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Perl has a zoo of special variables — short names for built-in functionality. Some core ones:

$_ — the default variable:

for (1..5) {
    print "$_\n";       # $_ holds the current item
}

map { $_ * 2 } @nums;    # block uses $_ for each item
grep { $_ > 5 } @nums;

Most Perl built-ins fall back to $_ when no argument given.

@ARGV — command-line arguments:

foreach my $arg (@ARGV) { ... }
my ($input, $output) = @ARGV;

$0 — script name. Useful for die "$0: error...".

$1, $2, ... — regex capture groups:

if ("2026-05-08" =~ /(\d{4})-(\d{2})-(\d{2})/) {
    print "year: $1, month: $2, day: $3\n";
}

$/ — input record separator. Default is \n. Set to undef to slurp the whole file:

{
    local $/;     # local — restore on scope exit
    my $contents = <$fh>;
}

$\ — output record separator. Set to \n and every print adds a newline:

{
    local $\ = "\n";
    print "hello";    # "hello\n"
    print "world";    # "world\n"
}

$! — last system error message:

open(my $fh, '<', $path) or die "can't open $path: $!";

$@ — last eval error:

eval { risky_op(); };
if ($@) {
    warn "failed: $@";
}

Pragmas are special modules that change compilation behavior:

• use strict — require declarations, no soft refs
• use warnings — runtime warnings
• use utf8 — source code is UTF-8
• use feature 'say' — enable specific features (say, switch, state, etc.)
• use 5.020 — require Perl >= 5.20 + enables features
• no strict 'refs' — locally turn off (when you need glob magic)

use English — give plain names to special vars: $ARG for $_, $INPUT_RECORD_SEPARATOR for $/. Slower; mostly for readability when teaching.

local — temporarily replace a (package or special) variable in dynamic scope:

sub silence {
    local *STDERR;
    open STDERR, '>', '/dev/null';
    return inner_call();
}

my is lexical (visible in the same block); local is dynamic (visible in called functions).