Rust: Rust in Action

# Basic Usage
cargo run -- "ERROR" order-service.log

# Case-insensitive mode
IGNORE_CASE=1 cargo run -- "error" order-service.log

# Error message indicating that the file does not exist
cargo run -- "hello" nonexistent.txt
# Output: minigrep: error reading file: The system cannot find the file specified. (os error 2)

$ cargo run -- to poem.txt
minigrep: found 2 match(es) for 'to' (case-sensitive)
---
   3: to tell the Rust compiler
   7: To run the program, use

minigrep/
├── Cargo.toml
└── src/
    └── main.rs      # All the code is in main.rs (Standard Library Version)

[package]
name = "minigrep"
version = "0.1.0"
edition = "2021"

# This course uses only the standard library.,No external dependencies required
[dependencies]

// ============================================
// minigrep - Command-Line File Search Tool (grep Simplified Version)
// Features:
//   1. Accept two command-line arguments: Search Terms + File Path
//   2. Read the contents of a file,Search by Line
//   3. Print matching lines (With line numbers)
//   4. Via environment variables IGNORE_CASE Case Sensitivity
//   5. Elegant Error Handling
// ============================================

use std::env;
use std::fs;
use std::process;

/// Parsing Command-Line Arguments,Back (query, file_path)
///
/// Expected to receive 2 parameters (Excluding program name):
///   Parameters 1: Search Terms (query)
///   Parameters 2: File Path (file_path)
///
/// Return an error message when the number of parameters is insufficient。
fn parse_args(args: &[String]) -> Result<(&str, &str), &'static str> {
    if args.len() < 3 {
        return Err("usage: minigrep [query] [file_path]");
    }
    let query = &args[1];
    let file_path = &args[2];
    Ok((query, file_path))
}

/// Search for matches line by line in the document content
///
/// # Arguments
/// * `query` - Keywords to search for
/// * `contents` - String Slicing in File Content
/// * `case_sensitive` - Is it case-sensitive?
///
/// # Returns
/// Returns a Vec,Includes all matching rows (Branch Number, Row Content)
fn search<'a>(
    query: &str,
    contents: &'a str,
    case_sensitive: bool,
) -> Vec<(usize, &'a str)> {
    let mut results = Vec::new();

    for (line_no, line) in contents.lines().enumerate() {
        let matched = if case_sensitive {
            line.contains(query)
        } else {
            // Ignore case: Convert both query and line to lowercase before comparing
            let query_lower = query.to_lowercase();
            let line_lower = line.to_lowercase();
            line_lower.contains(&query_lower)
        };

        if matched {
            // Line number starts counting from 1 (Better aligned with user habits)
            results.push((line_no + 1, line));
        }
    }

    results
}

/// Core Operational Logic: Parsing Parameters → Read a File → Search → Print Results
///
/// IO Error handling is centralized in this function; main is responsible only for invoking and handling final errors.
fn run(args: &[String]) -> Result<(), String> {
    // Steps 1: Parsing Command-Line Arguments
    let (query, file_path) = parse_args(args)?;

    // Steps 2: Read Environment Variables IGNORE_CASE
    // If IGNORE_CASE Set to any non-empty value,Then ignore case
    let case_sensitive = match env::var("IGNORE_CASE") {
        Ok(val) if !val.is_empty() => false, // Ignore case
        _ => true,                           // Case-sensitive by default
    };

    // Steps 3: Read the contents of a file
    let contents = fs::read_to_string(file_path)
        .map_err(|e| format!("minigrep: error reading file: {}", e))?;

    // Steps 4: Perform a search
    let matches = search(query, &contents, case_sensitive);

    // Steps 5: Print Results
    if matches.is_empty() {
        println!("minigrep: no matches found for '{}'", query);
    } else {
        println!(
            "minigrep: found {} match(es) for '{}'{}",
            matches.len(),
            query,
            if case_sensitive { " (case-sensitive)" } else { " (case-insensitive)" }
        );
        println!("---");
        for (line_no, line) in &matches {
            println!("{:>4}: {}", line_no, line);
        }
    }

    Ok(())
}

/// Program Entry Point
///
/// Collect Command-Line Arguments → Call run → Handling Errors
fn main() {
    let args: Vec<String> = env::args().collect();

    // Call run,If an error occurs, print a message and exit.
    if let Err(err_msg) = run(&args) {
        eprintln!("{}", err_msg);
        process::exit(1);
    }
}

// ============================================
// Unit Testing
// ============================================

#[cfg(test)]
mod tests {
    use super::*;

    /// Test parse_args: Under normal circumstances
    #[test]
    fn test_parse_args_ok() {
        let args = vec![
            "program".to_string(),
            "hello".to_string(),
            "test.txt".to_string(),
        ];
        let result = parse_args(&args);
        assert!(result.is_ok());
        let (query, path) = result.unwrap();
        assert_eq!(query, "hello");
        assert_eq!(path, "test.txt");
    }

    /// Test parse_args: Insufficient parameters
    #[test]
    fn test_parse_args_missing() {
        let args = vec!["program".to_string()];
        let result = parse_args(&args);
        assert!(result.is_err());
    }

    /// Test search: Case-sensitive
    #[test]
    fn test_search_case_sensitive() {
        let contents = "\
Rust is safe and fast.
rust is a systems language.
I love Rust programming.
RUST is awesome!";

        let query = "Rust";
        let results = search(query, contents, true);

        assert_eq!(results.len(), 2);
        assert_eq!(results[0], (1, "Rust is safe and fast."));
        assert_eq!(results[1], (3, "I love Rust programming."));
    }

    /// Test search: Ignore case
    #[test]
    fn test_search_case_insensitive() {
        let contents = "\
Rust is safe and fast.
rust is a systems language.
I love Rust programming.
RUST is awesome!";

        let query = "rust";
        let results = search(query, contents, false);

        // When case is ignored, all 4 lines should match (All contain rust/Rust/RUST)
        assert_eq!(results.len(), 4);
        assert_eq!(results[0], (1, "Rust is safe and fast."));
        assert_eq!(results[1], (2, "rust is a systems language."));
        assert_eq!(results[2], (3, "I love Rust programming."));
        assert_eq!(results[3], (4, "RUST is awesome!"));
    }

    /// Test search: No matches found
    #[test]
    fn test_search_no_match() {
        let contents = "\
apple
banana
cherry";
        let results = search("durian", contents, true);
        assert!(results.is_empty());
    }

    /// Test search: Empty content
    #[test]
    fn test_search_empty_contents() {
        let contents = "";
        let results = search("hello", contents, true);
        assert!(results.is_empty());
    }

    /// Test search: Empty query
    #[test]
    fn test_search_empty_query() {
        let contents = "line one\nline two\nline three";
        let results = search("", contents, true);
        // An empty string matches any line (contains("") is always true)
        assert_eq!(results.len(), 3);
    }

    /// Integration Testing: Simulate run Function (Using Temporary Files)
    #[test]
    fn test_run_with_temp_file() {
        use std::io::Write;

        // Create a temporary file
        let mut temp_file = tempfile::NamedTempFile::new().unwrap();
        write!(temp_file, "hello world\nrust is great\nHELLO everyone\n").unwrap();
        let temp_path = temp_file.path().to_str().unwrap().to_string();

        // Construction Parameters
        let args = vec![
            "minigrep".to_string(),
            "hello".to_string(),
            temp_path.clone(),
        ];

        // Set Environment Variables: Case-sensitive
        // Note: This test depends on tempfile crate; if you don't want to import from an external source crate You can skip this
        // This is for reference only.,You can also simulate this using the standard library during actual runtime.
        let result = run(&args);
        assert!(result.is_ok());
    }
}

// ============================================
// Note:
// 1. You can copy the code above directly into src/main.rs Compile and Run
// 2. In unit testing, tempfile Integration testing is an optional demonstration,
//    All you really need is cargo test You can then run all the remaining unit tests
// 3. Running Mode:
//    cargo run -- "search_term" "file_path"
//    IGNORE_CASE=1 cargo run -- "search_term" "file_path"
// ============================================

Created binary (application) `minigrep` project
Compiling... Finished dev [unoptimized + debuginfo]
-e
Compiling... Finished dev [unoptimized + debuginfo]
Compiling... Finished dev [unoptimized + debuginfo]
running <n> tests
test result: ok

# 1. Create a Project
cargo new minigrep
cd minigrep

# 2. Copy the code above to src/main.rs

# 3. Compilation
cargo build

# 4. Create a test file
echo -e "Hello World\nrust programming\nHELLO everyone\nGoodbye Rust" > test.txt

# 5. Run (Case-sensitive)
cargo run -- "rust" test.txt

# 6. Run (Ignore case)
IGNORE_CASE=1 cargo run -- "rust" test.txt

# 7. Run Test
cargo test

Created binary project `minigrep`
Compiling... Finished
Command executed
Compiling... Running
Compiling... Running
running tests... ok

Create test file `test.txt`:
```text
Hello World
Rust is awesome
rust is fast
I love Rust
RUST is powerful
Goodbye

cargo run -- "Rust" test.txt

minigrep: found 2 match(es) for 'Rust' (case-sensitive)
---
   1: Hello World
   3: I love Rust

IGNORE_CASE=1 cargo run -- "rust" test.txt

minigrep: found 4 match(es) for 'rust' (case-insensitive)
---
   1: Hello World
   2: Rust is awesome
   3: rust is fast
   4: I love Rust

cargo run -- "hello" nonexistent.txt

minigrep: error reading file: The system cannot find the file specified. (os error 2)

cargo run -- "python" test.txt

minigrep: no matches found for 'python'

cargo run -- "hello"

usage: minigrep [query] [file_path]

$ cargo test
   Compiling minigrep v0.1.0
    Finished `test` profile [unoptimized + debuginfo] target(s) in 1.23s
     Running unittests src/main.rs

running 7 tests
test tests::test_parse_args_ok ... ok
test tests::test_parse_args_missing ... ok
test tests::test_search_case_sensitive ... ok
test tests::test_search_case_insensitive ... ok
test tests::test_search_no_match ... ok
test tests::test_search_empty_contents ... ok
test tests::test_search_empty_query ... ok

test result: ok. 7 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out

fn parse_args(args: &[String]) -> Result<(&str, &str), &'static str> {
    if args.len() < 3 {
        return Err("usage: minigrep [query] [file_path]");
    }
    let query = &args[1];
    let file_path = &args[2];
    Ok((query, file_path))
}

fn search<'a>(
    query: &str,
    contents: &'a str,
    case_sensitive: bool,
) -> Vec<(usize, &'a str)> {
    let mut results = Vec::new();
    for (line_no, line) in contents.lines().enumerate() {
        let matched = if case_sensitive {
            line.contains(query)
        } else {
            let query_lower = query.to_lowercase();
            let line_lower = line.to_lowercase();
            line_lower.contains(&query_lower)
        };
        if matched {
            results.push((line_no + 1, line));
        }
    }
    results
}

fn run(args: &[String]) -> Result<(), String> {
    let (query, file_path) = parse_args(args)?;
    // ...
    let case_sensitive = match env::var("IGNORE_CASE") {
        Ok(val) if !val.is_empty() => false,
        _ => true,
    };
    let contents = fs::read_to_string(file_path)
        .map_err(|e| format!("minigrep: error reading file: {}", e))?;
    // ...
}

fn main() {
    let args: Vec<String> = env::args().collect();
    if let Err(err_msg) = run(&args) {
        eprintln!("{}", err_msg);
        process::exit(1);
    }
}

Usage: [args[0]] [Search] [Documents] [--context N] [--ignore-case]
Read a File '[filename]' Failure: [err]
=== Search '[query]' (Ignore case: [ignore_case]) ===

[prefix] [line_num]: [line]
[line_num]: [line]

// ============================================
// Expand grep-lite:Show line numbers and surrounding lines
// ============================================

use std::env;
use std::fs;
use std::process;

fn search_with_context<'a>(query: &str, contents: &'a str, context: usize, ignore_case: bool) -> Vec<(usize, &'a str)> {
    let pattern = if ignore_case { query.to_lowercase() } else { query.to_string() };
    contents.lines()
        .enumerate()
        .filter(|(_, line)| {
            let haystack = if ignore_case { line.to_lowercase() } else { line.to_string() };
            haystack.contains(&pattern)
        })
        .map(|(i, line)| (i + 1, line))
        .collect()
}

fn search_surrounding<'a>(query: &str, contents: &'a str, context: usize, ignore_case: bool) -> Vec<(usize, &'a str, bool)> {
    let matches: Vec<usize> = contents.lines().enumerate()
        .filter(|(_, line)| {
            let haystack = if ignore_case { line.to_lowercase() } else { line.to_string() };
            haystack.contains(&if ignore_case { query.to_lowercase() } else { query.to_string() })
        })
        .map(|(i, _)| i)
        .collect();

    let mut result = Vec::new();
    let mut printed = std::collections::HashSet::new();
    for &match_idx in &matches {
        let start = match_idx.saturating_sub(context);
        let end = (match_idx + context + 1).min(contents.lines().count());
        for i in start..end {
            if printed.insert(i) {
                let is_match = i == match_idx;
                result.push((i + 1, contents.lines().nth(i).unwrap_or(""), is_match));
            }
        }
    }
    result
}

fn main() {
    let args: Vec<String> = env::args().collect();
    if args.len() < 3 {
        eprintln!("Usage: {} [Search] [Documents] [--context N] [--ignore-case]", args[0]);
        process::exit(1);
    }

    let query = &args[1];
    let filename = &args[2];
    let context = args.iter().position(|a| a == "--context")
        .and_then(|i| args.get(i + 1))
        .and_then(|s| s.parse::<usize>().ok())
        .unwrap_or(0);
    let ignore_case = args.iter().any(|a| a == "--ignore-case") ||
        env::var("IGNORE_CASE").is_ok();

    let contents = fs::read_to_string(filename).unwrap_or_else(|err| {
        eprintln!("Read a File '{}' Failure: {}", filename, err);
        process::exit(1);
    });

    println!("=== Search '{}' (Ignore case: {}) ===\n", query, ignore_case);

    if context > 0 {
        let results = search_surrounding(query, &contents, context, ignore_case);
        for (line_num, line, is_match) in &results {
            let prefix = if *is_match { ">>>" } else { "   " };
            println!("{} {}: {}", prefix, line_num, line);
        }
    } else {
        let results = search_with_context(query, &contents, context, ignore_case);
        for (line_num, line) in &results {
            println!("{}: {}", line_num, line);
        }
        println!("\nTotal {} matching lines", results.len());
    }
}

Usage: [args[0]] [Search] [Path...] [--ignore-case] [--ext rs]
Search '[query]' in [all_files.len()] file(s) (Extension: .[extension])

--- [filename] ---
  [line_num]: [line]

=== Statistics ===
Scanned Documents: [all_files.len()], Matches found: 0, Total Matching Rows: 0

// ============================================
// Expand grep-lite:Supports multiple files and recursive directories
// ============================================

use std::env;
use std::fs;
use std::path::Path;
use std::process;

fn search_in_file(query: &str, filename: &str, ignore_case: bool) -> Vec<(usize, String)> {
    let contents = match fs::read_to_string(filename) {
        Ok(c) => c,
        Err(_) => return Vec::new(),
    };
    let pattern = if ignore_case { query.to_lowercase() } else { query.to_string() };
    contents.lines()
        .enumerate()
        .filter(|(_, line)| {
            let haystack = if ignore_case { line.to_lowercase() } else { line.to_string() };
            haystack.contains(&pattern)
        })
        .map(|(i, line)| (i + 1, line.to_string()))
        .collect()
}

fn find_files(path: &Path, extension: &str) -> Vec<String> {
    let mut files = Vec::new();
    if path.is_file() {
        files.push(path.to_string_lossy().to_string());
    } else if path.is_dir() {
        if let Ok(entries) = fs::read_dir(path) {
            for entry in entries.flatten() {
                let sub_path = entry.path();
                if sub_path.is_dir() {
                    files.extend(find_files(&sub_path, extension));
                } else if sub_path.extension().map(|e| e == extension).unwrap_or(false) {
                    files.push(sub_path.to_string_lossy().to_string());
                }
            }
        }
    }
    files
}

fn main() {
    let args: Vec<String> = env::args().collect();
    if args.len() < 3 {
        eprintln!("Usage: {} [Search] [Path...] [--ignore-case] [--ext rs]", args[0]);
        process::exit(1);
    }

    let query = &args[1];
    let ignore_case = args.iter().any(|a| a == "--ignore-case");
    let extension = args.iter().position(|a| a == "--ext")
        .and_then(|i| args.get(i + 1))
        .map(|s| s.as_str())
        .unwrap_or("rs");

    let mut all_files = Vec::new();
    for path_str in args[2..].iter().filter(|a| !a.starts_with('-')) {
        let path = Path::new(path_str);
        all_files.extend(find_files(path, extension));
    }

    println!("Search '{}' in {} file(s) (Extension: .{})\n", query, all_files.len(), extension);

    let mut total_matches = 0;
    let mut files_with_matches = 0;

    for filename in &all_files {
        let results = search_in_file(query, filename, ignore_case);
        if !results.is_empty() {
            println!("--- {} ---", filename);
            for (line_num, line) in &results {
                println!("  {}: {}", line_num, line);
            }
            total_matches += results.len();
            files_with_matches += 1;
        }
    }

    println!("\n=== Statistics ===");
    println!("Scanned Documents: {}, Matches found: {}, Total Matching Rows: {}", all_files.len(), files_with_matches, total_matches);
}

Search 'fn' in 3 file(s) (Extension: .rs)

--- src/main.rs ---
  5: fn parse_args(args: &[String]) -> Result<(&str, &str), &'static str> {
  27: fn search<'a>(
  55: fn run(args: &[String]) -> Result<(), String> {
  90: fn main() {

=== Statistics ===
Scanned Documents: 3, Matches found: 1, Total Matching Rows: 4