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);

Why is it hard to call this function: sub y { "because" }
Because y is a kind of quoting operator.
The y/// operator is the sed-savvy synonym for tr///. That means y(3) would be like tr(), which would be looking for a second string, as in tr/a-z/A-Z/, tr(a-z)(A-Z), or tr[a-z][A-Z].

What does `$result = f() .. g()' really return?
False so long as f() returns false, after which it returns true until g() returns true, and then starts the cycle again.
This is scalar not list context, so we have the bistable flip-flop range operator famous in parsing of mail messages, as in `$in_body = /^$/ .. eof()'. Except for the first time f() returns true, g() is entirely ignored, and f() will be ignored while g() later when g() is evaluated. Double dot is the inclusive range operator, f() and g() will both be evaluated on the same record. If you don't want that to happen, the exclusive range operator, triple dots, can be used instead. For extra credit, describe this:
$bingo = ( a() .. b() ) ... ( c() .. d() );

Why does Perl not have overloaded functions?
Because you can inspect the argument count, return context, and object types all by yourself.
In Perl, the number of arguments is trivially available to a function via the scalar sense of @_, the return context via wantarray(), and the types of the arguments via ref() if they're references and simple pattern matching like /^\d+$/ otherwise. In languages like C++ where you can't do this, you simply must resort to overloading of functions.

What does read() return at end of file?
0
A defined (but false) 0 value is the proper indication of the end of file for read() and sysread().