Ubuntu – Make “apt-get update” show the exact output as `apt update`

apt

I'm learning the CLI interface of Advanced Packaging Tool. From the output of apt(8) when its stdout isn't a terminal, it isn't suitable for "scripts expecting stable programming interface", so I'm taking a look at apt-get(8).

One difference between apt update and apt-get update is that the latter is missing a final line after all cache has been updated:

8 packages can be upgraded. Run 'apt list --upgradable' to see them.

I want to know how I can get this exact line displayed with apt-get(8).

Best Answer

man apt-get shows:

   -s, --simulate, --just-print, --dry-run, --recon, --no-act
       No action; perform a simulation of events that would occur based on
       the current system state but do not actually change the system.
       Locking will be disabled (Debug::NoLocking) so the system state
       could change while apt-get is running. Simulations can also be
       executed by non-root users which might not have read access to all
       apt configuration distorting the simulation. A notice expressing
       this warning is also shown by default for non-root users
       (APT::Get::Show-User-Simulation-Note). Configuration Item:
       APT::Get::Simulate.

So if you just do:

apt-get upgrade --dry-run

it will output:

...
4 to upgrade, 0 to newly install, 0 to remove and 0 not to upgrade.
...

Related Solutions

APT – Resolving ‘Unstable CLI Interface’ Warning

apt is for the terminal and gives beautiful output while apt-get and apt-cache are for scripts and give stable, parsable output. The script equivalent of your apt show command therefore is:

apt-cache show $PACKAGE_NAME >pack_info.txt

Now to answer your questions one by one:

What do we exactly mean by Stable CLI Interface?

apt's output is not well usable in scripts. For example, apt install (compared to apt-get install) displays a progress bar that's useless for scripts and can throw errors when the output is parsed. apt show firefox shows a hint for an additional record, which is also totally useless in a script, you want it to simply output every record there – that's what apt-cache show firefox does. Let's see what man apt has to say about that:

The apt(8) commandline is designed as an end-user tool and it may change behavior between versions. While it tries not to break backward compatibility this is not guaranteed either if a change seems beneficial for interactive use.

All features of apt(8) are available in dedicated APT tools like apt-get(8) and apt-cache(8) as well. apt(8) just changes the default value of some options (see apt.conf(5) and specifically the Binary scope). So you should prefer using these commands (potentially with some additional options enabled) in your scripts as they keep backward compatibility as much as possible.

How to safely and error-free use such commands in scripts?

Just use apt-get or apt-cache respectively instead of plain apt. :) See this answer for a list of equivalents.

Is there a way to only and only redirect STDOUT of apt show to a file?

You did that correctly already: >file or 1>file redirects stdout, 2>file redirects stderr and &>file redirects both to file.

AppStream System Cache – Fix Metadata Errors in Ubuntu 16.04

This requires a manual edit, due to a bug in a settings file for the fwupd package:

sudo apt install expat
xmlwf /var/cache/app-info/xmls/fwupd.xml
sudo vim /var/cache/app-info/xmls/fwupd.xml

Go to the line number given by xmlwf In my case I got

/var/cache/app-info/xmls/fwupd.xml:268:72: not well-formed (invalid token)

Replace the & character (on the line 268 in my case) with &

Then you can run update again:

sudo apt update

Best Answer

Related Solutions

APT – Resolving ‘Unstable CLI Interface’ Warning

AppStream System Cache – Fix Metadata Errors in Ubuntu 16.04

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