From 4d9cbbd4130c440591e7c18946bb76ee4e8b0965 Mon Sep 17 00:00:00 2001
From: Nathan Fisher <jeang3nie@hitchhiker-linux.org>
Date: Tue, 10 Jan 2023 18:28:33 -0500
Subject: [PATCH] Add `which` applet

---
 src/cmd/fold/mod.rs   |  5 ++-
 src/cmd/mod.rs        |  7 +++--
 src/cmd/which/mod.rs  | 73 +++++++++++++++++++++++++++++++++++++++++++
 src/cmd/whoami/mod.rs |  2 +-
 4 files changed, 83 insertions(+), 4 deletions(-)
 create mode 100644 src/cmd/which/mod.rs

diff --git a/src/cmd/fold/mod.rs b/src/cmd/fold/mod.rs
index df5b2db..32f22aa 100644
--- a/src/cmd/fold/mod.rs
+++ b/src/cmd/fold/mod.rs
@@ -1,6 +1,9 @@
 use super::Cmd;
 use clap::{value_parser, Arg, ArgAction, ArgMatches, Command};
-use std::{fs::File, io::{self, BufRead, BufReader}};
+use std::{
+    fs::File,
+    io::{self, BufRead, BufReader},
+};
 use textwrap::{fill, wrap_algorithms::WrapAlgorithm};
 
 #[derive(Debug)]
diff --git a/src/cmd/mod.rs b/src/cmd/mod.rs
index 3747d44..c245191 100644
--- a/src/cmd/mod.rs
+++ b/src/cmd/mod.rs
@@ -32,6 +32,7 @@ pub mod shitbox;
 pub mod sleep;
 mod sync;
 pub mod r#true;
+pub mod which;
 pub mod whoami;
 pub mod yes;
 
@@ -39,7 +40,7 @@ pub use {
     self::hostname::Hostname, base32::Base32, base64::Base64, basename::Basename,
     bootstrap::Bootstrap, dirname::Dirname, echo::Echo, factor::Factor, fold::Fold, head::Head,
     mountpoint::Mountpoint, nologin::Nologin, nproc::Nproc, r#false::False, r#true::True, rev::Rev,
-    shitbox::Shitbox, sleep::Sleep, whoami::Whoami, yes::Yes,
+    shitbox::Shitbox, sleep::Sleep, which::Which, whoami::Whoami, yes::Yes,
 };
 
 pub trait Cmd: fmt::Debug + Sync {
@@ -68,13 +69,14 @@ pub fn get(name: &str) -> Option<Box<dyn Cmd>> {
         "shitbox" => Some(Box::new(Shitbox::default())),
         "sleep" => Some(Box::new(Sleep::default())),
         "true" => Some(Box::new(True::default())),
+        "which" => Some(Box::new(Which::default())),
         "whoami" => Some(Box::new(Whoami::default())),
         "yes" => Some(Box::new(Yes::default())),
         _ => None,
     }
 }
 
-pub static COMMANDS: [&'static str; 20] = [
+pub static COMMANDS: [&'static str; 21] = [
     "base32",
     "base64",
     "basename",
@@ -93,6 +95,7 @@ pub static COMMANDS: [&'static str; 20] = [
     "sleep",
     "shitbox",
     "true",
+    "which",
     "whoami",
     "yes",
 ];
diff --git a/src/cmd/which/mod.rs b/src/cmd/which/mod.rs
new file mode 100644
index 0000000..354289d
--- /dev/null
+++ b/src/cmd/which/mod.rs
@@ -0,0 +1,73 @@
+use super::Cmd;
+use clap::{Arg, Command};
+use std::{env, fs::File, io, os::unix::prelude::MetadataExt, path::PathBuf, process};
+
+#[derive(Debug, Default)]
+pub struct Which;
+
+impl Cmd for Which {
+    fn name(&self) -> &str {
+        "which"
+    }
+
+    fn cli(&self) -> clap::Command {
+        Command::new("which")
+            .about("Write the full path of COMMAND(s) to standard output")
+            .author("Nathan Fisher")
+            .version(env!("CARGO_PKG_VERSION"))
+            .arg(Arg::new("COMMAND").num_args(1..))
+    }
+
+    fn run(&self, matches: Option<&clap::ArgMatches>) -> Result<(), Box<dyn std::error::Error>> {
+        let Some(matches) = matches else {
+            return Err(Box::new(io::Error::new(io::ErrorKind::Other, "no input")));
+        };
+        let rawpath = if let Ok(p) = env::var("PATH") {
+            p
+        } else {
+            "/usr/bin:/bin".to_string()
+        };
+        let path: Vec<_> = rawpath.split(':').collect();
+        let mut failures = 0;
+        if let Some(commands) = matches.get_many::<String>("COMMAND") {
+            for command in commands {
+                match which(command, &path) {
+                    Some(p) => println!("{p}"),
+                    None => {
+                        println!("{}: no {} in ({})", self.name(), command, &rawpath);
+                        failures += 1;
+                    }
+                }
+            }
+        } else {
+            let _res = self.cli().print_help();
+            process::exit(255);
+        }
+        if failures > 0 {
+            process::exit(failures);
+        } else {
+            Ok(())
+        }
+    }
+
+    fn path(&self) -> Option<crate::Path> {
+        Some(crate::Path::UsrBin)
+    }
+}
+
+fn which(command: &str, path: &[&str]) -> Option<String> {
+    for p in path {
+        let file = [p, command].iter().collect::<PathBuf>();
+        if file.exists() {
+            if let Ok(exe) = File::open(&file) {
+                if let Ok(meta) = exe.metadata() {
+                    let mode = meta.mode();
+                    if mode & 0o111 != 0 {
+                        return Some(format!("{}", file.display()));
+                    }
+                }
+            }
+        }
+    }
+    None
+}
diff --git a/src/cmd/whoami/mod.rs b/src/cmd/whoami/mod.rs
index 2071e5a..207ce6e 100644
--- a/src/cmd/whoami/mod.rs
+++ b/src/cmd/whoami/mod.rs
@@ -1,9 +1,9 @@
 use std::ffi::CStr;
 
 use {
+    super::Cmd,
     clap::Command,
     libc::{geteuid, getpwuid},
-    super::Cmd,
 };
 
 #[derive(Debug, Default)]