.deb files are regular ar archives. You can manipulate the file by using ar command.

For example, I have a package called lynx_2.8.8dev.15-2_all.deb.

To extract the file, just run ar x <.deb.filename>. For example:

ar x lynx_2.8.8dev.15-2_all.deb

You will see 3 files being extracted, control.tar.gz, data.tar.gz and debian binary.

ls

returns:

control.tar.gz  data.tar.gz  debian-binary  lynx_2.8.8dev.15-2_all.deb

debian-binary is a text file containing deb packaging version number.

cat debian-binary 
 
2.0

control.tar.gz contained control, preinst and md5sums.

tar -tf control.tar.gz ./
 
./md5sums
./control
./preinst

data.tar.gz is a compressed file containing the files which are going to be installed on the system.

tar -tf data.tar.gz ./
 
./usr/
./usr/share/
./usr/share/doc/
./usr/share/doc/lynx/
./usr/share/doc/lynx/copyright
./usr/share/doc/lynx/changelog.Debian.gz