add bash completion script

src/main.zig

@@ -73,6 +73,9 @@ fn printHelp() void {
         \\  show NAME              Show the code for the authenticator with name NAME
         \\
         \\Options:
+        \\  --bash                 Print script to set up Bash shell integration. Usage: add 
+        \\                              eval "$(zig-totp --bash)"
+        \\                         to your ~/.bashrc 
         \\  --config [path]        The path to a config file (default is $XDG_CONFIG_HOME/zig-totp or $HOME/.zig-totp).
         \\ 
     ;
@@ -182,7 +185,26 @@ fn parseArgs(allocator: Allocator, args: []const []const u8) !Args {
     while (i < args.len) : (i += 1) {
         const arg = args[i];
 
-        if (eql(u8, "--config", arg)) {
+        if (eql(u8, "--bash", arg)) {
+            const msg =
+                \\_zig_totp_completions()
+                \\{
+                \\   if [ "${COMP_WORDS[$COMP_CWORD-1]}" = 'show' ]
+                \\   then
+                \\      COMPREPLY=($(compgen -W "$(zig-totp list 2> /dev/null )" -- "${COMP_WORDS[$COMP_CWORD]}" ))
+                \\   elif [ "${COMP_WORDS[$COMP_CWORD-1]}" = '--config' ]
+                \\   then 
+                \\      COMPREPLY=($(compgen -A file -- "${COMP_WORDS[$COMP_CWORD]}" ))
+                \\   else 
+                \\      COMPREPLY=($(compgen -W "list show --bash --config" -- "${COMP_WORDS[$COMP_CWORD]}" ))
+                \\   fi
+                \\}
+                \\complete -F _zig_totp_completions zig-totp
+                \\
+            ;
+            try std.io.getStdOut().writer().print("{s}\n", .{msg});
+            std.process.exit(0);
+        } else if (eql(u8, "--config", arg)) {
             i += 1;
             if (i >= args.len) {
                 std.debug.print("expected a path after parameter '--config'\n  see 'zig-totp' for help\n", .{});