diff --git a/Cargo.lock b/Cargo.lock
index cba7139..676fe12 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -2,6 +2,21 @@
 # It is not intended for manual editing.
 version = 3
 
+[[package]]
+name = "android-tzdata"
+version = "0.1.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e999941b234f3131b00bc13c22d06e8c5ff726d1b6318ac7eb276997bbb4fef0"
+
+[[package]]
+name = "android_system_properties"
+version = "0.1.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "819e7219dbd41043ac279b19830f2efc897156490d7fd6ea916720117ee66311"
+dependencies = [
+ "libc",
+]
+
 [[package]]
 name = "anstream"
 version = "0.6.4"
@@ -50,13 +65,55 @@ dependencies = [
  "windows-sys",
 ]
 
+[[package]]
+name = "autocfg"
+version = "1.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d468802bab17cbc0cc575e9b053f41e72aa36bfa6b7f55e3529ffa43161b97fa"
+
 [[package]]
 name = "bautils"
 version = "0.1.0"
 dependencies = [
+ "chrono",
  "clap",
 ]
 
+[[package]]
+name = "bumpalo"
+version = "3.14.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7f30e7476521f6f8af1a1c4c0b8cc94f0bee37d91763d0ca2665f299b6cd8aec"
+
+[[package]]
+name = "cc"
+version = "1.0.83"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f1174fb0b6ec23863f8b971027804a42614e347eafb0a95bf0b12cdae21fc4d0"
+dependencies = [
+ "libc",
+]
+
+[[package]]
+name = "cfg-if"
+version = "1.0.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "baf1de4339761588bc0619e3cbc0120ee582ebb74b53b4efbf79117bd2da40fd"
+
+[[package]]
+name = "chrono"
+version = "0.4.31"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7f2c685bad3eb3d45a01354cedb7d5faa66194d1d58ba6e267a8de788f79db38"
+dependencies = [
+ "android-tzdata",
+ "iana-time-zone",
+ "js-sys",
+ "num-traits",
+ "wasm-bindgen",
+ "windows-targets",
+]
+
 [[package]]
 name = "clap"
 version = "4.4.7"
@@ -103,12 +160,77 @@ version = "1.0.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "acbf1af155f9b9ef647e42cdc158db4b64a1b61f743629225fde6f3e0be2a7c7"
 
+[[package]]
+name = "core-foundation-sys"
+version = "0.8.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e496a50fda8aacccc86d7529e2c1e0892dbd0f898a6b5645b5561b89c3210efa"
+
 [[package]]
 name = "heck"
 version = "0.4.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "95505c38b4572b2d910cecb0281560f54b440a19336cbbcb27bf6ce6adc6f5a8"
 
+[[package]]
+name = "iana-time-zone"
+version = "0.1.58"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8326b86b6cff230b97d0d312a6c40a60726df3332e721f72a1b035f451663b20"
+dependencies = [
+ "android_system_properties",
+ "core-foundation-sys",
+ "iana-time-zone-haiku",
+ "js-sys",
+ "wasm-bindgen",
+ "windows-core",
+]
+
+[[package]]
+name = "iana-time-zone-haiku"
+version = "0.1.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f31827a206f56af32e590ba56d5d2d085f558508192593743f16b2306495269f"
+dependencies = [
+ "cc",
+]
+
+[[package]]
+name = "js-sys"
+version = "0.3.64"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c5f195fe497f702db0f318b07fdd68edb16955aed830df8363d837542f8f935a"
+dependencies = [
+ "wasm-bindgen",
+]
+
+[[package]]
+name = "libc"
+version = "0.2.149"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a08173bc88b7955d1b3145aa561539096c421ac8debde8cbc3612ec635fee29b"
+
+[[package]]
+name = "log"
+version = "0.4.20"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b5e6163cb8c49088c2c36f57875e58ccd8c87c7427f7fbd50ea6710b2f3f2e8f"
+
+[[package]]
+name = "num-traits"
+version = "0.2.17"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "39e3200413f237f41ab11ad6d161bc7239c84dcb631773ccd7de3dfe4b5c267c"
+dependencies = [
+ "autocfg",
+]
+
+[[package]]
+name = "once_cell"
+version = "1.18.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "dd8b5dd2ae5ed71462c540258bedcb51965123ad7e7ccf4b9a8cafaa4a63576d"
+
 [[package]]
 name = "proc-macro2"
 version = "1.0.69"
@@ -156,6 +278,69 @@ version = "0.2.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "711b9620af191e0cdc7468a8d14e709c3dcdb115b36f838e601583af800a370a"
 
+[[package]]
+name = "wasm-bindgen"
+version = "0.2.87"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7706a72ab36d8cb1f80ffbf0e071533974a60d0a308d01a5d0375bf60499a342"
+dependencies = [
+ "cfg-if",
+ "wasm-bindgen-macro",
+]
+
+[[package]]
+name = "wasm-bindgen-backend"
+version = "0.2.87"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5ef2b6d3c510e9625e5fe6f509ab07d66a760f0885d858736483c32ed7809abd"
+dependencies = [
+ "bumpalo",
+ "log",
+ "once_cell",
+ "proc-macro2",
+ "quote",
+ "syn",
+ "wasm-bindgen-shared",
+]
+
+[[package]]
+name = "wasm-bindgen-macro"
+version = "0.2.87"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "dee495e55982a3bd48105a7b947fd2a9b4a8ae3010041b9e0faab3f9cd028f1d"
+dependencies = [
+ "quote",
+ "wasm-bindgen-macro-support",
+]
+
+[[package]]
+name = "wasm-bindgen-macro-support"
+version = "0.2.87"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "54681b18a46765f095758388f2d0cf16eb8d4169b639ab575a8f5693af210c7b"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn",
+ "wasm-bindgen-backend",
+ "wasm-bindgen-shared",
+]
+
+[[package]]
+name = "wasm-bindgen-shared"
+version = "0.2.87"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ca6ad05a4870b2bf5fe995117d3728437bd27d7cd5f06f13c17443ef369775a1"
+
+[[package]]
+name = "windows-core"
+version = "0.51.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f1f8cf84f35d2db49a46868f947758c7a1138116f7fac3bc844f43ade1292e64"
+dependencies = [
+ "windows-targets",
+]
+
 [[package]]
 name = "windows-sys"
 version = "0.48.0"
diff --git a/Cargo.toml b/Cargo.toml
index 7743c0a..f1bd595 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -13,6 +13,9 @@ edition = "2021"
 name = "bautils"
 path = "source/main.rs"
 
+[dependencies]
+chrono = "0.4.30"
+
 [dependencies.clap]
 features = ["derive"]
 version = "4.4.7"
diff --git a/source/cli/mod.rs b/source/cli/mod.rs
index a719797..b2ca918 100644
--- a/source/cli/mod.rs
+++ b/source/cli/mod.rs
@@ -1,10 +1,28 @@
 //! The CLI definitions.
 
-pub use {crate::cli::run::run, clap::Parser};
+pub use {
+  crate::cli::run::run,
+  clap::{Parser, Subcommand},
+};
 
 mod run;
 
 /// The main CLI command.
 #[derive(Debug, Parser)]
-#[command(about, author, version)]
-pub struct Cli {}
+#[command(about, author, version, propagate_version = true)]
+pub struct Cli {
+  /// The main CLI subcommand.
+  #[command(subcommand)]
+  pub command: MainSubcommand,
+}
+
+/// The main subcommands.
+#[derive(Debug, Subcommand)]
+pub enum MainSubcommand {
+  /// The log subcommand.
+  Log {
+    /// The data to log.
+    #[arg(last = true)]
+    data_to_log: Vec<String>,
+  },
+}
diff --git a/source/cli/run.rs b/source/cli/run.rs
index b92a41d..e388a44 100644
--- a/source/cli/run.rs
+++ b/source/cli/run.rs
@@ -1,9 +1,26 @@
 //! The CLI logic.
 
-use super::{Cli, Parser};
+use {
+  crate::{
+    cli::{Cli, MainSubcommand::*, Parser},
+    logging::append_line_to_file,
+  },
+  chrono::{SecondsFormat, Utc},
+};
 
 /// Parse the CLI arguments and execute them.
 pub fn run() {
   let cli = Cli::parse();
-  dbg!(cli);
+
+  match cli.command {
+    Log { data_to_log } => {
+      let log_line = format!(
+        "{} {}",
+        Utc::now().to_rfc3339_opts(SecondsFormat::Millis, true),
+        data_to_log.join(" ")
+      );
+      println!("{}", log_line);
+      append_line_to_file("log.txt", &log_line).unwrap();
+    }
+  }
 }
diff --git a/source/logging/mod.rs b/source/logging/mod.rs
new file mode 100644
index 0000000..09af7e0
--- /dev/null
+++ b/source/logging/mod.rs
@@ -0,0 +1,14 @@
+//! All logic for logging things.
+
+use std::{fs::OpenOptions, io::prelude::*};
+
+/// Append the `log_line` to a given file at `path` and creates the file if it
+/// doesn't exist.
+pub fn append_line_to_file(
+  path: &str,
+  log_line: &str,
+) -> Result<(), std::io::Error> {
+  let mut log_file = OpenOptions::new().create(true).append(true).open(path)?;
+  writeln!(log_file, "{}", log_line)?;
+  Ok(())
+}
diff --git a/source/main.rs b/source/main.rs
index 5956483..6bee81e 100644
--- a/source/main.rs
+++ b/source/main.rs
@@ -6,6 +6,7 @@
 #![warn(missing_docs, clippy::missing_docs_in_private_items)]
 
 mod cli;
+mod logging;
 
 fn main() {
   cli::run();