Question

Out of curiosity, is it possible to create, instantiate, or otherwise access additional output buffers besides STDOUT and STDERR from within a Perl script?

The use case would be additional outputs to pipe in to files or other commands, eg ./doublerainbow.pl 3>full_on.txt 4>all_the_way!.txt

Answer 1

Absolutely. The open command with the >&= mode allows you to open filehandles on arbitrary file descriptors.

# perl 4fd.pl > file1 2> file2 3> file3 4> file4 5< file5

open NONSTDFOO, '>&=3';
open NONSTDBAR, '>&=4';
open NONSTDBAZ, '<&=5';   # works for input handles, too

print STDOUT "hello\n";
print STDERR "world\n";
print NONSTDFOO "42\n";
print NONSTDBAR <NONSTDBAZ>;

---

$ echo pppbbbttt > file5
$ perl 4fd.pl >file1 2>file2 3>file3 4>file4 5<file5
$ cat file1
hello
$ cat file3
42
$ cat file4 file2
pppbbbttt
world