diff --git a/interactive/run b/interactive/run
index 8fcc711..4364a50 100755
--- a/interactive/run
+++ b/interactive/run
@@ -7,6 +7,7 @@
 
 $: << 'fig/lib'
 require 'execrunner'
+$optPrefix = '-'
 $path = 'interactive'
 $output = 'interactive/output'
 $modes = []
diff --git a/run b/run
index 20944eb..7f5bc89 100755
--- a/run
+++ b/run
@@ -7,6 +7,7 @@
 
 $: << 'fig/lib'
 require 'execrunner'
+$optPrefix = '-'
 
 $modes = []
 def addMode(name, description, func)