diff --git a/src/lib.rs b/src/lib.rs
index be28858..1901b3d 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,27 +1,56 @@
-use std::fs::File;
-use std::io::prelude::*;
+use std::fs;
+//use std::fs::File;
+//use std::io::prelude::*;
 use std::error::Error;
+use std::env;
 
 pub struct Config {
     query: String,
     filename: String,
+    insensitive: bool,
 }
 
-pub fn run(conf: Config) -> Result<(), Box<Error>> {
-    println!("{:?} {:?}", conf.query, conf.filename);
+pub fn run(conf: Config) -> Result<(), Box<dyn Error>> {
+    let contents = fs::read_to_string(conf.filename)?;
 
-    let mut f = File::open(&conf.filename)?;
+    let results = if conf.insensitive {
+        search(&conf.query, &contents)
+    } else {
+        search_insensitive(&conf.query, &contents)
+    };
 
-    let mut contents = String::new();
-    f.read_to_string(&mut contents)?;
-
-    println!("Searching for '{}'", conf.query);
-    println!("In file '{}'", conf.filename);
-    println!("With text:\n{}", contents);
+    for line in results {
+        println!("{}", line);
+    }
 
     Ok(())
 }
 
+fn search<'a>(query: &str, contents: &'a str) -> Vec<&'a str> {
+    let mut results = Vec::new();
+
+    for line in contents.lines() {
+        if line.contains(query) {
+          results.push(line);
+        }
+    }
+
+    results
+}
+
+fn search_insensitive<'a>(query: &str, contents: &'a str) -> Vec<&'a str> {
+    let query = query.to_lowercase();
+    let mut results = Vec::new();
+
+    for line in contents.lines() {
+        if line.to_lowercase().contains(&query) {
+          results.push(line);
+        }
+    }
+
+    results
+}
+
 impl Config {
     pub fn new(args: &[String]) -> Result<Config, &'static str> {
         if args.len() < 3 {
@@ -31,6 +60,41 @@ impl Config {
         Ok(Config {
             query: args[1].clone(),
             filename: args[2].clone(),
+            insensitive: env::var("CASE_INSENSITIVE").is_err(),
         })
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn case_sensitive() {
+        let query = "duct";
+        let contents = "\
+Rust:
+safe, fast, productive.
+Pick three.";
+
+        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_insensitive(query, contents)
+        );
+    }
+}