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:
Open the filehandle.
Print to the filehandle.
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 ...