I use this script to send myself iMessages from my server at www.MacMiniColo.net when I need to know something (i.e. backup completed, diskspace getting low, etc). I got the idea from http://www.tenshu.net/2015/02/send-imessage-and-sms-with-applescript.html

imsg.sh

#!/bin/zsh -f

### Change this to be your iMessage email account
MY_IMESSAGE='[email protected]'
### You should not need to change anything else
### I suggest saving this to /usr/local/bin/imsg.sh
### then `chmod 755 /usr/local/bin/imsg.sh`

###################################################################################################
# This is the name of the script without the path or the extension, so 'imsg' if you
# use the name I've recommended
SCRIPT_NAME="$0:t:r"

if [ "$#" = "0" ]
then
  echo "Usage: $NAME message that you want to send"
  exit 1
fi

# This is whatever input you've given to the script 
MSG="$@"

# Here's where we send it 
/usr/bin/osascript <<EOT
tell application "Messages"
  send "${MSG} [via $SCRIPT_NAME]" to buddy "$MY_IMESSAGE" of (service 1 whose service type is iMessage)
end tell
EOT

exit 0
#
# Purpose: Send iMessages from to myself from the command line.
# Adapted from: http://www.tenshu.net/2015/02/send-imessage-and-sms-with-applescript.html
#
# From:	Tj Luo.ma
# Mail:	luomat at gmail dot com
# Web: 	http://RhymesWithDiploma.com
# Date:	2015-02-21
#
#EOF