How can I check if a package is installed (no superuser privileges)?

apt-cache policy <package name>

I always just use this from the command line:

dpkg -l | grep mysql

so the above asks dpkg to list all the installed packages and then I grep for only those that have mysql in the name.

One more variant, using aptitude this time:

aptitude show <package>

Tab completion works here as well.

You can use dselect. It provides non-su read-only access.

Also, dpkg -s <package name> provides a lot of details related to a package. Eg"

userme:~$ dpkg-query -s sl
Package: sl
Status: unknown ok not-installed
Priority: optional
Section: games

You may use dpkg-query -s <package> 2>/dev/null | grep -q ^"Status: install ok installed"$ in scripts, since it returns exit code 1, if the <package> is not installed, and 0 if the <package> is installed.

dpkg-query --showformat='${db:Status-Status}'

This produces a small output string which is unlikely to change and is easy to compare deterministically without grep:

pkg=hello
status="$(dpkg-query -W --showformat='${db:Status-Status}' "$pkg" 2>&1)"
if [ ! $? = 0 ] || [ ! "$status" = installed ]; then
  sudo apt install $pkg
fi

The $? = 0 check is needed because if you've never installed a package before, and after you remove certain packages such as hello, dpkg-query exits with status 1 and outputs to stderr:

dpkg-query: no packages found matching hello

instead of outputting not-installed. The 2>&1 captures that error message too when it comes preventing it from going to the terminal.

For multiple packages:

pkgs='hello certbot'
install=false
for pkg in $pkgs; do
  status="$(dpkg-query -W --showformat='${db:Status-Status}' "$pkg" 2>&1)"
  if [ ! $? = 0 ] || [ ! "$status" = installed ]; then
    install=true
    break
  fi
done
if "$install"; then
  sudo apt install $pkgs
fi

The possible statuses are documented in man dpkg-query as:

   n = Not-installed
   c = Config-files
   H = Half-installed
   U = Unpacked
   F = Half-configured
   W = Triggers-awaiting
   t = Triggers-pending
   i = Installed

The single letter versions are obtainable with db:Status-Abbrev, but they come together with the action and error status, so you get 3 characters and would need to cut it.

So I think it is reliable enough to rely on the uncapitalized statuses (Config-files vs config-files) not changing instead.

dpkg -s exit status

This unfortunately doesn't do what most users want:

pkgs='qemu-user pandoc'
if ! dpkg -s $pkgs >/dev/null 2>&1; then
  sudo apt-get install $pkgs
fi

because for some packages, e.g. certbot, doing:

sudo apt install certbot
sudo apt remove certbot

leaves certbot in state config-files, which means that config files were left in the machine. And in that state, dpkg -s still returns 0, because the package metadata is still kept around so that those config files can be handled more nicely.

To actually make dpkg -s return 1 as desired, --purge would be needed:

sudo apt remove --purge certbot

which actually moves it into not-installed/dpkg-query: no packages found matching.

Note that only certain packages leave config files behind. A simpler package like hello goes directly from installed to not-installed without --purge.

Tested on Ubuntu 20.10.

Python apt package

There is a pre-installed Python 3 package called apt in Ubuntu 18.04 which exposes an Python apt interface!

A script that checks if a package is installed and installs it if not can be seen at: https://stackoverflow.com/questions/17537390/how-to-install-a-package-using-the-python-apt-api/17538002#17538002

Here is a copy for reference:

#!/usr/bin/env python
# aptinstall.py

import apt
import sys

pkg_name = "libjs-yui-doc"

cache = apt.cache.Cache()
cache.update()
cache.open()

pkg = cache[pkg_name]
if pkg.is_installed:
    print "{pkg_name} already installed".format(pkg_name=pkg_name)
else:
    pkg.mark_install()

    try:
        cache.commit()
    except Exception, arg:
        print >> sys.stderr, "Sorry, package installation failed [{err}]".format(err=str(arg))

Check if an executable is in PATH instead

See: https://stackoverflow.com/questions/592620/how-can-i-check-if-a-program-exists-from-a-bash-script/22589429#22589429

See also

• https://stackoverflow.com/questions/1298066/check-if-an-apt-get-package-is-installed-and-then-install-it-if-its-not-on-linu/54239534#54239534
• How do I check if a package is installed on my server?

Simpler solution:

There is now an apt list command that lists installed packages. You can also search for a specific package with

apt list <package>

See man apt for more information.

You need to check the status printed by dpkg -l, example :

$ dpkg -l firefox-esr vim winff
Desired=Unknown/Install/Remove/Purge/Hold
| Status=Not/Inst/Conf-files/Unpacked/halF-conf/Half-inst/trig-aWait/Trig-pend
|/ Err?=(none)/Reinst-required (Status,Err: uppercase=bad)
||/ Name                                 Version                 Architecture            Description
+++-====================================-=======================-=======================-=============================================================================
hi  firefox-esr                          52.9.0esr+build2-0ubunt amd64                   Safe and easy web browser from Mozilla
ii  vim                                  2:8.1.1198-0york0~14.04 amd64                   Vi IMproved - enhanced vi editor
rc  winff                                1.5.3-3                 all                     graphical video and audio batch converter using ffmpeg or avconv

Here both vim and firefox-esr are installed, therefore you can type :

$ dpkg -l firefox-esr | grep -q ^.i && echo This package is installed. || echo This package is NOT installed.
This package is installed.
$ dpkg -l vim | grep -q ^.i && echo This package is installed. || echo This package is NOT installed.
This package is installed.
$ dpkg -l winff | grep -q ^.i && echo This package is installed. || echo This package is NOT installed.
This package is NOT installed.

Example to use specific value as var in shell scripts (eg test.sh)

#!/bin/sh
PACKAGE="${1}"
INSTALLED=$(dpkg -l | grep ${PACKAGE} >/dev/null && echo "yes" || echo "no")

echo "${PACKAGE} is installed ... ${INSTALLED}"

Make it executable and go start with:

test.sh openssh-server

Or do whatever you want with in your scripts