Add exec magic command to the REPL

Sometimes you want to execute a multiline script after you've already
opened the REPL and you don't want to close it and lose all state. The
exec command will let the user execute a file from the REPL while
running, just like typing the code manually.

frida_tools/_repl_magic.py

@@ -1,5 +1,7 @@
 import abc
+import codecs
 import json
+import os
 
 
 class Magic(abc.ABC):
@@ -68,6 +70,29 @@ def execute(self, repl, args):
         repl._autoperform_command(args[0])
 
 
+class Exec(Magic):
+    @property
+    def description(self):
+        return "execute the given file path in the context of the currently loaded scripts"
+
+    @property
+    def required_args_count(self):
+        return 1
+
+    def execute(self, repl, args):
+        if not os.path.exists(args[0]):
+            repl._print("Can't read the given file because it does not exist")
+            return
+
+        try:
+            with codecs.open(args[0], 'rb', 'utf-8') as f:
+                if not repl._eval_and_print(f.read()):
+                    repl._errors += 1
+        except PermissionError:
+            repl._print("Can't read the given file because of a permission error")
+
+
+
 class Time(Magic):
     @property
     def description(self):

frida_tools/repl.py

@@ -430,6 +430,7 @@ def _print_help(self, expression):
             'reload': _repl_magic.Reload(),
             'unload': _repl_magic.Unload(),
             'autoperform': _repl_magic.Autoperform(),
+            'exec': _repl_magic.Exec(),
             'time': _repl_magic.Time(),
             'help': _repl_magic.Help()
         }