Hcfyk

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).

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.

...

Guessing you need to handle the number of available updates, here is a suggestion:

# With no option, returns two numbers, no CR nor LF

/usr/lib/update-notifier/apt-check



# With --human-readable, returns numbers, locale LANG text & CR/LF

/usr/lib/update-notifier/apt-check  --human-readable

No need to sudo

The output is easy to work with

More options:

> /usr/lib/update-notifier/apt-check  --help

Usage: apt-check [options]



Options:

  -h, --help            show this help message and exit

  -p, --package-names   Show the packages that are going to be

                        installed/upgraded

  --human-readable      Show human readable output on stdout

  --security-updates-unattended

                        Return the time in days when security updates are

                        installed unattended (0 means disabled)

From man 8 apt:

... enables some options ...

Then I went through /usr/share/doc/apt/examples/configure-index.gz (using zcat(1) to show text content) and noticed this option:

apt::cmd::show-update-stats

So I worked out the following command that did exactly what I wanted:

# apt-get -o apt::cmd::show-update-stats=true update

Tested to be working on Xenial and Bionic.