#!/usr/bin/perl

use strict;
use Getopt::Long;

my $Usage = "Usage: $0 [-p path] filename.list\n   or: ls [path] | $0 [-p path]\n";

my $path = '.';
die $Usage unless ( GetOptions( 'p=s' => \$path ) and -d $path );
die $Usage if (( @ARGV and !-f $ARGV[0] ) or ( @ARGV==0 and -t ));
    # need file name args or pipeline input

my @file_list = <>;  # read all input as a list of file names
chomp @file_list;   # get rid of line-feeds

for my $name ( @file_list ) {
    my $file = "$path/$name";
    if ( ! -f $file ) {
        warn "input value '$file' does not seem to be a data file; skipped\n";
        next;
    }
    if ( ! open( I, "<", $file )) {
        warn "open failed for input file '$file'; skipped\n";
        next;
    }
    ...
}