$ cat file1 file2 file3 > file123
[download]

And on Win32, copy src1+src2+src3 destination will do it.

"One word of warning: if you meet a bunch of Perl programmers on the bus or something, don't look them in the eye. They've been known to try to convert the young into Perl monks." - Frank Willison

The only error I can see is that

The coding is actually good, btw - not very idiomatic, so a bit awkward, but you obviously understand what's going on behind the scenes. Nice effort.

The only thing I can see here is I wouldn't open combine.csv every time through the loop anew, and wouldn't slurp the input file into an array.

open(OUTF,">>combine.csv") or dienice("Can't open CSV file: $!");
foreach my $file ( @files ) {
    open(INF,"$file") or dienice("Can't open data file: $!");
    print OUTF while <INF>;
    close(OUTF);
}
close(INF);
[download]

Update: nevermind, the above proposals are better.. duh. :-)

Makeshifts last the longest.

use File::Copy;
...
open(OUTF, ">combine.csv") or die "Error opening combine.csv: $!";
for my $file (@files) {
 copy($file, \*OUTF) or die "Error copying $file: $!";
}
close OUTF;
[download]

Nothing to add to other monks' comments, but only a few minor advices.

1. You could move the line $dir =~ s/\/$//; just a few lines up and avoid repeating the substitution if more than one .csv file is found in the same $dir. E.g.:

while ( my $dir = shift @ARGV ) {
    my $dh = new DirHandle $dir;
    if ( defined($dh) ) {
        $dir =~ s/\/$//; # Here, for example...
        while ( defined($_ = $dh->read) ) {
            if ( $_ =~ /(\.csv)$/ ) {
                push @files, "$dir/$_";
            }
        }
    }
}
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2. Also, you could slightly simplify your s/// by using another delimiter, for example: s|/$||. It's not a big saving with one slash, but it's worth changing the delimiter when your pattern contains a lot of them

3. When you manipulate $_ you could want to localize it, to avoid clashes with functions or modules that use it (like File::Find, for example). It's not the case of your simple program, of course.

4. (but I guess you already know :-) if you want, you can leave out the $_ =~ from your pattern match.

Just my 0.02 EUR

Ciao!
--bronto

# Another Perl edition of a song:
# The End, by The Beatles
END {
  $you->take($love) eq $you->made($love) ;
}