use strict;
use warnings;

# get the list of accounts numbers we're looking for:

my %target_acc;
my $target_file = "accts_file.txt";

open( TARGS, "<", $target_file ) or die "$target_file: $!";
while (<TARGS>) {
    chomp;
    $target_acc{$_} = undef; # keep target account #' as hash keys
}
close TARGS;

# get the list of files we want to search over:

my $datadir = "/my/data/dir/with/files";

opendir( DIR, $datadir ) or die "$datadir: $!";
my @files = grep {-T "$datadir/$_"} readdir DIR;
closedir DIR;

# open each file to be searched, output found lines to
# a corresponding NEW file in the current directory

for my $file ( @files ) {
    open( OUT, ">", "NEW_$file" ) or die "NEW_$file: $!";
    if ( open( IN, "<", "$datadir/$file" )) {
        while (<IN>) {
            print if (( /^(\d{9})\|/ or /\|(\d{9})[|\r\n]/ )
                        and exists( $target_acc{$1} ));
        }
        close IN;
    }
    close OUT;
}