Question

What is the scalar “..” operator typical usage? Is it only selecting blocks of text?

Interesting example by myself:

sub get_next {
    print scalar($$..!$$), "\n";
}

get_next for 1 .. 5;  # prints numbers from 1 to 5
get_next for 1 .. 5;  # prints numbers from 6 to 10

Answer 1

People hardly seem to know about it based on questions here, but, yes, I’d say typical usage is selecting blocks of text, either with

while (<>) {
  print if /BEGIN/ .. /END/;
}

or

while (<>) {
  print if 3 .. 5; # prints lines 3 through 5
}

The latter is syntactic sugar for checking against the input line-number ($.)

... if $. == 3 .. $. == 5;

which suggests the weird-looking

#! /usr/bin/perl -l

for ($_ = 1; $_ <= 10; ++$_) {
  print if $_ == 4 .. $_ == 7;
}

The above program’s output is

4
5
6
7

If you have some sort of bracketing condition, test for it in subs:

for (...) {
  do_foo($x,$y,$z) if begin($x) .. end($z);
}