How to read from a pipeline with Perl

Example 1: 

To run the date command from a Perl program, and read the output
of the command, all you need are a few lines of code like this: 

open(DATE, "date|"); 
$theDate = <DATE>; 
close(DATE); 

The open() function runs the external date command, then opens 
a file handle DATE to the output of the date command. 

Next, the output of the date command is read into 
the variable $theDate through the file handle DATE.

Example 2:

The following code runs the "ps -f" command, and reads the output:

open(PS_F, "ps -f|"); 
while (<PS_F>) { 
($uid,$pid,$ppid,$restOfLine) = split; 
# do whatever I want with the variables here ... 
} 
close(PS_F);