This works for me without a bad message:

#!/usr/bin/perl
# vi:ts=4 sw=4 et:
use strict;
use warnings;


my $fname = $ARGV[0];

my $scan_foo = 1;


eval "use File::stat";
if ( $@ ) {
     $scan_foo = 0;
}

if ( $scan_foo ) {
    my $foobarzlot = sprintf("%d", File::stat::stat($fname)->size );
    print "FOOBARZLOT=" . $foobarzlot . $/;
}

__END__
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update1: 1st answer removed due to bad reading of OP

update2: adjusted code to better match original code example