Using the java.util.regex package

Question

I am trying to use the regex package to grep out portions of a string that match a regular expression. Some code from my class
    String fileList = "1_tmp.txt 2_tmp.txt 3_tmp.txt 1_inpt.txt 2_inpt.txt 3_inpt.txt 1_out.txt 2_out.txt 3_out.txt";
    String regex = "[0-9].*_out.txt"  ;
    Pattern pat = Pattern.compile(regex);
    Matcher m = pat.matcher(fileList);
    boolean succ = m.find();
    for (int i =0; i< m.groupCount(); i++) {
        System.out.println(m.group(i));
    }I was expecting to see
1_out.txt
2_out.txt
3_out.txt
This doesnt work this way, nothing gets printed out. Anybody has any idea what is wrong here?
I am basically trying to get the same functionality as
ls | grep "*_out.txt"
Also is there any way to do a OR in the regular expression, like
match [0-9]*_out.txt OR [0-9]*_out.txt
Thanks
-kn

Answer 1

I don't see a difference in your OR, but look in the Pattern JavaDocs under logical operators.
Second, groups are not appropriate in your situation. You have a single pattern which you wish to repeatedly find. Groups are used when you wish to pick out one subsection of a matched item. For example, a pattern dealing with a phone number might have three groups, the area code, the prefix, and the rest.
Still, group 0 is by definition the entire matched item, so if your pattern was right, it should have worked.
I think the critical piece is the ".*" section. * is a greedy marker and combined with the 'any chacter' marker will eat as many characters as it can. In this case, it's probably eating the rest of the string, which leaves nothing left for the "_out.txt" part of the pattern. Try using the *?, which is a reluctant marker and will basically look ahead in the pattern and eat the minimum number of characters it can.