// strings/JGrep.java

// (c)2021 MindView LLC: see Copyright.txt

// We make no guarantees that this code is fit for any purpose.

// Visit http://OnJava8.com for more book information.

// A very simple version of the "grep" program

// {java JGrep

// WhitherStringBuilder.java "return|for|String"}

import java.util.regex.*;

import java.nio.file.*;

import java.util.stream.*;

public class JGrep {

public static void

main(String[] args) throws Exception {

if(args.length < 2) {

System.out.println(

"Usage: java JGrep file regex");

System.exit(0);

}

Pattern p = Pattern.compile(args[1]);

Matcher m = p.matcher("");

// Iterate through the lines of the input file:

Files.readAllLines(Paths.get(args[0])).forEach(

line -> {

m.reset(line);

while(m.find())

System.out.println(

m.group() + ": " + m.start());

}

);

}

}

/* Output:

String: 18

String: 20

String: 9

String: 25

String: 4

for: 4

String: 8

return: 4

String: 9

String: 25

String: 4

String: 31

for: 4

String: 8

return: 4

String: 20

*/