adds ability to read hosts.txt if no file is specified on the command line, using defaults if hosts.txt is missing

belleville.txt

@@ -1,3 +1,4 @@
+address,name
 10.3.100.1,Belleville Router
 10.11.31.3,Belleville VPN 11-31
 10.12.32.1,Belleville VPN 12-32

lindsay.txt

@@ -1,3 +1,4 @@
+address,name
 10.3.100.1,Belleville Router
 10.11.31.3,Belleville VPN 11-31
 10.12.32.1,Belleville VPN 12-32

src/bin/pp.rs

@@ -21,7 +21,6 @@ const SECONDS_IN_MINUTE: u32 = 60;
 const SECONDS_IN_HOUR: u32 = SECONDS_IN_MINUTE * 60;
 const SECONDS_IN_DAY: u32 = SECONDS_IN_HOUR * 24;
 
-
 pub fn duration_to_string(to_convert: Duration) -> String {
     let mut total_seconds = to_convert.as_secs() as u32;
     let mut working_string = String::new();
@@ -169,7 +168,15 @@ impl PPState {
         let settings = AppSettings::parse();
 
         print!("Prep to load targets...");
-        let mut targets = PPState::build_targets_from_file(settings.ping_host_file);
+        let file_to_check = match settings.ping_host_file {
+            None => {
+                PathBuf::from("./hosts.txt")
+            }
+            Some(actual) => {
+                actual
+            }
+        };
+        let mut targets = PPState::build_targets_from_file(Some(file_to_check));
 
         // channel to send requests to ping
         let (ping_response_sender, ping_response_listener) = mpsc::channel::<PingResult>();