feat: implement command piping in shell program

Reviewed-on: #1

renovate.json

@@ -0,0 +1,6 @@
+{
+  "$schema": "https://docs.renovatebot.com/renovate-schema.json",
+  "extends": [
+    "local>Renovate/renovate-config"
+  ]
+}

src/main.rs

@@ -1,13 +1,73 @@
-use std::{io::stdin, process::Command};
+use std::{env, io::{stdin, stdout, Write}, path::Path, process::{Child, Command, Stdio}};
 
 fn main(){
-    let mut input = String::new();
-    stdin().read_line(&mut input).unwrap();
+    loop {
+        print!("> ");
+        stdout().flush();
 
-    // read_line leaves a trailing newline, which trim removes
-    let command = input.trim(); 
+        let mut input = String::new();
+        stdin().read_line(&mut input).unwrap();
 
-    Command::new(command)
-        .spawn()
-        .unwrap();
+        // must be peekable so we know when we are on the last command
+        let mut commands = input.trim().split(" | ").peekable();
+        let mut previous_command = None;
+
+        while let Some(command) = commands.next()  {
+
+            let mut parts = command.trim().split_whitespace();
+            let command = parts.next().unwrap();
+            let args = parts;
+
+            match command {
+                "cd" => {
+                    let new_dir = args.peekable().peek()
+                        .map_or("/", |x| *x);
+                    let root = Path::new(new_dir);
+                    if let Err(e) = env::set_current_dir(&root) {
+                        eprintln!("{}", e);
+                    }
+
+                    previous_command = None;
+                },
+                "exit" => return,
+                command => {
+                    let stdin = previous_command
+                        .map_or(
+                            Stdio::inherit(),
+                            |output: Child| Stdio::from(output.stdout.unwrap())
+                        );
+
+                    let stdout = if commands.peek().is_some() {
+                        // there is another command piped behind this one
+                        // prepare to send output to the next command
+                        Stdio::piped()
+                    } else {
+                        // there are no more commands piped behind this one
+                        // send output to shell stdout
+                        Stdio::inherit()
+                    };
+
+                    let output = Command::new(command)
+                        .args(args)
+                        .stdin(stdin)
+                        .stdout(stdout)
+                        .spawn();
+
+                    match output {
+                        Ok(output) => { previous_command = Some(output); },
+                        Err(e) => {
+                            previous_command = None;
+                            eprintln!("{}", e);
+                        },
+                    };
+                }
+            }
+        }
+
+        if let Some(mut final_command) = previous_command {
+            // block until the final command has finished
+            final_command.wait();
+        }
+
+    }
 }