I am using Ubuntu 20.04 and have a list of package names of which I want to check whether it is part of the default Ubuntu repository.

So far I am iterating over the list an check with the following script:

#!/bin/bash



input="modified_list.txt"



RED='033[0;31m'

NC='033[0m'



if [ ! -f $input ];

then

    echo -e "file does not exist: $input"

    exit 1

fi



while read -r line

do

    if [[ $(apt policy $line  2> /dev/null | grep 'focal' | wc -l) -gt 0 ]];

    then

        # print package name normal if part of ubuntu default repo

        echo -e "$line	"

    else

        # print package name red if not in default repo

        echo -e "${RED}${line}${NC}" 

    fi



done < $input

Here I noticed the package xvnc4viewer is (according to the script) not part of the repository. When executing apt policy xvnc4viewer the terminal outputs:

xvnc4viewer:

  Installed: 4.1.1+xorg4.3.0-37.3ubuntu2

  Candidate: 4.1.1+xorg4.3.0-37.3ubuntu2

  Version table:

 *** 4.1.1+xorg4.3.0-37.3ubuntu2 100

        100 /var/lib/dpkg/status

When using the command on other packages, I found an URL or something that helped me to figure out where the package comes from, but in this case I couldn't figure it out. Using apt-cache search xvnc4viewer the package is found but commands like apt-cache showpkg did not help me either. So, how do I figure out where the package is coming from?