Perl

#!/usr/bin/perl

# This is a comment

print "Hello world\n";

here-doc

$a = 10;
$var = <<"EOF";
This is the syntax for here document and it will continue
until it encounters a EOF in the first line.
This is case of double quote so variable value will be
interpolated. For example value of a = $a
EOF
print "$var\n";

$var = <<'EOF';
This is case of single quote so variable value will be
interpolated. For example value of a = $a
EOF
print "$var\n";

Identifiers

A Perl identifier is a name used to identify a variable, function, class, module, or other object.

A Perl variable name starts with either $, @ or % followed by [0-9a-z_]+