How send email from command line specifying the email subject and using postfix

I'd try blat. You could write a vbscript but there is no built in executable to send mail

Well, if the emails you want to send are fairly basic, you could also just talk to your email server using basic SMTP commands and netcat.

The following bash script works just fine, it's pretty raw though...

#! /bin/bash

my_message="hello world, how's the weather today ?"
mail_srv_ip=127.0.0.1
mail_srv_port=25
recipient=jean-kevin@gmail.com

nc $mail_srv_ip $mail_srv_port << EOF
ehlo mail.script
mail from:<bashscript@local>
rcpt to:<$recipient>
data
subject: bash script email output
$message
.
quit
EOF

If the goal is to send the output of a bash script, it will work. $message can contain anything you want, smtp expects the end of the 'data' section to be marked by a line starting with a dot.