how do you append arrays?

[asdf via Digitalmars-d-learn]

On Thursday, 25 February 2016 at 19:21:31 UTC, Steven 
Schveighoffer wrote:
> On 2/25/16 2:12 PM, Steven Schveighoffer wrote:
>> I believe you could use std.algorithm.copy, but probably need 
>> to do it
>> with retro as well.
>>
>
> Heh, or of course use memmove :)
>
> -Steve

I got the history list working this morning but probably not very 
efficient. You can see:
---- cut ----
debug = 0;
import std.stdio;
import std.string;

void main() {
     string line;
     string[] history;
     char cmd = '/',
          sep = ';',
          dot = '.',
          bak = '\\';

     line = readln().chomp;
     foreach(int i; 0..100) history ~= "";
     debug(1) { stderr.writeln(history); }

     while(!stdin.eof) {
         string[] emit = line.split(sep);
         foreach(string e; emit) {

             /* how to do proper prefix and/or leading word? */
             if(e[0] == cmd) { /* ... */ }
             else if(e[0] == dot) { /* ... */ }
             else if(e[0] == bak) { /* ... */ }
             else writeln(e);
         }

         if(line != "" && line != history[0]) {
             string[] x = [line];
             foreach(string i; history[0..99]) x ~= i;
             history = x;
         }
         debug(1) { stderr.writeln(history); }

         line = readln().chomp;
     }
}
---- cut ----

Is there a good way to pick out matching prefixes of a string? 
Picking out the first word without disrupting whitespace after 
the second word would be nice =)

How do you read chars without waiting for a newline? That would 
be needed to respond to the ANSI esapes for arrow keys...