---
name: "Perl::Critic::Policy::InputOutput::ProhibitTwoArgOpen"
section: "3pm"
platform: "linux"
package: "perl-perl-critic"
version: "1.156-3"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/Perl::Critic::Policy::InputOutput::ProhibitTwoArgOpen"
---

# Perl::Critic::Policy::InputOutput::ProhibitTwoArgOpen(3pm)

Write "open $fh, q{\<}, $filename;" instead of "open $fh, "\<$filename";".

## NAME

Perl::Critic::Policy::InputOutput::ProhibitTwoArgOpen - Write "open $fh, q{\<}, $filename;" instead of "open $fh, "\<$filename";".

## AFFILIATION

This Policy is part of the core Perl::Critic distribution.

## DESCRIPTION

The three-argument form of `"open"` (introduced in Perl 5.6) prevents subtle bugs that occur when the filename starts with funny characters like '\>' or '\<'.  The IO::File module provides a nice object-oriented interface to filehandles, which I think is more elegant anyway.

```
  open( $fh, '>output.txt' );          # not ok
  open( $fh, q{>}, 'output.txt' );     # ok
  use IO::File;
  my $fh = IO::File->new( 'output.txt', q{>} ); # even better!
```

It's also more explicitly clear to define the input mode of the file, as in the difference between these two:

```
  open( $fh, 'foo.txt' );       # BAD: Reader must think what default mode is
  open( $fh, '<', 'foo.txt' );  # GOOD: Reader can see open mode
```

There is also a one-argument form of `"open"` which retrieves the expression to open from the global variable with the same name as the handle, but this has the same problems as the two-argument form, and adds in more ambiguity.

```
  our $FH = '<foo.txt';
  open( FH ); # not ok
```

This policy will not complain if the file explicitly states that it is compatible with a version of perl prior to 5.6 via an include statement, e.g. by having `"require 5.005"` in it.

## CONFIGURATION

This Policy is not configurable except for the standard options.

## NOTES

There is one case in which you are forced to use the two-argument form of open: when doing a safe pipe open, as described in perlipc.

## SEE ALSO

IO::Handle

IO::File

## AUTHOR

Jeffrey Ryan Thalhammer \<jeff@imaginative-software.com\>

## COPYRIGHT

Copyright (c) 2005-2021 Imaginative Software Systems.  All rights reserved.

This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.