There is no reason to declare all your variables when they are already in the $query object.

This generates a warning (uninitialized value in string eq) when button does not already exist in the $query object. 

my $query = CGI->new();

if ($query->param( "button" ) eq 'first') { display_first(  $query ) }

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Declaring variables helps keep track of what input is expected and set default values when none exists: 
my $region = $query->param( "region" ) || 42;
my $button = $query->param( "button" ) || '';
if ($button eq 'first') { # '' gives no warning

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This generates a different warning (uninitialized value in hash element): 
my $handler = $handlers{$query->param( "button" )};

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In reply to Re^2: CGI: Passing variables to a subroutine by Anonymous Monk
in thread CGI: Passing variables to a subroutine by stumbler

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