Add usage info.

diff --git a/linux/plan2icalendar b/linux/plan2icalendar
index d22965dd67ffa7b486f86378e1fd7dbb074a064a..4571fc1ab5841405066dac2723eb2e9df28e4a17 100755 (executable)
--- a/linux/plan2icalendar
+++ b/linux/plan2icalendar
@@ -38,6 +38,13 @@ exit 0;
 
 sub usage {
     print <<EOF
+Usage: $0 [-i] [-f infile] [-o outfile]
+
+Imports or exports between plan and iCalendar.
+
+  -i          import ical file
+  -f infile   read input from 'infile'
+  -o outfile  read output from 'outfile'
 EOF
 }
 sub read_planfile {