Java regex for Windows file path

Question

I'm trying to build a Java regex to search a .txt file for a Windows formatted file path, however, due to the file path containing literal backslashes, my regex is failing.

The .txt file contains the line:

C\Windows\SysWOW64\ntdll.dll

However, some of the filenames in the text file are formatted like this:

C\Windows\SysWOW64\ntdll.dll (some developer stuff here...)

So I'm unable to use String.equals

To match this line, I'm using the regex:

filename = "C\\Windows\\SysWOW64\\ntdll.dll"
read = BufferedReader.readLine();

if (Pattern.compile(Pattern.quote(filename), Pattern.CASE_INSENSITIVE).matcher(read).find()) {

I've tried escaping the literal backslashes, using the replace method, i.e:

filename.replace("\\", "\\\\");

However, this is failing to find, I'm guessing this is because I need to further escape the backslashes after the Pattern has been built, I'm thinking I might need to escape upto an additional four backslashes, i.e:

Pattern.replaceAll("\\\\", "\\\\\\\\");

However, each time I try, the pattern doesn't get matched. I'm certain it's a problem with the backslashes, but I'm not sure where to do the replacement, or if there's a better way of building the pattern.

I think the problem is further being compounded as the replaceAll method also uses a regex, with means the pattern will have it's own backslashes in there, to deal with the case insensitivity.

Any input or advice would be appreciated.

Thanks

Answer 1

Seems like you're attempting to to a direct comparison of String against another. For exact matches, you could do (

if (read.equalsIgnoreCase(filename)) {

of simply

if (read.startsWith(filename)) {

Answer 2

Try this :

While reading each line from the file, replace '\' by '\\'.

Then :

String lLine = "C\\Windows\\SysWOW64\\ntdll.dll";
Pattern lPattern = Pattern.compile("C\\\\Windows\\\\SysWOW64\\\\ntdll\\.dll");
Matcher lMatcher = lPattern.matcher(lLine);
if(lMatcher.find()) {
    System.out.println(lMatcher.group());
}

lLine = "C\\Windows\\SysWOW64\\ntdll.dll (some developer stuff here...)";
lMatcher = lPattern.matcher(lLine);
if(lMatcher.find()) {
    System.out.println(lMatcher.group());
}

Answer 3

The correct usage will be:

String filename = "C\\Windows\\SysWOW64\\ntdll.dll";
String file = filename.replace('\\', ' ');