Perl::Critic::Policy::InputOutput::ProhibitJoinedReadline - Use local $/ = undef or Path::Tiny instead of joined readline.


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


It's really easy to slurp a whole filehandle in at once with join q{}, <$fh>, but that's inefficient -- Perl goes to the trouble of splitting the file into lines only to have that work thrown away.

To save performance, either slurp the filehandle without splitting like so:

  do { local $/ = undef; <$fh> }

or use Path::Tiny, which is even faster.

Note that if the ProhibitPunctuationVars policy is also in effect, it will complain about the use of $/ in the line above. In that case, write this instead:

  use English '-no_match_vars';

  do { local $INPUT_RECORD_SEPARATOR = undef; <$fh> };


This Policy is not configurable except for the standard options.


Due to a bug in the current version of PPI (v1.119_03) and earlier, the readline operator is often misinterpreted as less-than and greater-than operators after a comma. Therefore, this policy only works well on the empty filehandle, <>. When PPI is fixed, this should just start working.


Initial development of this policy was supported by a grant from the Perl Foundation.


Chris Dolan <>


Copyright (c) 2007-2021 Chris Dolan. Many 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