Since Fedora 26, the Dnf repoquery subcommand supports has a new option for listing all user-installed packages:
$ dnf repoquery --qf '%{name}' --userinstalled \
| grep -v -- '-debuginfo$' \
| grep -v '^\(kernel-modules\|kernel\|kernel-core\|kernel-devel\)$' > pkgs_a.lst
In contrast to other methods, it also lists all debuginfo packages. The additional grep in the above example filters them out.
To install the list on host B:
$ < pkgs_a.lst xargs dnf -y install
Dnf API
With recent Dnf versions (e.g. Fedora >= 23), the package database can be queried for user installed package names via the Dnf Python API:
$ python3 -c 'import dnf; b = dnf.Base(); b.fill_sack(); \
l = sorted(set(x.name for x in b.iter_userinstalled() \
if not x.name.endswith("-debuginfo") \
and x.name not in \
["kernel-modules", "kernel", "kernel-core", "kernel-devel"] )); \
print("\n".join(l)) ' > pkgs_a.lst
# dnf install $(cat pkgs_a.lst) # on host_b
By default, dnf install aborts if one or more packages aren't available anymore. Alternatively, dnf can be forced to install all remaining ones:
# dnf install --setopt=strict=0 $(cat pkgs_a.lst) # on host_b
PS: Put the above code and more into user-installed.py that also supports other distributions.
history userinstalled
On Fedora 23 and later, Dnf provides the
# dnf history userinstalled
command that lists all user installed packages. As of 2016-11, its usefulness is limited because there is no way to control its output and it prints packages fully qualified (i.e. including version information).
userinstalled Limitations
Note that the marking of packages as user-installed has some limitations on some Fedora versions, for Fedora 23-ish era systems (from around 2015-11) the following issues are relevant):
Repoquery
On older Fedora systems, where Dnf, the Dnf API and dnf history userinstalled aren't available, one can use repoquery instead, e.g.:
$ repoquery --installed \
--qf '%{n} | %{yumdb_info.reason} | %{yumdb_info.installed_by}' --all \
| awk -F'|' ' $2 ~ /user/ && ($3 != 4294967295) { print $1 }' \
| sort -u > pkgs_a.lst
The second awk condition is used to exclude packages that were installed by the installer. The installer's user-id was apparently stored as 4294967295 - alternatively you can write something like ($3 == 0 || $3 == your-user-id).
Note that this command works on Fedora up to release 21 - but e.g. not on release 23, because the command repoquery was replaced with dnf repoquery. And dnf repoquery does not understand the %{yumdb_info.reason} tag.
Best Answer
You can actually remove and install packages in the same operation, with
dnf swap. And since the option takes groups as well as just single package names, you can switch one for another very simply: