At this point, you’re probably wondering how to get a value from the keyboard into a Perl program. Here’s the simplest way: use the line-input operator, <STDIN>.^[57]

Each time you use <STDIN> in a place where Perl expects a scalar value, 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 keyboard of the user who invoked your program (probably you). If there’s nothing waiting for <STDIN> to 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 (return).^[58]