This question explains how to find out if a given Debian package has been installed, but it does not take into account "synonyms" when installing via apt-get.

For instance, if I try apt-get install libncurses-dev, apt-get replies:

Note, selecting 'libncurses5-dev' instead of 'libncurses-dev'

And then it installs that package (libncurses5-dev), which is fine by me.

But what if I want to make a script to detect if the package has already been installed?

dpkg -s libncurses-dev replies that the package is not installed, which is indeed correct, since it's libncurses5-dev that was installed. But I'd like my script to detect that, in this case, it no longer needs to install libncurses-dev.

I could not find an option in apt-get to check if the given package or one of its providers has already been installed, such that my script would work when checking for libncurses-dev as well as for libncurses5-dev.


If you want to write a script to check to see if package libncurses-dev or its alias has been installed, consider the following program flow:

  1. Check if the package has been installed with dpkg using the exact name, libncurses-dev in this case.
  2. If the above does not evaluate to true, then search apt for the package you are looking for using the non-aliased name:

    $ apt-cache search libncurses-dev
    libncurses5-dev - developer's libraries for ncurses

It appears that apt-cache search will return the 'alias' if the package has one.

  1. If #1 evaluates false and #2 returns an alias, just grab the package's alias and try #1 again.

Check dpkg again with the alias name of the package, in this case it would be libncurses5-dev. If dpkg does not find the package by an alias (actually a superseded package) then it must not be installed.

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  • Thanks, but on my machine I had to use apt-cache search, since apt-get search resulted in E: Invalid operation search. Is it a typo, or does your apt-get include the search operation? – anol Jun 25 '15 at 17:13
  • @anol Ah yes, it was indeed a typo, thanks for catching that. – 111--- Jun 25 '15 at 17:39
  • There's just a minor issue I had: even after removing the package (including via purge), apt-cache still lists it. And unlike dpkg, it doesn't include a status letter (such as i for installed), so I guess it would be necessary to use apt-cache search for the synonym, then dpkg to check if it's installed... a bit more complex than I expected, but still doable. Could you please confirm if all of that is required, or if you see a simpler way? – anol Jun 25 '15 at 21:03
  • Perhaps i was unclear, use dpkg to see if the package is installed on your system, this is always at step 1. Use apt-cache search only to generate the alias to use when rechecking via dpkg. apt-cache will not reflect installed packages, so it is unaffected if you purge a package, I would only use this to find aliases to check in dpkg. – 111--- Jun 25 '15 at 21:09

This looks like a job for an aptitude search.

$ aptitude -F %p search '~Plibncurses-dev'
$ aptitude -F %p search '~Plibncurses-dev ~rnative'
$ aptitude -F %p search '~Plibncurses-dev ~rnative ~i'

That last one would print nothing if libncurses5-dev wasn't installed.

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  • Can I expect aptitude to be as widely available as apt-cache on a given machine? I mean, would there be potential users who might have one installed but not the other? – anol Jun 26 '15 at 5:12
  • 1
    @anol No, aptitude isn't as common. apt-cache is part of the base installation (it's in the apt package), aptitude is a separate package that isn't always installed. – Gilles 'SO- stop being evil' Jun 26 '15 at 8:26

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