apt changelog outputs "usage: which [-as] program ..." if variable PAGER doesn't exist

[Paulo Marcel Coelho Aragão]

When variable PAGER isn't in the environment, apt changelog always outputs this message:

usage: which [-as] program ...

but it goes on and shows the changelog with less. Most certainly it's running:

which $PAGER

without checking first if PAGER is empty.

sensible-browser has the same bug, but with variable BROWSER:

bug #1782447

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: apt 1.6.3
ProcVersionSignature: Ubuntu 4.15.0-29.31-generic 4.15.18
Uname: Linux 4.15.0-29-generic x86_64
ApportVersion: 2.20.9-0ubuntu7.2
Architecture: amd64
CurrentDesktop: XFCE
Date: Thu Jul 19 09:35:46 2018
InstallationDate: Installed on 2018-04-28 (81 days ago)
InstallationMedia: Xubuntu 18.04 LTS "Bionic Beaver" - Release amd64 (20180426)
SourcePackage: apt
UpgradeStatus: No upgrade log present (probably fresh install)

[Julian Andres Klode (juliank)]

Cannot reproduce. APT does not run which, so it's definitely not apts problems.

[Paulo Marcel Coelho Aragão (marcelpaulo)]

The bug was present in 1.6.3, but it seems to have been fixed in 1.6.3ubuntu0.1.

If you roll back to 1.6.3, it's easy to reproduce it:

$ PAGER=
$ apt changelog apt

It shows this error message:

usage: which [-as] program ...

and then goes on to show the changelog for apt.

Whether apt called which or not, it was a bug nonetheless. The changelog for apt doesn't mention fixing this, but it has been fixed because it cannot be reproduced on 1.6.3ubuntu0.1

[Julian Andres Klode (juliank)]

There is no difference there between 1.6.3 and 1.6.3ubuntu0.1, the latter being a security update for the mirror:// method.