Easily unpack deb, repack deb with new version

Question

I have already seen Easily unpack DEB, edit postinst, and repack DEB - however, that one doesn't explain how to properly change the .deb version number if I want to do some changes the original .deb file.

I'm on Ubuntu 14.04, and let's take hostapd for an example:

$ mkdir /tmp/debtest
$ cd /tmp/debtest/
$ apt-get download hostapd
Get:1 http://dk.archive.ubuntu.com/ubuntu/ trusty-updates/universe hostapd amd64 1:2.1-0ubuntu1.4 [423 kB]
Fetched 423 kB in 1s (361 kB/s)  
$ ls -la hostapd_1%3a2.1-0ubuntu1.4_amd64.deb 
-rw-rw-r-- 1 myuser myuser 422846 Nov 10  2015 hostapd_1%3a2.1-0ubuntu1.4_amd64.deb

Now we can unpack as in the cited link above:

$ mkdir unpack-hostapd
$ dpkg-deb -R hostapd_1%3a2.1-0ubuntu1.4_amd64.deb unpack-hostapd
$ ls -la unpack-hostapd/
total 20
drwxr-xr-x 5 myuser myuser 4096 Jan 26 11:31 .
drwxrwxr-x 3 myuser myuser 4096 Jan 26 11:31 ..
drwxr-xr-x 2 myuser myuser 4096 Nov  9  2015 DEBIAN
drwxr-xr-x 6 myuser myuser 4096 Nov  9  2015 etc
drwxr-xr-x 4 myuser myuser 4096 Nov  9  2015 usr

Let's say I want to make a trival change, say appending a line of text to README.Debian:

echo "Just a test line" >> unpack-hostapd/usr/share/doc/hostapd/README.Debian

... and now I want to repack this as a new .deb.

First question - is there a way to retrieve the current (old) version of the package from the unpacked state? Because I don't trust filenames, I'd usually do:

$ apt-cache policy hostapd
hostapd:
  Installed: (none)
  Candidate: 1:2.1-0ubuntu1.4
...

... and this tells me I've downloaded version 1:2.1-0ubuntu1.4 of the package when I used apt-get download... - but not necessarily what is the version inside the unpack-hostapd directory. Is there a command that will tell me the package version of the originating .deb that was unpacked into the unpack-hostapd directory?

Now, I've used debchange as dch -i before to auto-increment a version number (although in other source projects), but when I try it here:

$ cd unpack-hostapd
$ pwd
/tmp/debtest/unpack-hostapd
$ dch -e
dch: fatal error at line 580:
Cannot find debian/changelog anywhere!
Are you in the source code tree?
(You could use --create if you wish to create this file.)
$ find . -name 'changelog*'
./usr/share/doc/hostapd/changelog.Debian.gz
$ dpkg -c ../hostapd_1%3a2.1-0ubuntu1.4_amd64.deb | grep changelog
-rw-r--r-- root/root      2126 2015-11-09 14:56 ./usr/share/doc/hostapd/changelog.Debian.gz

... but, I cannot change any of that here.

So, my second question is: is there an easy way (like dch -i is for source packages) to change the .deb package version number, and possibly add a changelog, to an unpacked .deb package like this?

Of course, ultimately I'd like to re-pack this new version as a .deb package, for which the link above suggests something like dpkg-deb -b unpack-hostapd hostapd_1%3a2.1-0ubuntu1.4_amd64.deb; although, say here I'd rather use version 1:2.2, so I'd finally use a filename like dpkg-deb -b unpack-hostapd hostapd_1%3a2.2_amd64.deb - however, that version should also match what is recorded inside the .deb, and I don't know how to do that...

Answer 1

The version is defined in the binary control file, which is extracted in DEBIAN/control when using dpkg-deb -R. Look for a Version: field:

Version: 1:2.5.2+v2.4-3+b1

This is where you'd edit the version number for your new package. (You can optionally add a changelog entry to the changelog in usr/share/doc/hostapd/changelog.Debian.gz.) Then you can rebuild your package like this, so that dpkg-deb determines the correct file name for you:

mkdir newpkg
dpkg-deb -b hostapd newpkg

This will produce a new package in the newpkg directory, named appropriately.

Ideally you should check your new binaries' library requirements and update the dependency information in control too!

Answer 2

Here's what kind of manual edit worked for me - however, this was sort of a blind guess, so still nice to have an answer from someone who understands the system:

# decompress changelog.Debian.gz
unpack-hostapd$ gzip -d  usr/share/doc/hostapd/changelog.Debian.gz

# edit the uncompressed changelog.Debian:
# add this on top:
# wpa (2.2) trusty-security; urgency=medium
# 
# * whatever
# 
# wpa (2.1-0ubuntu1.4) trusty-security; urgency=medium
# ....
unpack-hostapd$ nano usr/share/doc/hostapd/changelog.Debian

# repack changelog.Debian.gz
unpack-hostapd$ gzip -9 usr/share/doc/hostapd/changelog.Debian

# change DEBIAN/control - Source: and Version:
# change to:
# Source: wpa (2.2)
# Version: 1:2.2
unpack-hostapd$ nano DEBIAN/control

# repack .deb:
unpack-hostapd$ cd ..
$ dpkg-deb -b unpack-hostapd hostapd_1%3a2.2_amd64.deb

# now can install the deb
sudo dpkg -i hostapd_1%3a2.2_amd64.deb