[Bug 1782567] Re: apt changelog outputs "usage: which [-as] program ..." if variable PAGER doesn't exist

[Paulo Marcel Coelho Aragão]

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

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https://bugs.launchpad.net/bugs/1782567

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

Status in apt package in Ubuntu:
  Invalid

Bug description:
  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)

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