sh: Ngikugwema kanjani ukucacisa izincazelo zefayela ezinenombolo?

Lapho ngine

  exec 3>>file               # file descriptor 3 now points to file
  [ $dryrun ] && exec 3>&1   # or possibly to stdout
  echo "running">&3
  exec 3>&-                  # and is now closed

ngikhathazekile ngokuthi isichazi sefayela 3 kungenzeka ukuthi sasikhombe kuphi ngaphandle komsebenzi okukhulunywa ngawo. Ngingakusingatha kanjani lokhu?

• Ingabe ikhona i- builtin next_available_fd ?
• Ingabe ikhona indlela yokuphinda kabili i-fd3 iye kokuguquguqukayo, bese uyiphinda emuva uma umsebenzi usuqedile?
  • futhi ngabe kufanele ngikhathazeke ngokufaka imicu kanye kanye nokubhala okufanayo ku-fd3 kuleli cala?
• Ngiku-sh, kepha mhlawumbe i-bash / ksh / zsh inempendulo kulokhu?