Thank you very much for that tip! Here is an example of how it could be used:

arun@butterfly:~> perl -de 0

Loading DB routines from perl5db.pl version 1.23
Editor support available.

Enter h or `h h' for help, or `man perldebug' for more help.

main::(-e:1):   0
  DB<1> open $fh, '>', 'temp.txt'

  DB<2> x $fh
0  GLOB(0x816b940)
   -> *main::$fh
         FileHandle({*main::$fh}) => fileno(6)
  DB<3> $d = fileno $fh

  DB<4> p $d
6
  DB<5> p qx[ls /proc/$$/fd]
0
1
2
3
4
5
6
7

  DB<6> p readlink("/proc/$$/fd/$d")
/home/arun/temp.txt
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