Pipes

Perl can use the open routine to run shell commands and read or write to them in the manner of C's popen(3S) call.

If a file name argument starts with the pipe character (|), the file name is treated as a command. The command is then executed and the program can be sent input via the print command.

If the file name argument ends with a pipe, the command is executed and that command's output can be read using the <...> facility. Here are two examples:

open(MAIL,"| Mail root");   # send mail to root
print MAIL "user \"pat\" is up to no good\n";
close MAIL;                 # mail is now sent

open(WHO,"who|");   # see who's on the system
while ($who = <WHO>)
{
    chop $who;
    ($user,$tty,$junk) = split(/\s+/,$who,3);
    print "$user is logged on to terminal $tty\n";
}
close(WHO);