How to set the subject line and add attachment while using sendmail utility on linux?

Question

I am using sendmail utility on CentOs to send mail. I am not able to set the subject-line and add attachment for the mails which are sent using this utility. Using option "-s" to set the subject line is not applicable for sendmail utility. Please tell what options to use with the sendmail for achieving thses objectives.

Answer 1

sendmail is a low-level utility. You have to compose the extra message headers yourself.

That is, to add the subject line, before the body of the message you prepend:

Subject: <your-subject>

And a new line to separate the headers from the body.

Likewise, to add the attachment:

Subject: <your-subject>
Content-Type: multipart/mixed; boundary="-unique-str"

---unique-str
Content-Type: text/html
Content-Disposition: inline

<html-body here>
---unique-str
Content-Type: application; name=<attachment-mime>
Content-Transfer-Encoding: base64
Content-Disposition: attachment; filename=<attachment-name>

<your base64-encoded attachment here>
---unique-str--

Or something like this (I didn't test it).

You can see how real messages are formatted by looking at the "show original" or "show source" options available in most e-mail clients. Those options will show you the raw-message and you just need to build something similar.