The marked answer has the problem that the available packages on the machine that is doing the downloads might be different from the target machine, and thus the package set might be incomplete.
To avoid this and get all dependencies, use the following:
Some packages returned from apt-rdepends don't exist with the exact name for apt-get download to download (for example, libc-dev). In those cases, filter out those exact names (be sure to use ^<NAME>$ so that other related names, for example libc-dev-bin, that do exist are not skipped).
I used apt-cache depends packageto get all required packages in any case if the are already installed on system or not.
So it will work always correct.
Because the command apt-cache works different, depending on language, you have to try this command on your system and adapt the command.
apt-cache depends yourpackage
On an englisch system you get:
And the german version with the term:
"Hängt ab von:"
You have to change the term "yourpackage" to your wish twice in this command, take care of this!
This text is used twice in this command, if you want to adapt it to your language take care of this!
$ sudo apt-get --print-uris --yes -d --reinstall install yourpackage $(apt-cache depends yourpackage | grep "Hängt ab von:" | sed 's/ Hängt ab von://' | sed ':a;N;$!ba;s/\n//g') | grep ^\' | cut -d\' -f2 >downloads.list
You get the list of links in downloads.list
Check the list, go to your folder and run the list:
$ cd yourpathToYourFolder
$ wget --input-file downloads.list
Somewhat simplified (and what worked for me) way that worked for me (based on all the above)
Note that dependencies hierarchy can go deeper then one level
This will download all the Debs to the current directory, and will NOT fail if It can't find a candidate.
Also does NOT require sudo to run sript!
nano getdebs.sh && chmod +x getdebs.sh && ./getdebs.sh
#!/bin/bash
package=ssmtp
apt-cache depends "$package" | grep Depends: >> deb.list
sed -i -e 's/[<>|:]//g' deb.list
sed -i -e 's/Depends//g' deb.list
sed -i -e 's/ //g' deb.list
filename="deb.list"
while read -r line
do
name="$line"
apt-get download "$name"
done < "$filename"
apt-get download "$package"
Note: I used this as my example because I was actually trying to DL the Deps for SSMTP and it failed on debconf-2.0, but this script got me what I need!
Make sure /path-to/directory/apt/cache and /path-to/directory/apt/lists exist.
If you don't set -o Dir::Cache it points to /var/cache/apt,
Dir::State::Lists points to /var/lib/apt/lists (which keeps the index files of available packages)
Both -o options can be used with update and upgrade instead of install.
On different machine run the same command without '-d'
IF you accept the caveat that there may be dependencies already installed on your system, then the easiest way is to go apt-get install --simulate <your_package>, this will first list all the deps it will install, then copy the list of packages, then apt-get download <the_list_of_packages>
e.g. for qt5-gtk2-platformtheme on a xubuntu-21.04 MINIMAL INSTALL you'll get (after apt-get install --simulate) the following: