Builtins: Added set, setenv, and echo builtins

src/fsh.nim

@@ -7,6 +7,7 @@ import streams
 import osproc
 import strtabs
 import os
+import strutils
 
 # globals
 var shellVariables = newStringTable(modeCaseSensitive)
@@ -16,6 +17,13 @@ var envVariables = newStringTable(modeCaseSensitive)
 for k, v in envPairs():
   envVariables[k]=v
 
+# list of builtin commands
+let builtins: array[3, string] = [
+"set",
+"setenv",
+"echo",
+]
+
 # forward declarations
 proc eval(cmd: string): string
 proc substitute(strm: Stream, delim = ";\p"): string
@@ -185,11 +193,38 @@ proc parseCommand(cmd: string): seq[string] =
         discard strm.skipSpaces()
       else: newitem.add(c)
 
+# runBuiltin runs a shell builtin
+proc runBuiltin(builtin: string, args: openArray[string]): string =
+  case builtin:
+    of "set":
+      if args.len < 2:
+        raise newException(Exception, "Set: not enough arguments provided")
+      shellVariables[args[0]] = args[1..^1].join(" ")
+      return ""
+    of "setenv":
+      if args.len < 2:
+        raise newException(Exception, "setenv: Not enough arguments provided")
+      try:
+        envVariables[args[0]] = args[1..^1].join(":")
+        putEnv(args[0], args[1..^1].join(":"))
+      except OSError as e:
+        raise newException(Exception, "setenv: " & e.msg)
+      return ""
+    of "echo":
+      if args[0] == "-n":
+        return args[1..^1].join(" ")
+      return args.join(" ") & "\p"
+    else:
+      raise newException(Exception, "Fsh: No such builtin implemented")
+
 # executes executes the command. For now it involves catting the command and printing it
 proc execute(cmd: string): int =
   let parsed = cmd.parseCommand
   let progname = parsed[0]
   let args = parsed[1..parsed.high]
+  if progname in builtins:
+    stdout.write(runBuiltin(progname, args))
+    return 0
   let ps = startProcess(progname, args=args, options={poUsePath, poParentStreams})
   result =  ps.waitForExit
   ps.close
@@ -199,6 +234,8 @@ proc eval(cmd: string): string =
   let parsed = cmd.parseCommand
   let progname=parsed[0]
   let args = parsed[1..parsed.high]
+  if progname in builtins:
+    return runBuiltin(progname, args)
   let ps = startProcess(progname, args=args, options={poUsePath})
   result=ps.outputStream.readAll
   ps.close