#!/usr/bin/perl
use strict;
use warnings;
use Data::Dumper;

$| = 1; # turn on autoflush

my $file = 'file.txt';

open my $fh, "<", $file
    or die "Could not open '$file': $!";

chomp(my @files = <$fh>);

close $fh
    or die "Coould not close '$file' $!";

while (my $stdin = <>) {
    chomp $stdin;
    last if $stdin eq ""; # exit stdin if empty string

    if ( grep { lc $stdin eq $_ } @files ) {
    print Dumper \@files;
    }
    else {
    print "There is no word in the $file\n";
    }
}

__DATA__

$ perl file.pl
DATA1
$VAR1 = [
          'data1',
          'data2',
          'data3',
          'data4'
        ];
data1
$VAR1 = [
          'data1',
          'data2',
          'data3',
          'data4'
        ];
DATA100
There is no word in the file.txt