This file documents things you should know to write a new debhelper program.
There are lots of debhelper commands. To make the learning curve shallower,
I want them all to behave in a standard manner:
All debhelper programs have names beginning with "dh_". This is so we don't
pollute the name space too much.
Debhelper programs should never output anything to standard output except
error messages, important warnings, and the actual commands they run that
modify files under debian/ and debian/tmp, etc (this last only if they are
passed -v, and if you output the commands, you should indent them with 1 tab).
This is so we don't have a lot of noise output when all the debhelper commands
in a debian/rules are run, so the important stuff is clearly visible.
Debhelper programs should accept the options, -v, -i, -a, -p, --no-act, and
-P, and any long forms of these options, like --verbose . If necessary, the
options may be ignored.
If debhelper commands need config files, they should use
debian/package.filename as the name of the config file (replace filename
with whatever your command wants), and debian/filename should also be
checked for config information for the first binary package in
debian/control. Also, debhelper commands should accept the same sort of
information that appears in the config files, on their command lines, if
possible, and apply that information to the first package they act on.
Debhelper programs should never modify the debian/postinst, debian/prerm,
etc scripts, instead, they can add lines to debian/postinst.debhelper, etc.
The autoscript() function (see below) is one easy way to do this.
dh_installdeb is an exception, it will run after the other commands and
merge these modifications into the actual postinst scripts.
There are always exceptions. Just ask me.
All debhelper programs use the dh_lib library (actually it's a shell script)
to parse their arguments and set some useful variables. It's not mandatory
that your program use dh_lib, but it will make it a lot easier to keep it in
sync with the rest of debhelper if it does, so this is highly encouraged.
Typically, you invoke dh_lib like this:
The path statement is there to make your program look first in debian/ for
dh_lib (so users can install a modified version there if necessary), then the
rest of the path, then the canonical location of dh_lib, /usr/lib/debhelper.
All debhelper programs should respond to certain arguments, such as -v, -i,
-a, and -p. To help you make this work right, dh_lib handles argument
As soon as dh_lib loads, it processes any arguments that have been passed to
your program. The following variables may be set during this stage; your
program can use them later:
switch variable description
-v DH_VERBOSE should the program verbosely output what it is
--no-act DH_NO_ACT should the program not actually do anything?
-i,-a,-p DH_DOPACKAGES a space delimited list of the binary packages
to act on
-i,-p DH_DOINDEP a space delimited list of the binary independent
packages to act on
-a,-p DH_DOARCH a space delimited list of the binary dependent
packages to act on
-n DH_NOSCRIPTS if set, do not make any modifications to the
package's postinst, postrm, etc scripts.
-X DH_EXCLUDE exclude a something from processing (you
decide what this means for your program)
DH_EXCLUDE_GREP same as DH_EXCLUDE, except all items are
separated by '|' characters, instead of spaces,
handy for egrep -v
include conffiles. It's -x for obscure
-d DH_D_FLAG you decide what this means to your program
-r DH_R_FLAG you decide what this means to your program
-k DH_K_FLAG you decide what this means to your program
-P DH_TMPDIR package build directory (implies only one
package is being acted on)
-u DH_U_PARAMS will be set to a string, that is typically
parameters your program passes on to some
-m DH_M_PARAMS will be set to a string, you decide what it
means to your program
-V DH_V_FLAG will be set to a string, you decide what it
means to your program
-V DH_V_FLAG_SET will be 1 if -V was specified, even if no
parameters were passed along with the -V
-A DH_PARAMS_ALL generally means that additional command line
parameters passed to the program (other than
those processed here), will apply to all
binary packages the program acts on, not just
--init-script DH_INIT_SCRIPT will be set to a string, which specifies an
init script name (probably only
dh_installinit will ever use this)
Any additional command line parameters that do not start with "-" will be
ignored, and you can access them later just as you normally would ($1, $2,
If you need a new command line option, just ask me, and I will add it.
The following variables are also set, you can use any of them:
MAINPACKAGE the name of the first binary package listed in
DH_FIRSTPACKAGE the first package we were instructed to act on. This package
typically gets special treatment, additional arguments
specified on the command line may effect it.
Dh_lib also contains a number of functions you may find useful.
Pass this function a string that is a shell command. It will run the
command (unless DH_NO_ACT is set), and if DH_VERBOSE is set, it will
also output the command to stdout. You should use this function for
almost all commands your program performs that manipulate files in
the package build directories.
This is the same as doit(), except you can pass more complicated
commands to it (ie, commands involving piping redirection)
Pass this command a string, and it will echo it if DH_VERBOSE is set.
Pass this command a string, it will output it to standard error and
Pass this command a string, and it will output it to standard error
as a warning message.
Pass this command the name of a binary package, it will return the
name of the tmp directory that will be used as this package's
package build directory. Typically, this will be "debian/tmp" or
Pass this command the name of a binary package, and the base name of a
file, and it will return the actual filename to use. This is used
for allowing debhelper programs to have configuration files in the
debian/ directory, so there can be one config file per binary
package. The convention is that the files are named
debian/package.filename, and debian/filename is also allowable for
the MAINPACKAGE. If the file does not exist, nothing is returned.
Pass this command the name of a binary package, and it will return
the name to prefix to files in debian/ for this package. For the
MAINPACKAGE, it returns nothing (there is no prefix), for the other
packages, it returns "package.".
Pass this command the name of a package, it returns 1 if the package
is a native debian package.
As a side effect, VERSION is set to the version number of the
Pass 3 parameters:
1: script to add to
2: filename of snippet
3: sed commands to run on the snippet. Ie, s/#PACKAGE#/$PACKAGE/
This command automatically adds shell script snippets to a debian
maintainer script (like the postinst or prerm).
Dh_lib is still evolving.
There will probably be a perl version too, in the future.
-- Joey Hess <email@example.com>