Run "ruby" over file when file changes (useful for vim + tmux panes, or other tiled window setup. Make sure you +x this script)

ruby-it-on-file-change.sh

#!/bin/bash
#
# Usage: ./ruby-it-on-file-change.sh app.rb
# ^ Will automatically run "ruby app.rb" when file changes
#
echo "Watching for changes in $1, save this file to run \"ruby $1\""

if uname | grep -q "Darwin"; then
    mod_time_fmt="-f %m"
else
    mod_time_fmt="-c %Y"
fi

### Set initial time of file
LTIME=`stat $mod_time_fmt $1`

while true
do
   ATIME=`stat $mod_time_fmt $1`

   if [[ "$ATIME" != "$LTIME" ]]
   then
       NOW=`date +"%H:%M:%S"`
       echo "RUN COMMAND AT $NOW"
       LTIME=$ATIME
       ruby $1
   fi
   sleep 0.1
done