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Perl::Critic::Policy::ControlStructures::ProhibitPostfixControls - Write if($condition){ do_something() } instead of do_something() if $condition.


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


Conway discourages using postfix control structures (if, for, unless, until, when, while) because they hide control flow. The unless and until controls are particularly evil because they lead to double-negatives that are hard to comprehend. The only tolerable usage of a postfix if/when is when it follows a loop break such as last, next, redo, or continue.

    do_something() if $condition;           # not ok
    if ($condition) { do_something() }      # ok

    do_something() while $condition;        # not ok
    while ($condition) { do_something() }   # ok

    do_something() unless $condition;       # not ok
    do_something() unless ! $condition;     # really bad
    if (! $condition) { do_something() }    # ok

    do_something() until $condition;        # not ok
    do_something() until ! $condition;      # really bad
    while (! $condition) { do_something() } # ok

    do_something($_) for @list;             # not ok

    for my $n (0..100) {
        next if $condition;                 # ok
        last LOOP if $other_condition;      # also ok

        next when m< 0 \z >xms;             # fine too


A set of constructs to be ignored by this policy can specified by giving a value for 'allow' of a string of space-delimited keywords: if, for, unless, until, when, and/or while. An example of specifying allowed flow-control structures in a .perlcriticrc file:

    allow = for if until

By default, all postfix control keywords are prohibited.

The set of flow-control functions that are exempt from the restriction can also be configured with the 'flowcontrol' directive in your .perlcriticrc file:

    flowcontrol = warn die carp croak cluck confess goto exit

This is useful if you're using additional modules that add things like assert or throw.


The die, croak, and confess functions are frequently used as flow-controls just like next or last. So this Policy does permit you to use a postfix if when the statement begins with one of those functions. It is also pretty common to use warn, carp, and cluck with a postfix if, so those are allowed too.

The when keyword was added to the language after Perl Best Practices was written. This policy treats when the same way it does if, i.e. it's allowed after flow-control constructs. Thanks to brian d foy for the inspiration.


Look for the do {} while case and change the explanation to point to page 123 when it is found. RT #37905.


Jeffrey Ryan Thalhammer <>


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.