Perl for Web Site Management

Filehandles and Piped Output

Now take a look at the next section of the script:

# send the email message

open MAIL, "|$sendmail -oi -t" or die "Can't open pipe to $sendmail: $!\n";

print MAIL <<"EOF";
To: $recipient
From: $sender
Subject: Sample Web Form Submission

$mail_body
EOF

close MAIL or die "Can't close pipe to $sendmail: $!\n";

Previously, when you wanted to have your program output something, you just used Perl’s print function. When you use print from within a Perl program, whatever you print goes to your screen (if you were running the script from the shell) or to the remote user’s web browser (if you were running the script as a CGI script, and had output a suitable CGI header beforehand). In each case you were printing to what Unix users call standard output , or STDOUT, which is the default destination that the print command prints to.

You don’t have to print to STDOUT, however. You can also send our output somewhere else using something called a filehandle. Doing so is a three-step process:

1. Open the filehandle.

2. Print to the filehandle.

3. Close the filehandle.

The most common use for printing to a filehandle is to let your script store its output in a file. What we’re doing here involves a less-common use: using a filehandle to send the script’s output to another program so that the other program can do something special with it. In this case, your script is sending its output to the Unix sendmail program, so sendmail can, well, send some mail.

Programmers call this ...