The simple method: /bin/mail

For simple applications, it may be sufficient to invoke mail
(usually `/bin/mail', but could be `/usr/bin/mail' on some
systems).

WARNING: Some versions of UCB Mail may execute commands
prefixed by `~!' or `~|' given in the message body even in
non-interactive mode. This can be a security risk.

Invoked as `mail -s 'subject' recipients...' it will take a message
body on standard input, and supply a default header (including the
specified subject), and pass the message to sendmail for
delivery.

This example mails a test message to root on the local system:

#include <stdio.h>





#define MAILPROG "/bin/mail"





int main()


{


    FILE *mail = popen(MAILPROG " -s 'Test Message' root", "w");


    if (!mail)


    {


        perror("popen");


        exit(1);


    }





    fprintf(mail, "This is a test.\n");





    if (pclose(mail))


    {


        fprintf(stderr, "mail failed!\n");


        exit(1);


    }


}

If the text to be sent is already in a file, then one can do:

    system(MAILPROG " -s 'file contents' root </tmp/filename");

These methods can be extended to more complex cases, but there are many
pitfalls to watch out for:

• 
  
  If using system() or popen(), you must be very careful about quoting
  arguments to protect them from filename expansion or word splitting
  
  
• 
  
  Constructing command lines from user-specified data is a common source
  of buffer-overrun errors and other security holes
  
  
• 
  
  This method does not allow for CC: or BCC: recipients to be specified
  (some versions of /bin/mail may allow this, some do not)