Rust Text Search Tool Tutorial | Find Patterns with Line Numbers | Rust by Examples #9

Rust Text Search Tool Tutorial | Find Patterns with Line Numbers

In this tutorial, you'll learn how to build a simple text search tool in Rust that reads a file, searches for a pattern case-insensitively, and displays matching lines along with their line numbers. The example demonstrates using Rust's powerful iterator methods for clean and concise code.

Code

use std::fs;

// Struct to hold each search result with line number and content
struct SearchResult {
  line_number: usize,
  line: String,
}

// Search function: finds all lines containing the pattern (case-insensitive)
fn search(content: &str, pattern: &str) -> Vec<SearchResult> {
  let pattern = pattern.to_lowercase();

  content
    .lines()
    .enumerate() // adds line numbers starting at 0
    .filter_map(|(idx, line)| {
      // Check if line contains pattern (case-insensitive)
      if line.to_lowercase().contains(&pattern) {
        Some(SearchResult {
          line_number: idx + 1, // line numbers start at 1
          line: line.to_string(),
        })
      } else {
        None
      }
    })
    .collect()
}

fn main() {
  // Read the entire file into a string
  let content = fs::read_to_string("sample.txt").expect("Failed to read file");

  let pattern = "rust";

  // Perform the search
  let results = search(&content, pattern);

  println!("Found {} matches for '{}':", results.len(), pattern);

  // Display each matching line with its line number
  for result in results {
    println!("{}: {}", result.line_number, result.line);
  }
}

Key Points

• Use fs::read_to_string to read an entire file into a string for processing.
• Split text into lines with lines() and pair lines with their indices using enumerate().
• Perform case-insensitive searches by converting both the pattern and lines to lowercase before matching.
• Use iterator adapters like filter_map() to filter and transform lines that match the search pattern.
• Collect matching results into a vector of structs to keep track of line numbers and content for easy display.