Java regex - multiple substitutions

Question

I need to fetch hostname from a fully qualified domain name String. All parental domain / subdomain / interface names should be stripped, i.e.

abc001 -> abc001     ## stays name ##
efg.fqdn.com -> efg  ## only 1st/short name ##
mnop-int -> mnop     ## only 1st/short name ##
help-adm.fqdn -> help  ## only 1st/short name ##

I've tried various combinations similar to this:

(.*?)(?:.|-)

but it didn't help much.

PS: The regex should be a single-liner, as it is goes as an input in application.

don't you think help-adm and mnop-int should be part of answer. i.e. mnop-int.subdomain.domin — Manoj
– Manoj, Commented Oct 19, 2015 at 12:59
@Manoj, not exactly...if the server is resolvable by a different interface, such as server-int or server-adm we have to remove the '-int' or '-adm' from it's name. — Marcos
– Marcos, Commented Oct 19, 2015 at 13:31

Tunaki · Accepted Answer · 2015-10-19 11:56:59Z

1

If I understand your requirement right, you want to get the part of a String before the first dot or hyphen.

In this case, the following regex will work: "([^.-]*)[.-]?". The first match will be the desired String.

Test code:

public static void main(String[] args) throws Exception {
    String[] strs = { "abc001", "efg.fqdn.com", "mnop-int", "help-adm.fqdn" };
    Pattern pattern = Pattern.compile("([^.-]*)[.-]?");
    for (String str : strs) {
        Matcher matcher = pattern.matcher(str);
        if (matcher.find()) {
            System.out.println(matcher.group(1));
        }
    }
}

Output:

abc001
efg
mnop
help

answered Oct 19, 2015 at 11:56

Tunaki

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2 Comments

Marcos Over a year ago

yes your understanding is correct, but when I run the regex, it's showing all separated values as output, instead of just the first separated value..

Tunaki Over a year ago

@Marcos I just re-ran the sample code in my answer and this works fine.

Manoj · Accepted Answer · 2015-10-19 12:42:45Z

1

Regex flavor other than Java-

^.*?\\b

You can \b or word boundary here.See demo.

https://regex101.com/r/tD0dU9/3

word boundary \b won't work in this case as Java includes all unicode characters range as a word boundary condition.

edited Oct 19, 2015 at 12:42

Manoj

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answered Oct 19, 2015 at 11:47

vks

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Comments

Manoj · Accepted Answer · 2015-10-19 12:44:35Z

0

As Java's \b boundary condition is little bit different than other regular expression engine, We need to take more care when we are using boundary conditions.

public class BoundaryCondRegEx {

 public static void main(String[] args) {

    Pattern p = Pattern.compile("^(?<n>\\w+).*$");
    Matcher m = p.matcher("mnop-int");
    if(m.matches())
    {
        System.out.print(m.group("n"));
    }
    else
        System.out.println("Nope");

   }

}

So As mentioned in pattern "^(?<n>\\w+).*$"
\w is representing [0-9A-Za-z_]
if your resultant substring is made of these chars, you are fine.

answered Oct 19, 2015 at 12:44

Manoj

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