diff --git a/output.txt b/output.txt
new file mode 100644
index 0000000..7028ba1
--- /dev/null
+++ b/output.txt
@@ -0,0 +1,5 @@
+Searching for to
+In file poem.txt
+Found!
+Are you nobody, too?
+How dreary to be somebody!
diff --git a/src/lib.rs b/src/lib.rs
index 19e8e50..dfb9722 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,4 +1,53 @@
-//TODO implement search function
-pub fn search() {
-    unimplemented!();
+/*
+    contents: "Shall I compare thee\nto a summer's day"
+                 ↑
+    Vec[0]:  &"Shall I compare thee"   ← punta qui dentro, non è una copia
+*/
+pub fn search_case_insensitive<'a>(query: &str, contents: &'a str) -> Vec<&'a str> {
+    let query = query.to_lowercase();
+    let results = contents
+        .lines() // lines gives slice that points to memory of contents
+        .filter(|line| line.to_lowercase().contains(&query))
+        .collect();
+
+    results
+}
+
+pub fn search<'a>(query: &str, contents: &'a str) -> Vec<&'a str> {
+    contents
+        .lines() // lines gives slice that points to memory of contents
+        .filter(|line| line.contains(query))
+        .collect()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn case_sensitive() {
+        let query = "duct";
+        let contents = "\
+Rust:
+safe, fast, productive.
+Pick three.
+Duct tape.";
+
+        assert_eq!(vec!["safe, fast, productive."], search(query, contents));
+    }
+
+    #[test]
+    fn case_insensitive() {
+        let query = "rUsT";
+        let contents = "\
+Rust:
+safe, fast, productive.
+Pick three.
+Trust me.";
+
+        assert_eq!(
+            vec!["Rust:", "Trust me."],
+            search_case_insensitive(query, contents)
+        );
+    }
 }
\ No newline at end of file
diff --git a/src/main.rs b/src/main.rs
index 6fc4d3e..852990a 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -3,7 +3,7 @@ use std::env;
 use std::error::Error;
 use std::process;
 
-use minigrep::search;
+use minigrep::{search, search_case_insensitive};
 
 
 fn main() -> Result<(), Box<dyn Error>> {
@@ -16,7 +16,7 @@ fn main() -> Result<(), Box<dyn Error>> {
     // let config = Config::build(&args)?;
     // or
     let config = Config::build(&args).unwrap_or_else(|err| {
-        println!("Problem parsing arguments: {err}");
+        eprintln!("Problem parsing arguments: {err}");
         process::exit(1);
     });
 
@@ -26,7 +26,7 @@ fn main() -> Result<(), Box<dyn Error>> {
     // run(config)?;
     // or
     if let Err(e) = run(config) {
-        println!("Application error: {e}");
+        eprintln!("Application error: {e}");
         process::exit(1);
     }
     
@@ -35,16 +35,24 @@ fn main() -> Result<(), Box<dyn Error>> {
 
 fn run (config: Config) -> Result<(), Box<dyn Error>> {
     let contents: String = fs::read_to_string(config.file_path)?;
-    println!("With text:\n{contents}");
 
-    search();
+    // results can't be used after contents die
+    let results = if config.ignore_case {
+        search_case_insensitive(&config.query, &contents)
+    } else {
+        search(&config.query, &contents)
+    };
+
+    println!("Found!");
+    for line in results { println!("{line}"); }   
 
     Ok(())
 }
 
 struct Config {
-    query: String,
-    file_path: String,
+    pub query: String,
+    pub file_path: String,
+    pub ignore_case: bool,
 }
 
 impl Config {
@@ -58,7 +66,9 @@ impl Config {
         let query = args[1].clone();
         let file_path = args[2].clone();
 
-        Ok(Config { query, file_path })
+        let ignore_case = env::var("IGNORE_CASE").is_ok();
+
+        Ok(Config { query, file_path, ignore_case })
     }
 }