At this point, if you're a typical code hacker, you're probably wondering how to get a value into a Perl program. Here's the simplest way. Each time you use <STDIN>1 in a place where a scalar value is expected, Perl reads the next complete text line from standard input (up to the first newline), and uses that string as the value of <STDIN>. Standard input can mean many things, but unless you do something uncommon, it means the terminal of the user who invoked your program (probably you). If there's nothing waiting to be read (typically the case, unless you type ahead a complete line), the Perl program will stop and wait for you to enter some characters followed by a newline (carriage return / linefeed).2
The string value of <STDIN> typically has a newline on the end of it.3 So, you could do something like this:
$line = <STDIN>;
if ($line eq "\n") {
print "That was just a blank line!\n";
}
else {
print "That line of input was: $line";
}
But in practice, you don't often want to keep the newline, so you need the previously seen chomp function.
Next: Output with print