How to check from bash if package exists in Debian

Question

I would like to write an installation bash script, where I would like to install MySQL server.

On Linux Mint I had followed code:

apt-get -y --force-yes install mysql-server-5.6

but I installed the new Debian 8 and there is no mysql-server - instead there is mariadb.

How can I find out if package exists?

I just know that there is dpkg -s which should tell whether a package is installed.

Answer 1

(the below is from Ubuntu, but the same technique obviously works on Debian as well)

$ apt-cache show screen
Package: screen
Priority: optional
Section: misc
Installed-Size: 950
Maintainer: Ubuntu Developers <[email protected]>
Original-Maintainer: Axel Beckert <[email protected]>
Architecture: amd64
Version: 4.1.0~20120320gitdb59704-9
Depends: libc6 (>= 2.15), libpam0g (>= 0.99.7.1), libtinfo5
Suggests: iselect (>= 1.4.0-1) | screenie | byobu
Filename: pool/main/s/screen/screen_4.1.0~20120320gitdb59704-9_amd64.deb
Size: 645730
...

If the package exists, information will be displayed. If not, you'll see something like:

$ apt-cache show foobar
N: Unable to locate package foobar
E: No packages found

Additionally, the exit code of apt-cache will be non-zero if no matching packages are found.

Additional note: If you're using apt-cache show package where package is a virtual one (one that doesn't exist, but is, for example, referenced by other packages), you'll get:

N: Can't select versions from package 'package' as it is purely virtual
N: No packages found

The exit code of this is zero (which is a bit misleading in my opinion.)

Answer 2

I would use dpkg -l mysql-server &> /dev/null && echo "mysql-server is installed".

It will check if the mysql-server package is installed and if so, it prints this fact to the screen. A more sophisticated solution would be, in bash (untested):

function package_exists() {
    return dpkg -l "$1" &> /dev/null
}

So one can do in a script:

if ! package_exists mysql-server ; then
    echo ”Please install mysql-server!"
fi

Answer 3

In a one-liner:

apt-cache pkgnames | grep -q "\<$your_package_name\>"

exits with 0 if it's present, 1 if not.

Bonus: efficient check for multiple packages, listed in file "packages_we_want", one per line, sorted with sort:

apt-cache --no-generate pkgnames | sort | comm -13 - packages_we_want lists all packages that you want, but do not exist in the repositories.

apt-cache --no-generate pkgnames | sort | comm -12 - packages_we_want lists all packages that you want and exist in the repositories.

Answer 4

My solution 😎

function package_exists() {
    dpkg -s "$1" &> /dev/null
    return $?
}

if package_exists abra; then
    CLIENT=abra
elif package_exists cadabra; then
    CLIENT=cadabra
else
     echo 'Client not found!'
     exit 1
fi