Tag: RegExp

Capturing groups using regular expressions (RegEx) in JavaScript

Posted: 2007-11-26   |   Categories: JavaScript, Programming   |   Tags: RegExp

There are whole books about regular expressions so this post shouldn’t be intended as an exhaustive resource on the subject. It just shows how to extract a substring from a string using regular expressions in JavaScript so it must be considered just a tip not a tutorial on RegExp. Look at the following example:

    
var str = "https://www.alessandrolacava.com/?code=ALE69";
var regex = /code=(w+)&?/;
var results = regex.exec(str);
if(!results){
  alert("no match");
}
else{
  // first group
  alert(results[1]);
}

The previous code extracts the string that follows the code= part of str. That string is captured in the first group. of the RegExp, that’s why I use results[1] to display it. When you utilise groups–through the use of parenthesis ()–you can refer to them using indices, starting from 1. Indeed, at the index 0 you find the whole match. In the previous example, results[0] is equal to code=ALE69

How to select any character across multiple lines in Java

Posted: 2006-10-10   |   Categories: Java, Programming   |   Tags: RegExp

You can do that using the following pattern in the compile static method of the java.util.regex.Pattern class. The pattern is (.|n|r)*? which means: any character (the .) or (the |) n or r. Zero or more times (the *) of the whole stuff.

Example: The following method strips the multiline comments (those between /* and */) from a string passed in and returns the resulting string:

 
import java.util.regex;

// ... other code 

// Strip multiline comments
public void deleteMultilineComments(String subject) {
  Pattern pattern = Pattern.compile("(/\\*(.|n|r)*?\\*/)");
  Matcher matcher = pattern.matcher(subject);
  return matcher.replaceAll("");
}

Note: rn works for Windows systems. n works for Unix-like systems. r works for Mac systems.

How to force one or more metacharacters to be treated as ordinary characters in a Java Regular Expression (RegEx)

Posted: 2006-07-12   |   Categories: Java, Programming   |   Tags: Metacharacter, RegExp

When using RegEx in Java you might face the need of treating one or more metacharacters as ordinary characters. As a reminder the metacharacters in a Java RegEx are:

([{^$|)?*+.

If you want to treat them as ordinary characters you have two options:

1. Escape the metacharacter with a backslash,
2. Enclose the whole string that contains metacharacters within Q and E

Q means: “quotes all characters until E”, while E ends the quotes.