Question

I am trying to get a regular expression to find multiple entries of my pattern on a line. Note: I’ve been using Regex for about an hour… =/

For example:

<a href="G2532" id="1">back</a> <a href="G2564" id="2">next</a>

Should match twice:

1) <a href="G2532" id="1">back</a>
2) <a href="G2564" id="2">next</a>

I think the answer lies in the proper mastery of greedy vs reluctant vs possessive but I can’t seem to get it to work…

I think I am close, the Regex string I have created so far is:

(<a href=").*(" id="1">).*(</a>)

But the Regex matcher returns 1 match, the entire string…

I have a (compilable) Java Regex Test Harness in code below. Here’s my recent (futile) attempts to get this using that program, the output should be pretty intuitive.

Enter your regex: (<a href=").*(" id="1">).*(</a>)
Enter input string to search: <a href="G2532" id="1">back</a> <a href="G2564" id="2">next</a>
I found the text "<a href="G2532" id="1">back</a> <a href="G2564" id="2">next</a>" starting at index 0 and ending at index 63.

Enter your regex: (<a href=").*(" id="1">).*(</a>)?
Enter input string to search: <a href="G2532" id="1">back</a> <a href="G2564" id="2">next</a>
I found the text "<a href="G2532" id="1">back</a> <a href="G2564" id="2">next</a>" starting at index 0 and ending at index 63.

Enter your regex: (<a href=").*(" id="1">).*(</a>)+
Enter input string to search: <a href="G2532" id="1">back</a> <a href="G2564" id="2">next</a>
I found the text "<a href="G2532" id="1">back</a> <a href="G2564" id="2">next</a>" starting at index 0 and ending at index 63.

Enter your regex: (<a href=").*(" id="1">).*(</a>)?
Enter input string to search: <a href="G2532" id="1">back</a> <a href="G2564" id="2">next</a>
I found the text "<a href="G2532" id="1">back</a> <a href="G2564" id="2">next</a>" starting at index 0 and ending at index 63.

Enter your regex: ((<a href=").*(" id="1">).*(</a>))?
Enter input string to search: <a href="G2532" id="1">back</a> <a href="G2564" id="2">next</a>
I found the text "<a href="G2532" id="1">back</a> <a href="G2564" id="2">next</a>" starting at index 0 and ending at index 63.
I found the text "" starting at index 63 and ending at index 63.

Enter your regex: ((<a href=").*(" id="1">).*(</a>))+?
Enter input string to search: <a href="G2532" id="1">back</a> <a href="G2564" id="2">next</a>
I found the text "<a href="G2532" id="1">back</a> <a href="G2564" id="2">next</a>" starting at index 0 and ending at index 63.

Enter your regex: (((<a href=").*(" id="1">).*(</a>))+?)
Enter input string to search: <a href="G2532" id="1">back</a> <a href="G2564" id="2">next</a>
I found the text "<a href="G2532" id="1">back</a> <a href="G2564" id="2">next</a>" starting at index 0 and ending at index 63.

Here’s the Java:

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.regex.Pattern;
import java.util.regex.Matcher;

public class RegexTestHarness {

    public static void main(String[] args){
        try{
            while (true) {

                System.out.print("\nEnter your regex: ");

                BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
                Pattern pattern = Pattern.compile(reader.readLine());

                System.out.print("Enter input string to search: ");
                Matcher matcher = pattern.matcher(reader.readLine());

                boolean found = false;
                while (matcher.find()) {
                    System.out.println("I found the text \"" + matcher.group() + "\" starting at " +
                       "index " + matcher.start() + " and ending at index " + matcher.end() + ".");
                    found = true;
                }
                if(!found){
                    System.out.println("No match found.");
                }
            }
        } catch (IOException e) {
            e.printStackTrace();
            System.exit(-1);
        }

    }
}

Answer 1

Try this:

<a href=".*?" id="1">.*?</a>

I’ve converted the captures to non-greedy by adding a ? after .*

But when in doubt, you can use this trick:

<a href="[^"]*" id="1">[^<]*</a>

[^"]* means any number of characters that aren’t a double quote
[^<]* means any number of characters that aren’t a left angle

So you avoid worrying about greedy/non-greedy