannot be modified.

To obtain each individual path contained in a single string, use the Split instance method from the String class. This method accepts a param array of character values that are used to break apart the string instance. These individual strings containing the paths are returned in a string array. We can then simply use the foreach loop construct to iterate over each string in this string array, and we can use the various static methods of the Path class to operate on each individual path string.

See Also

See the "Path Class" and "Environment Class" topics in the MSDN documentation.