Trjtdtk

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.