Read regular expression from console : Introduction « Regular Expressions « Java Tutorial

1. Java Tutorial
2. Regular Expressions
3. Introduction

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import java.io.Console;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
import java.util.regex.PatternSyntaxException;

public class RegexTestHarness2 {

  public static void main(String[] args) {
    Pattern pattern = null;
    Matcher matcher = null;

    Console console = System.console();
    if (console == null) {
      System.err.println("No console.");
      System.exit(1);
    }
    while (true) {
      try {
        pattern = Pattern.compile(console.readLine("%nEnter your regex: "));

        matcher = pattern.matcher(console
            .readLine("Enter input string to search: "));
      } catch (PatternSyntaxException pse) {
        console.format("There is a problem with the regular expression!%n");
        console.format("The pattern in question is: %s%n", pse.getPattern());
        console.format("The description is: %s%n", pse.getDescription());
        console.format("The message is: %s%n", pse.getMessage());
        console.format("The index is: %s%n", pse.getIndex());
        System.exit(0);
      }
      boolean found = false;
      while (matcher.find()) {
        console.format("I found the text \"%s\" starting at "
            + "index %d and ending at index %d.%n", matcher.group(), matcher
            .start(), matcher.end());
        found = true;
      }
      if (!found) {
        console.format("No match found.%n");
      }
    }
  }
}