added the PRIDE_DEFAULT env var to set the default flag

man/pride.6

@@ -82,6 +82,13 @@ The rainbow flag designed for 2017 Philadelphia Pride.
 .It Ic transgender, trans
 The transgender pride flag designed by Monica Helms in 1999.
 .El
+.Sh ENVIRONMENT
+.Bl -tag -width Ds
+.It PRIDE_DEFAULT
+A string containing the name of a flag to use as the default when no 
+.Ar flag
+argument is provided.
+.El
 .Sh EXIT STATUS
 .Bl -tag -width Ds
 .It 1

src/main.rs

@@ -1,4 +1,5 @@
 //!	main method module
+use std::env::var;
 
 use pico_args::Arguments;
 
@@ -50,7 +51,7 @@ fn main() {
 
 	let state = State::new(&mut args);
 
-	let subcommand = args.subcommand().unwrap();
+	let subcommand = if let Ok(Some(subcommand)) = args.subcommand() { Some(subcommand) } else { var("PRIDE_DEFAULT").ok() };
 	let variant = args.subcommand().unwrap();
 
 	//	get color vec from matched flag