Question

My goal is to match the first 0 and everything after that zero in a decimal value. If the first decimal place is a zero then I want to match the decimal too. If there is no decimal then capture nothing.

Here are some examples of what I want:

180.570123 // should capture the "0123" on the end
180.570    // should capture the "0" on the end
180.0123   // should capture the ".0123" on the end
180.0      // should capture the ".0" on the end
180123     // should capture nothing
180        // should capture nothing

If the first decimal place is a 0 then making the match is easy:

(\.0.*)

My problem is matching when the first decimal place is not a 0. I believe positive lookbehind will fix this issue, but I am not able to get it to work correctly. Here is one regex I have tried:

(?<=^.*\..*)0.*

This regex will eventually be used in Java.

UPDATE:

I am going to use this regex to get rid of numbers and possibly a decimal point on the end of a string using Java’s replaceAll method. I will do this by replacing the capture group with an empty string. Here is a better example of what I want.

String case1 = "180.570123";
String case2 = "180.570";
String case3 = "180.0123";
String case4 = "180.0";
String case5 = "180123";
String case6 = "180";

String result = null;

result = case1.replaceAll( "THE REGEX I NEED", "" );
System.out.println( result ); // should print 180.57

result = case2.replaceAll( "THE REGEX I NEED", "" );
System.out.println( result ); // should print 180.57

result = case3.replaceAll( "THE REGEX I NEED", "" );
System.out.println( result ); // should print 180

result = case4.replaceAll( "THE REGEX I NEED", "" );
System.out.println( result ); // should print 180

result = case5.replaceAll( "THE REGEX I NEED", "" );
System.out.println( result ); // should print 180123

result = case6.replaceAll( "THE REGEX I NEED", "" );
System.out.println( result ); // should print 180

Also, I am testing these regexs at http://gskinner.com/RegExr/

Answer 1

You can use this expression:

\.[1-9]*(0\d*)

And what you want will be in the first capturing group. (Except the decimal point.)

If you want to capture the decimal point too, you can use:

(?:\.[1-9]+|(?=\.))(\.?0\d*)

Example (online):

Pattern p = Pattern.compile("(?:\\.[1-9]+|(?=\\.))(\\.?0\\d*)");

String[] strs = {"180.570123", "180.570", "180.0123", "180.0", "180123", "180", "180.2030405"};

for (String s : strs) {
    Matcher m = p.matcher(s);
    System.out.printf("%-12s: Match: %s%n", s,
        m.find() ? m.group(1) : "n/a");
}

Output:

180.570123  : Match: 0123
180.570     : Match: 0
180.0123    : Match: .0123
180.0       : Match: .0
180123      : Match: n/a
180         : Match: n/a
180.2030405 : Match: 030405