---
name: "Perl::Critic::Policy::InputOutput::ProhibitReadlineInForLoop"
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::ProhibitReadlineInForLoop"
---

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

Write "while( $line = \<\> ){...}" instead of "for(\<\>){...}".

## NAME

Perl::Critic::Policy::InputOutput::ProhibitReadlineInForLoop - Write "while( $line = \<\> ){...}" instead of "for(\<\>){...}".

## AFFILIATION

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

## DESCRIPTION

Using the readline operator in a `"for"` or `"foreach"` loop is very slow.  The iteration list of the loop creates a list context, which causes the readline operator to read the entire input stream before iteration even starts.  Instead, just use a `"while"` loop, which only reads one line at a time.

```
  for my $line ( <$file_handle> ){ do_something($line) }      #not ok
  while ( my $line = <$file_handle> ){ do_something($line) }  #ok
```

## CONFIGURATION

This Policy is not configurable except for the standard options.

## AUTHOR

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

## COPYRIGHT

Copyright (c) 2005-2011 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.  The full text of this license can be found in the LICENSE file included with this module.