Grep Clone

A command-line tool for searching files with pattern matching.

Full source: grep_clone.rk

Key Concepts Demonstrated

• CLI argument parsing
• File I/O with error handling
• String operations (split, contains, trim)
• Resource cleanup with ensure
• Pattern matching with enums

Highlights

Resource Management

func search_file(path: string, pattern: string) -> () or IoError {
    const file = try fs.open(path)
    ensure file.close()  // Guaranteed cleanup

    for line in file.lines() {
        if line.contains(pattern): println(line)
    }
}

The ensure keyword guarantees file.close() runs even on early returns or errors.

Error Handling

enum GrepError {
    NoPattern,
    NoFiles,
    FileError(string),
}

func parse_args(args: Vec<string>) -> Options or GrepError {
    // Returns Result type, caller must handle errors
}

String Processing

for line in file.lines() {
    if case_insensitive {
        if line.to_lowercase().contains(pattern.to_lowercase()) {
            println(line)
        }
    } else {
        if line.contains(pattern) {
            println(line)
        }
    }
}

Running It

rask grep_clone.rk "pattern" file1.txt file2.txt
rask grep_clone.rk -i "case-insensitive" *.txt

What You’ll Learn

• How to parse command-line arguments in Rask
• Error handling patterns with Result types
• Resource management with ensure
• String manipulation and iteration

View full source →