Ggtcf

Using JAVA.
I am trying to find a more elegant way for validating a Linux folder path (not including the file name).

What I have so far is this: "^\/$|^((\/([a-zA-Z0-9_-]+))+)$"

Folder paths should include only following characters: letters, numbers, dashes or underscore.

Test cases

Valid/ matches:

• /


• /abc


• /abc/abc/abc/abc

Invalid / not-matches:

• 
  null or empty string
  


• /abc/


• /abc/abc/abc/abc/

Issue with your RegEx

Your supplied RegEx is working on the test-cases.

You could even reduce it by removing backslashes \ and outer pair of parentheses. Begin ^ and end $ are only needed once (around the two alternatives).

Possible Solution using Regular Expression

You can test the RegEx on RegexPlanet.com (click on Java-Button for tests)

^/|(/[a-zA-Z0-9_-]+)+$

or equivalent (see demo on RegexPlanet)

^/|(/[w-]+)+$

Explained:
w matches a word-character (same as [a-zA-Z0-9_], not matching the dash).

Implementation in Java code:

public boolean isValidLinuxDirectory(String path) (/[a-zA-Z0-9_-]+)+$");
 return path != null && !path.trim().isEmpty() && linuxDirectoryPattern.matcher( path ).matches();

Alternative Solution using File

Note the docs on isDirectory():

Returns:
true if and only if the file denoted by this abstract pathname exists and is a directory; false otherwise

So it may only validate your requirements (valid Linux folder) if run on a Linux machine and if the folder/directory exists.

public boolean isValidExistingDirectory(String path) 
 if (path == null 

Extended Solution

As stated in comment the special form of root // should also be valid. Then use this RegEx:

^/|//|(/[w-]+)+$

It supports:

1. root-directory /
   


2. special form of root-directory //
   


3. any non-root directory, which name is composed out of alphas, numbers, dash or underscore (e.g. /abc/123/_abc-123)

See also

• What is the most correct regular expression for a UNIX file path?


• Regular expression to validate windows and linux path with extension


• what is path //, how is it different from /

To cover all cases including the root directory, you will need the following:

^/$|(/[a-zA-Z_0-9-]+)+$

See Regex Demo using global and multiline modifiers.

Here ya go:
/[a-zA-Z0-9_/-]*[^/]$

EDIT

First character matches a forward slash /. The following character group matches a-z, A-Z, 0-9, underscores, forward slashes, and dashes (all accepted directory and filename characters). The following asterisk makes the pattern match that character group 0 or more times (so any combo of those characters). The last character group has a negation ^ meaning it matches anything EXCEPT what's in the character group, being the final forward slash that we don't want to match. Finally the $ to end the string.