#!/usr/bin/perl -wT

$ENV{PATH} = "";
# ... use statements and other code

my @files = <../data/texts/*>;

my $file = param("select") || $files[rand(@files)];
($file) = ($file =~ /^([\w.-]+)$/);         # Clean filename
die "Invalid filename: $file" unless $file; # Die if empty

my %isfile;
undef @isfile{@files};
exists $isfile{$file} or die "Invalid filename: $file";

open(IN, "<", "../data/texts/$file") or die $!;