use strict;
use warnings;
use File::Copy;

my $source_path = "/some/path";
my $sorted_path = "/some/other/path";

# get the set of existing sorted directories:

my %sorted_dir;
opendir( SORTED, $sorted_path ) or die "$sorted_path: $!\n";
while ( my $name = readdir( SORTED )) {
    if ( -d "$sorted_path/$name" and $name =~ /^(\d+_)/ ) {
        my $dir_key = $1;
        $sorted_dir{$dir_key} = $name;
    }
}
closedir SORTED;

# go through the files to be sorted:

opendir( SOURCE, $source_path ) or die "$source_path: $!\n";
while ( my $file = readdir( SOURCE )) {
    my $src = "$source_path/$file";
    next unless ( -f $src and $file =~ /^(\d+_)/ );
    my $target_key = $1;

    if ( not exists( $sorted_dir{$target_key} )) {
        warn "No directory exists in $sorted_path to hold $file\n";
        next;
    }
    my $dest = "$sorted_path/$sorted_dir{$target_key}/$file";
    if ( -f $dest ) {
        warn "$src already exists as $dest; not copied\n";
        next;
    }
    copy( $src, $dest )
        or warn "failed to copy $src to $dest: $!\n";
}
closedir SOURCE;