Java Formatted Regular Expression in Bash

Question

I've got a large number of regular expressions to check, that are outputted in the Java/JavaScript RegEx format as shown:

\d{7}|\d{8}
[a-zA-Z]\d{8}
[a-zA-Z]\d{3}-\d{3}-\d{2}-\d{3}\d[0|1]

Seeing as I have a comfort with Bash, but there are little tricks I may never think of, I was wondering if there is a way I can take a test string to evaluate against this specific format of RegEx.

I've tried a number of greps and evaluating with data I know passes through a RegEx tester as such http://www.cyber-reality.com/regexy.html

In using bash RegEx I can evaluate these correctly, however I don't have the ability to change the way my server outputs these strings to a format I know how to evaluate in bash.

Any thoughts?

Tough to do with bash's regex. As a quick test, I'd go with the Gnu grep with the -P option (Perl regexp). However, that only works until you encounter something particular to Java's regexp. @Sir_Athos approach is the only way to handle everything that Java does. — Devon_C_Miller
– Devon_C_Miller, Commented Aug 29, 2013 at 18:05
Yeah certainly, my idea was a little far fetched and I was looking for a quick fix to my problem (which is always a bad idea). I'll go with his solution as it will avoid me writing an interpreter. — signus
– signus, Commented Aug 30, 2013 at 16:04

Sir Athos · Accepted Answer · 2013-08-29 17:58:00Z

1

I'd recommend writing a command line tool that does the checking. You can then call this tool from a bash script.

Using this starting point, here's something that does what you need:

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

public class RegexTestHarness {
    public static void main(String[] args) {
        try{
            Pattern pattern = Pattern.compile(args[1]);
            Matcher matcher = pattern.matcher(args[2]);

            boolean found = false;
            while (matcher.find()) {
                System.out.println(matcher.group() + ", position " + matcher.start() + ":" + matcher.end() + "\n");
                found = true;
            }
            if (!found) {
                System.out.println("\nNo match found.");
                System.exit(1);
            }
        }
        catch (Exception e) {
            System.out.println("\nCaught an exception. Description: " + e.getMessage());
            System.exit(2);
        }
    }
}

To check if there is any match, you can use this script:

#!/bin/bash
if java RegexTestHarness "my_regex" "my_input_string"; then
    echo "Expression matches"
else
    echo "Expression doesn't match"
fi

To check for a particular result, you can capture the output of the command and process it in your script.

answered Aug 29, 2013 at 17:58

Sir Athos

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1 Comment

signus Over a year ago

Thanks. I'll go with a similar approach. I was trying a fairly farfetched idea and made it more simple in my mind than it really is. Thanks!

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