Builtins: Added the exit builtin

src/fsh.nim

@@ -18,10 +18,11 @@ for k, v in envPairs():
   envVariables[k]=v
 
 # list of builtin commands
-let builtins: array[3, string] = [
+let builtins: array[4, string] = [
 "set",
 "setenv",
 "echo",
+"exit",
 ]
 
 # forward declarations
@@ -214,6 +215,25 @@ proc runBuiltin(builtin: string, args: openArray[string]): string =
       if args[0] == "-n":
         return args[1..^1].join(" ")
       return args.join(" ") & "\p"
+    of "exit":
+      if args.len == 0:
+        quit(0)
+      elif args.len == 1:
+        try:
+          quit(args[0].parseInt)
+        except ValueError:
+          quit(0)
+      else:
+        try:
+          let exitcode=args[0].parseInt
+          if exitcode > 0:
+            stderr.write(args[1..^1].join(" "), "\p")
+          else:
+            stdout.write(args[1..^1].join(" "), "\p")
+          quit(exitcode)
+        except ValueError:
+          stdout.write(args.join(" "), "\p")
+          quit(0)
     else:
       raise newException(Exception, "Fsh: No such builtin implemented")