Got it, let’s walk through how to downgrade your system-wide Perl from 5.22 to 5.20 on Ubuntu 16.04—this should resolve the defined(@array) deprecation error that’s breaking your cgi-bin scripts. Here’s the step-by-step breakdown:

First, we need to remove the existing Perl 5.22 installation. Note that some system tools depend on Perl, so we’ll use a safe remove command to avoid wiping critical config files:

• Update your package list to ensure you have the latest repository info:
  sudo apt update
• Uninstall Perl 5.22 and its core modules:
  sudo apt-get remove perl perl-base perl-modules
• If you have additional Perl packages (like perl-doc), remove those too:
  sudo apt-get remove perl-doc

Since Ubuntu 16.04 is end-of-life, the standard repositories no longer host Perl 5.20. We’ll add the old-releases repo to access the older Perl version:

• Open your system’s sources list in a text editor:
  sudo nano /etc/apt/sources.list
• Paste these lines at the bottom of the file:

  deb http://old-releases.ubuntu.com/ubuntu/ xenial main
  deb http://old-releases.ubuntu.com/ubuntu/ xenial universe
  

• Save and exit the editor (press Ctrl+O, hit Enter, then Ctrl+X).
• Refresh your package list to pull data from the new repo:
  sudo apt update

Now install the specific Perl 5.20 packages for Ubuntu 16.04:

• Run the install command with exact version numbers to ensure you get 5.20:
  sudo apt-get install perl=5.20.2-6ubuntu1.1 perl-base=5.20.2-6ubuntu1.1 perl-modules=5.20.2-6ubuntu1.1
• Verify the installation by checking the Perl version:
  perl -v
  You should see output starting with This is perl 5, version 20, subversion 2 (v5.20.2)—that confirms the downgrade worked.

To prevent apt from automatically upgrading Perl back to 5.22, we’ll create a package pinning rule:

• Create a new pinning file:
  sudo nano /etc/apt/preferences.d/perl-pin
• Add these lines to the file to prioritize Perl 5.20:

  Package: perl perl-base perl-modules
  Pin: version 5.20.2-6ubuntu1.1
  Pin-Priority: 1001
  

• Save and exit the editor. This ensures apt will always prefer the 5.20 version over any newer ones.

With Perl 5.20 now active globally, verify your scripts work:

• First, test a script directly from the command line to catch any errors:
  perl /path/to/your/cgi/script.pl
• If that runs without the defined(@array) error, access the script via your web server (like Apache) to confirm it works in the cgi-bin context.

• System Dependency Warning: Some Ubuntu system tools rely on Perl. Downgrading might cause unexpected issues with certain system scripts. It’s wise to back up your system before proceeding, or consider using a local Perl installation (e.g., with perlbrew) as an alternative to a system-wide downgrade if your use case allows it.
• EOL Reminder: Ubuntu 16.04 is no longer supported, so you won’t receive security updates. If possible, plan to upgrade your OS to a supported version long-term to avoid security risks.

内容的提问来源于stack exchange，提问作者Will