The trick is to use a subroutine for the repeated code:

#!/usr/bin/perl
use warnings;
use strict;

use Tk;

sub create_entry {
    my ($parent, $entries) = @_;
    push @$entries, undef;
    $parent->Entry(-textvariable => \$entries->[$#$entries])
        ->pack;
}


my $mw = 'Tk::MainWindow'->new(-title => 'Adding entries');
my $frame = $mw->Frame->pack;

my @entries;
create_entry($frame, \@entries) for 1 .. 4;

$mw->Button(-text => '+',
            -command => [ \&create_entry, $frame, \@entries ])->pack;
$mw->Button(-text => 'Done',
            -command => sub { $mw->DESTROY })->pack;

MainLoop();

print "$_\n" for @entries;
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($q=q:Sq=~/;[c](.)(.)/;chr(-||-|5+lengthSq)`"S|oS2"`map{chr |+ord
}map{substrSq`S_+|`|}3E|-|`7**2-3:)=~y+S|`+$1,++print+eval$q,q,a,
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