The directory entry is gone, yes. Writing to a file doesn't create directory entries.

I didn't mention glob at all. Did you try the steps I described? The file is only gone once no directory and no file handles reference it. Also, see the post I just made in parallel to yours.

$ perl -Mv5.10 -e'
   open my $o_fh, ">", "a" or die $!;
   open my $i_fh, "<", "a" or die $!;
   unlink "a" or die $!;
   print $o_fh "abc\n" or die $!;
   $o_fh->flush();
   chomp( my $line = <$i_fh> );
   say "<$line>";
'
<abc>
[download]

> See the post I just made in parallel to yours.

I know about inodes

But the question remains:

How can I revive/move an "invisible" file into the directory?

link doesn't seem to accept FHs.

use strict;
use warnings;
use Data::Dump qw/ddx/;
use autodie;



my $dir  = "/tmp";
my $file = "$dir/tst_unlink";

open my $fh, ">>", $file;

print $fh "ENTRY ".__LINE__;

ddx <$file*>;

unlink $file;

print $fh "ENTRY ".__LINE__;

ddx <$file*>;

eval { link $fh, "${file}_new"; } or warn $@;

eval { link $file, "${file}_new"; } or warn $@;


ddx <$file*>;

__DATA__
[download]

OUTPUT:

# open_unlink.pl:16: "/tmp/tst_unlink"
# open_unlink.pl:22: ()
Can't link($fh, '/tmp/tst_unlink_new'): Datei oder Verzeichnis nicht g
+efunden at ./open_unlink.pl line 24
Can't link('/tmp/tst_unlink', '/tmp/tst_unlink_new'): Datei oder Verze
+ichnis nicht gefunden at ./open_unlink.pl line 26
# open_unlink.pl:29: ()
[download]

Cheers Rolf
_{(addicted to the Perl Programming Language :)
Wikisyntax for the Monastery}

PS: FWIW: I was guessing, I can't run a full diagnosis for every fuzzy bug question, even after reading it thrice.

How can I revive/move an "invisible" file into the directory?

I hadn't read the second half of your post, just the part I commented on.

I don't know if it's possible. I doubt there exists a portable solution, but I suspect Linux might have one.