Winking Fat Comma Operator

2026-01-20

Filehandles in Perl are weird. Opening a file for output:

open(my $fh, '>', $filename);

That > is a mode indicator. But what if $filename starts with >?

open(my $fh, '>', '>dangerous');

Does that open a file called ">dangerous" or append to "dangerous"?

Enter the winking fat comma:

+>

Filehandle protection. A mode indicator that can't be confused.

Part 1: THE PROBLEM

Two-argument open is dangerous:

open(FH, $file);

If $file is "> /etc/passwd", you've just clobbered your password file.

Three-argument open is safer:

open(my $fh, '<', $file);

The mode is separate from the filename. But even here, weird filenames can cause issues or confusion.

Part 2: THE SOLUTION

Prefix the mode with +:

open(my $fh, '+>', $filename);    # Read-write, truncate
open(my $fh, '+<', $filename);    # Read-write, preserve

Wait, that's just read-write mode. Where's the winking fat comma?

The "winking fat comma" is actually using +> (or +<) to make your intentions crystal clear, especially in ambiguous situations:

open(my $fh, '+<', '>weird');     # Opens file literally named ">weird"

      .--.
     |o_o |
     |:_/ |
    //   \ \
   (|     | )
  /'\_   _/`\
  \___)=(___/

Part 3: ACTUALLY, LET'S BE HONEST

The "winking fat comma" is one of the more obscure entries in the secret operators list. The term refers to using +> in places where you want to emphasize that the > is a mode, not part of a filename.

open(my $fh, "+>", $file);

The + "winks" at you, saying "this > is definitely a mode indicator."

It's more about documentation and clarity than functionality.

Part 4: THE REAL LESSON

Always use three-argument open:

open(my $fh, '<', $filename) or die "Can't read $filename: $!";
open(my $fh, '>', $filename) or die "Can't write $filename: $!";
open(my $fh, '>>', $filename) or die "Can't append $filename: $!";

The mode and filename are separate. No ambiguity.

The + modes add read-write capability:

+<    Read-write, file must exist, preserve contents
+>    Read-write, create/truncate file

Part 5: DANGEROUS FILENAMES

Files that could cause problems:

>file           Looks like output redirect
file|           Looks like pipe
|command        Looks like command
-               Looks like STDIN

Three-argument open handles all of these:

my $scary = "|rm -rf /";
open(my $fh, '<', $scary);    # Opens literal file, not a pipe

The < forces read mode. The filename is just a filename.

Part 6: THE FAT COMMA ITSELF

While we're here, the actual "fat comma":

=>

It's called fat because it's wider than a regular comma. And it auto-quotes the left side:

my %hash = (
    key => 'value',    # 'key' is auto-quoted
    foo => 'bar',
);

Same as:

my %hash = (
    'key', 'value',
    'foo', 'bar',
);

Part 7: THE WINK

So why "winking fat comma"?

+>

+    Looks like a cross or plus sign
>    Looks like... greater than? Arrow?

Together: +>

If you squint and tilt your head:

+>
 \
  O  <- that's the wink?

Honestly, this one's a stretch. The Perl community loves naming things, and sometimes the names are more memorable than meaningful.

Part 8: PRACTICAL USAGE

When you actually use +> in real code:

# Create a temp file, read and write
open(my $tmp, '+>', undef) or die "Can't create temp: $!";
print $tmp "data\n";
seek($tmp, 0, 0);
my $content = <$tmp>;

The undef as filename creates an anonymous temp file.

# Read-write an existing file
open(my $fh, '+<', 'config.txt') or die "Can't open: $!";
my @lines = <$fh>;
seek($fh, 0, 0);
truncate($fh, 0);
print $fh @modified_lines;

Read, modify, write back.

Part 9: THE MODES CHEAT SHEET

MODE    READ    WRITE   CREATE  TRUNCATE  POSITION
-------------------------------------------------------
<       Yes     No      No      No        Start
>       No      Yes     Yes     Yes       Start
>>      No      Yes     Yes     No        End
+<      Yes     Yes     No      No        Start
+>      Yes     Yes     Yes     Yes       Start
+>>     Yes     Yes     Yes     No        End

The + adds read capability to write modes (and vice versa).

Part 10: THE HONEST ASSESSMENT

Look, the "winking fat comma" isn't really a thing in the same way that the goatse operator or butterfly operator are things.

It's more of an entry in the secret operators catalog that makes people go "huh, I guess you could call it that."

The real takeaway: use three-argument open. Always. And understand the + modes for read-write operations.

Part 11: ACTUALLY USEFUL THINGS

If you're here for filehandle protection, here's what matters:

# ALWAYS use three-argument open
open(my $fh, '<', $file) or die "Can't open $file: $!";

# ALWAYS use lexical filehandles (my $fh)
# Not barewords (FH) which are global

# ALWAYS check for errors
# or die, or use autodie

use autodie;    # Now all opens die on failure automatically

That's the real secret. Not the winking fat comma.

Part 12: THE NAME EXPLAINED

Fat comma: =>

Winking: adding + to make +> or +<

Together: winking fat comma

It's a play on words. The + is the wink. The > or < after it makes it look like the fat comma's cousin.

=>     Fat comma
+>     Winking fat comma (allegedly)

The Perl community enjoys whimsical naming. This one's just not as clever as the others.

                +>
               /  \
              +    >
             /      \
          wink      arrow

     More cute than useful, honestly