How to find whether a given path is absolute/relative and convert it to absolute for file manipulation?

Question

I am writing a small windows script in javascript/jscript for finding a match for a regexp with a string that i got by manipulating a file.

The file path can be provided relative or absolute. How to find whether a given path is absolute/relative and convert it to absolute for file manipulation?

Answer 1

To check whether the path is relative or absolute, look for a leading /. If it doesn't have one, you need to concatenate the path to a base path. Some programming environments have a "current working directory", but Javascript that lives in the browser doesn't, so you just need to pick a base path and stick to it.

function full_path(my_path) {
    var base_path = "/home/Sriram/htdocs/media";
    var path_regex = /^\/.*$/;
    if(path_regex.test(my_path)) {
        return my_path;
    } else {
        return base_path + my_path;
    }
}

Paths can contain newlines, which the javascript regex . won't match, so you might want to develop a more sophisticated regex to make sure all paths will work properly. However, I'd consider that outside the scope of this answer, and of my knowledge. :-)

Answer 2

How to find whether a given path is absolute/relative ...

From the MSDN article Naming Files, Paths, and Namespaces:

A file name is relative to the current directory if it does not begin with one of the following:

• A UNC name of any format, which always start with two backslash characters ("\\"). For more information, see the next section.
• A disk designator with a backslash, for example "C:\" or "d:\".
• A single backslash, for example, "\directory" or "\file.txt". This is also referred to as an absolute path.

So, strictly speaking, an absolute path is the one that begins with a single backslash (\). You can check this condition as follows:

if (/^\\(?!\\)/.test(path)) {
  // path is absolute
}
else {
  // path isn't absolute
}

But often by an absolute path we actually mean a fully qualified path. In this is the case, you need to check all three conditions in order to distinguish between full and relative paths. For example, your code could look like this:

function pathIsAbsolute(path)
{
  if ( /^[A-Za-z]:\\/.test(path) ) return true;
  if ( path.indexOf("\\") == 0 )   return true;
  return false;
}

or (using a single regex and a bit less readable):

function pathIsAbsolute(path)
{
  return /^(?:[A-Za-z]:)?\\/.test(path);
}

---

... and convert it to absolute for file manipulation?

Use the FileSystemObject.GetAbsolutePathName method:

var fso = new ActiveXObject("Scripting.FileSystemObject");
var full_path = fso.GetAbsolutePathName(path);