Feat: Add custom error message.

src/main.rs

@@ -7,14 +7,22 @@ struct Cli {
     path: std::path::PathBuf,
 }
 
-fn main() {
+#[derive(Debug)]
+struct CustomError(String);
+
+fn main() -> Result<(), CustomError> {
     let args = Cli::parse();
 
-    let content = std::fs::read_to_string(&args.path).expect("Could not read file.");
+    // let content = std::fs::read_to_string(&args.path).expect("Could not read file.");
+
+    let content = std::fs::read_to_string(&args.path)
+        .map_err(|err| CustomError(format!("Error reading `{}`: {}", args.path.display(), err)))?;
 
     for line in content.lines() {
         if line.contains(&args.pattern) {
             println!("{}", line)
         }
     }
+
+    Ok(())
 }