diff --git a/ch12/minigrep/Cargo.lock b/ch12/minigrep/Cargo.lock
new file mode 100644
index 0000000..1ec6ded
--- /dev/null
+++ b/ch12/minigrep/Cargo.lock
@@ -0,0 +1,7 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "minigrep"
+version = "0.1.0"
diff --git a/ch12/minigrep/Cargo.toml b/ch12/minigrep/Cargo.toml
new file mode 100644
index 0000000..64c2a3f
--- /dev/null
+++ b/ch12/minigrep/Cargo.toml
@@ -0,0 +1,6 @@
+[package]
+name = "minigrep"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
diff --git a/ch12/minigrep/output.txt b/ch12/minigrep/output.txt
new file mode 100644
index 0000000..df27091
--- /dev/null
+++ b/ch12/minigrep/output.txt
@@ -0,0 +1,4 @@
+Searching for to
+In file poem.txt
+Are you nobody, too?
+How dreary to be somebody!
diff --git a/ch12/minigrep/poem.txt b/ch12/minigrep/poem.txt
new file mode 100644
index 0000000..7aaea3d
--- /dev/null
+++ b/ch12/minigrep/poem.txt
@@ -0,0 +1,10 @@
+I'm nobody! Who are you?
+Are you nobody, too?
+Then there's a pair of us - don't tell!
+They'd banish us, you know.
+
+How dreary to be somebody!
+How public, like a frog
+To tell your name the livelong day
+To an admiring bog!
+
diff --git a/ch12/minigrep/src/lib.rs b/ch12/minigrep/src/lib.rs
new file mode 100644
index 0000000..f1d25b6
--- /dev/null
+++ b/ch12/minigrep/src/lib.rs
@@ -0,0 +1,135 @@
+use std::error::Error;
+use std::{env, fs};
+
+pub struct Config {
+    pub query: String,
+    pub file_path: String,
+    pub ignore_case: bool,
+}
+
+impl Config {
+    fn new(args: &[String]) -> Config {
+        if args.len() < 3 {
+            panic!("not enough arguments");
+        }
+
+        // let query = &args[1];
+        // let file_path = &args[2];
+
+        // (query, file_path)
+        // (&args[1], &args[2])
+
+        // In this case while learning rust, it is okay
+        // to use clone() here while not managing lifetimes
+        // and such.
+        //
+        // For rush, I will absolutely want to mess with
+        // lifetimes and references for speed.
+        // Gonna make this fast af
+        // https://www.youtube.com/watch?v=y-5JFBEoU9c
+        Config {
+            query: args[1].clone(),
+            file_path: args[2].clone(),
+            ignore_case: false,
+        }
+    }
+
+    pub fn build(args: &[String]) -> Result<Config, &'static str> {
+        if args.len() < 3 {
+            return Err("not enough arguments");
+        }
+
+        Ok(Config {
+            query: args[1].clone(),
+            file_path: args[2].clone(),
+            ignore_case: env::var("IGNORE_CASE").is_ok(),
+        })
+    }
+}
+
+pub fn run(config: Config) -> Result<(), Box<dyn Error>> {
+    // Best to group configuration variables such as query, file_path,
+    // and contents into one structure.
+    let contents = fs::read_to_string(config.file_path)?;
+
+    let results = if config.ignore_case {
+        search_case_insensitive(&config.query, &contents)
+    } else {
+        search(&config.query, &contents)
+    };
+
+    for line in search(&config.query, &contents) {
+        println!("{line}");
+    }
+
+    // println!("With text:\n{contents}");
+
+    Ok(())
+}
+
+pub 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
+}
+
+pub fn search_case_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
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn one_result() {
+        let query = "duct";
+        let contents = "\
+Rust
+safe, fast, productive.
+Pick three.";
+
+        assert_eq!(vec!["safe, fast, productive."], search(query, contents));
+    }
+    #[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)
+        );
+    }
+}
diff --git a/ch12/minigrep/src/main.rs b/ch12/minigrep/src/main.rs
new file mode 100644
index 0000000..7d4a8c4
--- /dev/null
+++ b/ch12/minigrep/src/main.rs
@@ -0,0 +1,44 @@
+// Separation of Concerns for Binary Projects
+// From: https://rust-book.cs.brown.edu/ch12-03-improving-error-handling-and-modularity.html#separation-of-concerns-for-binary-projects
+//
+// When main starts getting large:
+// 1) Split program into main.rs file and lib.rs file and move
+//    program's logic to lib.rs
+// 2) As long as your command line parsing logic is small, it can
+//    remain in main.rs
+// 3) When command line parsing logic starts getting complicated,
+//    extract it from main.rs and move to lib.rs
+//
+// Functions that remain in main should be limited to:
+// 1) Calling the command line parsing logic with argument values
+// 2) Setting up any other configuration
+// 3) Calling a run function in lib.rs
+// 4) Handling the error if `run` returns an error
+
+use std::env;
+use std::process;
+
+use minigrep::Config;
+
+fn main() {
+    let args: Vec<String> = env::args().collect();
+    // dbg!(args);
+
+    // let config = Config::new(&args);
+
+    // unwrap_or_else passes an argument to a closure which is an
+    // anonymous function
+    // eprintln!() for output to stdout
+    let config = Config::build(&args).unwrap_or_else(|err| {
+        eprintln!("Problem parsing arguments: {err}");
+        process::exit(1);
+    });
+
+    println!("Searching for {}", config.query);
+    println!("In file {}", config.file_path);
+
+    if let Err(e) = minigrep::run(config) {
+        eprintln!("Application error: {e}");
+        process::exit(1);
+    }
+}