This is a starting point for Go solutions to the "Build Your Own grep" Challenge.

Regular expressions (Regexes, for short) are patterns used to match character combinations in strings. grep is a CLI tool for searching using Regexes.

In this challenge you'll build your own implementation of grep. Along the way we'll learn about Regex syntax, how parsers/lexers work, and how regular expressions are evaluated.

Note: If you're viewing this repo on GitHub, head over to codecrafters.io to try the challenge.

Passing the first stage

The entry point for your grep implementation is in cmd/mygrep/main.go. Study and uncomment the relevant code, and push your changes to pass the first stage:

git add .
git commit -m "pass 1st stage" # any msg
git push origin master

Time to move on to the next stage!

Stage 2 & beyond

Note: This section is for stages 2 and beyond.

1. Ensure you have go (1.19) installed locally
2. Run ./your_program.sh to run your program, which is implemented in cmd/mygrep/main.go.
3. Commit your changes and run git push origin master to submit your solution to CodeCrafters. Test output will be streamed to your terminal.
4. C Implementation Reference

    /* match: search for regexp anywhere in text */
    int match(char *regexp, char *text)
    {
        if (regexp[0] == '^')
            return matchhere(regexp+1, text);
        do {    /* must look even if string is empty */
            if (matchhere(regexp, text))
                return 1;
        } while (*text++ != '\0');
        return 0;
    }

    /* matchhere: search for regexp at beginning of text */
    int matchhere(char *regexp, char *text)
    {
        if (regexp[0] == '\0')
            return 1;
        if (regexp[1] == '*')
            return matchstar(regexp[0], regexp+2, text);
        if (regexp[0] == '$' && regexp[1] == '\0')
            return *text == '\0';
        if (*text!='\0' && (regexp[0]=='.' || regexp[0]==*text))
            return matchhere(regexp+1, text+1);
        return 0;
    }

    /* matchstar: search for c*regexp at beginning of text */
    int matchstar(int c, char *regexp, char *text)
    {
        do {    /* a * matches zero or more instances */
            if (matchhere(regexp, text))
                return 1;
        } while (*text != '\0' && (*text++ == c || c == '.'));
        return 0;
    }