=encoding UTF-8

=head1 NAME

debhelper - the debhelper tool suite

=head1 SYNOPSIS

B<dh_>I<*> [B<-v>] [B<-a>] [B<-i>] [B<--no-act>] [B<-p>I<package>] [B<-N>I<package>] [B<-P>I<tmpdir>]

=head1 DESCRIPTION

Debhelper is used to help you build a Debian package. The philosophy behind
debhelper is to provide a collection of small, simple, and easily
understood tools that are used in F<debian/rules> to automate various common
aspects of building a package. This means less work for you, the packager.
It also, to some degree means that these tools can be changed if Debian
policy changes, and packages that use them will require only a rebuild to
comply with the new policy.

A typical F<debian/rules> file that uses debhelper will call several debhelper
commands in sequence, or use L<dh(1)> to automate this process. Examples of
rules files that use debhelper are in F</usr/share/doc/debhelper/examples/>

To create a new Debian package using debhelper, you can just copy one of
the sample rules files and edit it by hand. Or you can try the B<dh-make>
package, which contains a L<dh_make|dh_make(1)> command that partially
automates the process. For a more gentle introduction, the B<maint-guide> Debian 
package contains a tutorial about making your first package using debhelper.

Except where the tool explicitly denotes otherwise, all of the debhelper
tools assume that they run from the root directory of an unpacked source
package.  This is so they can locate files like F<debian/control>
when needed.

=head1 DEBHELPER COMMANDS

Here is the list of debhelper commands you can use. See their man
pages for additional documentation.

=over 4

#LIST#

=back

=head2 Deprecated Commands

A few debhelper commands are deprecated and should not be used.

=over 4

#LIST_DEPRECATED#

=back

=head2 Other Commands

If a program's name starts with B<dh_>, and the program is not on the above
lists, then it is not part of the debhelper package, but it should still
work like the other programs described on this page.

=head1 DEBHELPER CONFIG FILES

Many debhelper commands make use of files in F<debian/> to control what they
do. Besides the common F<debian/changelog> and F<debian/control>, which are
in all packages, not just those using debhelper, some additional files can
be used to configure the behavior of specific debhelper commands. These
files are typically named debian/I<package>.foo (where I<package> of course,
is replaced with the package that is being acted on).

For example, B<dh_installdocs> uses files named F<debian/package.docs> to list
the documentation files it will install. See the man pages of individual
commands for details about the names and formats of the files they use.
Generally, these files will list files to act on, one file per line. Some
programs in debhelper use pairs of files and destinations or slightly more
complicated formats.

Note if there is only one binary package listed in F<debian/control>, then
debhelper will use F<debian/foo> when there's no F<debian/I<package>.foo> file.
In compat levels before compat 15, this fallback also occurs for the first
binary package listed in F<debian/control> when there are multiple binary
packages. However, it is often a good idea to keep the F<I<package>.> prefix
as it is more explicit and also required when upgrading to compat 15.

Additionally, there are some special cases where debhelper will always
fallback to a prefix-less version.  These are cases such as F<debian/copyright>
and F<debian/changelog>, where the files are generally used and needed for all
binary packages.

In some rare cases, you may want to have different versions of these files
for different architectures or OSes. If files named debian/I<package>.foo.I<ARCH>
or debian/I<package>.foo.I<OS> exist, where I<ARCH> and I<OS> are the same as the
output of "B<dpkg-architecture -qDEB_HOST_ARCH>" /
"B<dpkg-architecture -qDEB_HOST_ARCH_OS>",
then they will be used in preference to other, more general files.

Mostly, these config files are used to specify lists of various types of
files. Documentation or example files to install, files to move, and so on.
When appropriate, in cases like these, you can use standard shell wildcard
characters (B<?> and B<*> and B<[>I<..>B<]> character classes) in the files.
You can also put comments in these files; lines beginning with B<#> are
ignored.

The syntax of these files is intentionally kept very simple to make them
easy to read, understand, and modify.

=head2 Substitutions in debhelper config files

In compatibility level 13 and later, it is possible to use simple
substitutions in debhelper config files for the following tools:

=over 4

=item *

dh_clean

=item *

dh_install

=item *

dh_installcatalogs

=item *

dh_installdeb

=item *

dh_installdirs

=item *

dh_installdocs

=item *

dh_installexamples

=item *

dh_installinfo

=item *

dh_installman

=item *

dh_installwm

=item *

dh_link

=item *

dh_missing

=item *

dh_ucf

=back

All substitution variables are of the form I<${foo}> and the braces
are mandatory.  Variable names are case-sensitive and consist of
alphanumerics (a-zA-Z0-9), hyphens (-), underscores (_), and colons (:).
The first character must be an alphanumeric.

If you need a literal dollar sign that cannot trigger a substitution,
you can either use the B<${Dollar}> substitution or the sequence B<${}>.

The following expansions are available:

=over 4

=item B<DEB_HOST_*>, B<DEB_BUILD_*>, B<DEB_TARGET_*>

Expands to the relevant L<dpkg-architecture(1)> value (similar to
I<dpkg-architecture -qVARIABLE_HERE>).

When in doubt, the B<DEB_HOST_*> variant is the one that will work both
for native and cross builds.

For performance reasons, debhelper will attempt to resolve these
names from the environment first before consulting
L<dpkg-architecture(1)>.  This is mostly mentioned for completeness
as it will not matter for most cases.

=item B<Dollar>

Expands to a single literal B<$>-symbol.  This symbol will I<never>
be considered part of a substitution variable.  That is:

   # Triggers an error
   ${NO_SUCH_TOKEN}
   # Expands to the literal value "${NO_SUCH_TOKEN}"
   ${Dollar}{NO_SUCH_TOKEN}

This variable equivalent to the sequence B<${}> and the two can be
used interchangeably.

=item B<Newline>, B<Space>, B<Tab>

Expands to a single ASCII newline, space and tab respectively.

This can be useful if you need to include a literal whitespace
character (e.g. space) where it would otherwise be stripped or
used as a separator.

=item B<< env:I<NAME> >>

Expands to the environment variable I<NAME>.  The environment
variable must be set (but can be set to the empty string).

=back

Note that all variables must expand to a defined value.  As an example,
if debhelper sees I<${env:FOO}>, then it will insist that the environment
variable I<FOO> is set (it can be set to the empty string).

=head3 Substitution limits

To avoid infinite loops and resource exhaustion, debhelper will stop
with an error if the token contains many substitution variables (50) or
the total size of the expanded value exceed a certain size (4096
characters or 3x length of the original input - whichever is bigger).

Note the limit is per token. Every helper decides its own definition
of a token. The common case of files like F<< debian/I<package>.install >>,
each token is a file/path name.

=head3 Substitution limitations: filtering

The built-in substitution cannot be used to "filter" out content. Attempts
to create "comments" or "empty lines" via substitution will result in those
variables being considered a token in its own right with the content given.

If you want filtering, consider using an executable debhelper config file
with B<dh-exec> as interpreter. The B<dh-exec> tool supports several
features out of the box. Though keep in mind that B<dh-exec> has its own
substitution logic that can feature interact with the one from debhelper.

=head2 Executable debhelper config files

If you need additional flexibility, many of the debhelper tools
(e.g. L<dh_install(1)>) support executing a config file as a script.

To use this feature, simply mark the config file as executable
(e.g. B<< chmod +x debian/I<package>.install >>) and the tool will
attempt to execute it and use the output of the script.  In many
cases, you can use L<dh-exec(1)> as interpreter of the config file to
retain most of the original syntax while getting the additional
flexibility you need.


When using executable debhelper config files, please be aware of the
following:

=over 4

=item *

The executable config file B<must> exit with success (i.e. its return
code should indicate success).

=item *

In compatibility level 13+, the output will be subject to substitutions
(see L</Substitutions in debhelper config files>) where the tool
support these.  Remember to be careful if your generator I<also> provides
substitutions as this can cause unnecessary confusion. Notably, the
commonly used B<dh-exec> tool has its own substitution support.

Otherwise, the output will be used exactly as-is.  Notably, debhelper
will I<not> expand wildcards or strip comments or strip whitespace
in the output it reads. The B<dh-exec> tool has an output filter on
by default that will prune these things out.

=back

If you need the package to build on a file system where you cannot
disable the executable bit, then you can use L<dh-exec(1)> and its
B<strip-output> script.

=head1 SHARED DEBHELPER OPTIONS

The following command line options are supported by all debhelper programs.

=over 4

=item B<-v>, B<--verbose>

Verbose mode: show commands that modify the package build directory.

Note that verbose mode may also output other "internal" commands that do not
directly affect the package build directory.

=item B<--no-act>

Do not really do anything. If used with -v, the result is that the command
will output what it would have done.

=item B<-a>, B<--arch>

Act on architecture dependent packages that should be built for the
B<DEB_HOST_ARCH> architecture.

=item B<-i>, B<--indep>

Act on all architecture independent packages.

=item B<-p>I<package>, B<--package=>I<package>

Act on the package named I<package>. This option may be specified multiple
times to make debhelper operate on a given set of packages.

=item B<-s>, B<--same-arch>

Deprecated alias of B<-a>.

This option is removed in compat 12.

=item B<-N>I<package>, B<--no-package=>I<package>

Do not act on the specified package even if an B<-a>, B<-i>, or B<-p> option lists
the package as one that should be acted on.

=item B<--remaining-packages>

Do not act on the packages which have already been acted on by this debhelper
command earlier (i.e. if the command is present in the package debhelper log).
For example, if you need to call the command with special options only for a
couple of binary packages, pass this option to the last call of the command to
process the rest of packages with default settings. 

=item B<-P>I<tmpdir>, B<--tmpdir=>I<tmpdir>

Use I<tmpdir> for package build directory. The default is debian/I<package>

=item B<--mainpackage=>I<package>

B<Deprecated>: This option has no practical use in compat 15 or later as the
behaviour it affects is removed in compat 15.

This little-used option changes the package which debhelper considers the
"main package", that is, the first one listed in F<debian/control>, and the
one for which F<debian/foo> files can be used instead of the usual
F<debian/package.foo> files.

=item B<-O=>I<option>|I<bundle>

This is used by L<dh(1)> when passing user-specified options to all the
commands it runs. If the command supports the specified option or option
bundle, it will take effect. If the command does not support the option (or
any part of an option bundle), it will be ignored.

=back

=head1 COMMON DEBHELPER OPTIONS

The following command line options are supported by some debhelper programs.
See the man page of each program for a complete explanation of what each
option does.

=over 4

=item B<-n>

Do not modify F<postinst>, F<postrm>, etc. scripts.

=item B<-X>I<item>, B<--exclude=>I<item>

Exclude an item from processing. This option may be used multiple times,
to exclude more than one thing. The I<item> is typically part of a
filename, and any file containing the specified text will be excluded.

=item B<-A>, B<--all>

Makes files or other items that are specified on the command line take effect
in ALL packages acted on, not just the first.

=back

=head1 BUILD SYSTEM OPTIONS

The following command line options are supported by all of the B<dh_auto_>I<*>
debhelper programs. These programs support a variety of build systems,
and normally heuristically determine which to use, and how to use them.
You can use these command line options to override the default behavior.
Typically these are passed to L<dh(1)>, which then passes them to all the 
B<dh_auto_>I<*> programs.

=over 4

=item B<-S>I<buildsystem>, B<--buildsystem=>I<buildsystem>

Force use of the specified I<buildsystem>, instead of trying to auto-select
one which might be applicable for the package.

Pass B<none> as I<buildsystem> to disable auto-selection.

=item B<-D>I<directory>, B<--sourcedir=>I<directory>, B<--sourcedirectory=>I<directory>

Assume that the original package source tree is at the specified
I<directory> rather than the top level directory of the Debian
source package tree.

B<Warning>: The B<--sourcedir> variant matches a similar named option in
B<dh_install> and B<dh_missing> (etc.) for historical reasons.  While they
have a similar name, they have very distinct purposes and in some cases
it can cause errors when this variant is passed to B<dh> (when then passes
it on to all tools).

=item B<-B>[I<directory>], B<--builddir>[I<=directory>], B<--builddirectory>[I<=directory>]

Enable out of source building and use the specified I<directory> as the build
directory. If I<directory> parameter is omitted, a default build directory
will be chosen.

If this option is not specified, building will be done in source by default
unless the build system requires or prefers out of source tree building.
In such a case, the default build directory will be used even if
B<--builddirectory> is not specified.

If the build system prefers out of source tree building but still
allows in source building, the latter can be re-enabled by passing a build
directory path that is the same as the source directory path.

=item B<--parallel>, B<--no-parallel>

Control whether parallel builds should be used if underlying build
system supports them.  The number of parallel jobs is controlled by
the B<DEB_BUILD_OPTIONS> environment variable (L<Debian Policy,
section 4.9.1>) at build time. It might also be subject to a build
system specific limit.

If neither option is specified, debhelper currently defaults to
B<--parallel> in compat 10 (or later) and B<--no-parallel> otherwise.

As an optimization, B<dh> will try to avoid passing these options to
subprocesses, if they are unnecessary and the only options passed.
Notably this happens when B<DEB_BUILD_OPTIONS> does not have a
I<parallel> parameter (or its value is 1).

=item B<--max-parallel=>I<maximum>

This option implies B<--parallel> and allows further limiting the number of
jobs that can be used in a parallel build. If the package build is known to
only work with certain levels of concurrency, you can set this to the maximum
level that is known to work, or that you wish to support.

Notably, setting the maximum to 1 is effectively the same as using
B<--no-parallel>.

=item B<--reload-all-buildenv-variables>

By default, L<dh(1)> will compute several environment variables (e.g. by
using L<dpkg-buildflags(1)>) and cache them to avoid having all B<dh_auto_*>
tool recompute them.

When passing this option, the concrete B<dh_auto_*> tool will ignore
the cache from L<dh(1)> and retrigger a rebuild of these variables.
This is useful in the very rare case where the package need to do
multiple builds but with different B<...FLAGS> options.  A concrete
example would be needing to change the B<-O> parameter in B<CFLAGS> in
the second build:

    export DEB_CFLAGS_MAINT_APPEND=-O3

    %:
        dh $@

    override_dh_auto_configure:
        dh_auto_configure -Bbuild-deb ...
        DEB_CFLAGS_MAINT_APPEND=-Os dh_auto_configure \
           --reload-all-buildenv-variables -Bbuild-udeb ...

Without B<--reload-all-buildenv-variables> in the second call to
L<dh_auto_configure(1)>, the change in B<DEB_CFLAGS_MAINT_APPEND>
would be ignored as L<dh_auto_configure(1)> would use the cached value
of B<CFLAGS> set by L<dh(1)>.

This option is only available with B<< debhelper (>= 12.7~) >> when
the package uses compatibility level 9 or later.

=item B<--list>, B<-l>

List all build systems supported by debhelper on this system. The list
includes both default and third party build systems (marked as such). Also
shows which build system would be automatically selected, or which one
is manually specified with the B<--buildsystem> option.

=back

=head1 COMPATIBILITY LEVELS

From time to time, major non-backwards-compatible changes need to be made
to debhelper, to keep it clean and well-designed as needs change and its
author gains more experience. To prevent such major changes from breaking
existing packages, the concept of debhelper compatibility levels was
introduced. You must tell debhelper which compatibility level it should use, and
it modifies its behavior in various ways.

In current debhelper, you can specify the compatibility level in
F<debian/control> by adding a Build-Depends on the debhelper-compat package.
For example, to use v#RECOMMENDED_COMPAT# mode, ensure F<debian/control> has:

  Build-Depends: debhelper-compat (= #RECOMMENDED_COMPAT#)

This also serves as an appropriate versioned build dependency on a sufficient
version of the debhelper package, so you do not need to specify a separate
versioned build dependency on the debhelper package unless you need a specific
point release of debhelper (such as for the introduction of a new feature or
bugfix within a compatibility level).

Note that debhelper does not provide debhelper-compat for experimental or beta
compatibility levels; packages experimenting with those compatibility levels
should put the compat level in the B<X-DH-Compat> field of the B<Source> stanza
of the F<debian/control> file (or, if only for selected commands, the
B<DH_COMPAT> environment variable).

Historically, debhelper required specifying the compatibility level in the
file F<debian/compat>, and debhelper up to version 14 supports this for backward
compatibility. To use this method, the F<debian/compat> file should contain
the compatibility level as a single number, and no other content. If you
specify the compatibility level by this method, your package will also need a
versioned build dependency on a version of the debhelper package equal to (or
greater than) the compatibility level your package uses. So, if you specify
compatibility level #RECOMMENDED_COMPAT# in F<debian/compat>, ensure
F<debian/control> has:

  Build-Depends: debhelper (>= #RECOMMENDED_COMPAT#~)

Note that you must use exactly one method for specifying the default debhelper
compat level of the package. Whenever possible, the debhelper-compat
build-dependency is recommended.

If needed be, the B<DH_COMPAT> environment variable can be used to override
the compat level for a given command.  The feature is mostly useful for
either temporarily upgrading a few commands to a new compat level or
keeping a few commands on a lower compat level.  The feature is best used
sparingly as it effectively introduces special-cases into the
F<debian/rules> file that may be surprising to maintainers or reviewers
(or, in the long term, to yourself).

Unless otherwise indicated, all debhelper documentation assumes that you
are using the most recent compatibility level, and in most cases does not
indicate if the behavior is different in an earlier compatibility level, so
if you are not using the most recent compatibility level, you're advised to
read below for notes about what is different in earlier compatibility
levels.

=head2 Supported compatibility levels

The list of supported compatibility levels and the related upgrade check
list has moved to L<debhelper-compat-upgrade-checklist(7)>.

=head1 NOTES

=head2 Multiple binary package support

If your source package generates more than one binary package, debhelper
programs will default to acting on all binary packages when run. If your
source package happens to generate one architecture dependent package, and
another architecture independent package, this is not the correct behavior,
because you need to generate the architecture dependent packages in the
binary-arch F<debian/rules> target, and the architecture independent packages
in the binary-indep F<debian/rules> target.

To facilitate this, as well as give you more control over which packages
are acted on by debhelper programs, all debhelper programs accept the
B<-a>, B<-i>, B<-p>, and B<-s> parameters. These parameters are cumulative. 
If none are given, debhelper programs default to acting on all packages listed
in the control file, with the exceptions below.

First, any package whose B<Architecture> field in B<debian/control> does not
match the B<DEB_HOST_ARCH> architecture will be excluded
(L<Debian Policy, section 5.6.8>).

Also, some additional packages may be excluded based on the contents of the
B<DEB_BUILD_PROFILES> environment variable and B<Build-Profiles> fields in
binary package stanzas in B<debian/control>, according to the draft policy at
L<https://wiki.debian.org/BuildProfileSpec>.

=head3 Interaction between package selections and Build-Profiles

Build-Profiles affect which packages are included in the package
selections mechanisms in debhelper.  Generally, the package selections
are described from the assumption that all packages are enabled.  This
section describes how the selections react when a package is disabled
due to the active Build-Profiles (or lack of active Build-Profiles).

=over 4

=item -a/--arch, -i/--indep OR no selection options (a raw "dh_X" call)

The package disabled by Build-Profiles is silently excluded from the
selection.

Note you will receive a warning if I<all> packages related to these
selections are disabled.  In that case, it generally does not make
sense to do the build in the first place.

=item -N I<package> / --no-package I<package>

The option is accepted and effectively does nothing.

=item -p I<package> / --package I<package>

The option is accepted, but debhelper will not act on the package.

=back

Note that it does not matter whether a package is enabled or disabled
by default.

=head2 Automatic generation of Debian install scripts

Some debhelper commands will automatically generate parts of Debian
maintainer scripts. If you want these automatically generated things
included in your existing Debian maintainer scripts, then you need to add
B<#DEBHELPER#> to your scripts, in the place the code should be added.
B<#DEBHELPER#> will be replaced by any auto-generated code when you run
B<dh_installdeb>.

If a script does not exist at all and debhelper needs to add something to
it, then debhelper will create the complete script.

When inserting the B<#DEBHELPER#> token into a script, consider whether
any of the hand written code has a compelling reason to appear I<before>
the B<#DEBHELPER#> token. The B<#DEBHELPER#> token will generally contain
the code that start (F<postinst>) or stop (F<prerm>/F<preinst>) any
services the package is providing. Often (but not always), it is better
to let the code from B<#DEBHELPER#> run first. Common exceptions include
things like B<set -e>, initializing B<debconf> (when needed) and
special-cases like generation or hand-written management of configuration
files. These things should generally occur before the B<#DEBHELPER#>
token.

All debhelper commands that automatically generate code in this way let it
be disabled by the -n parameter (see above).

Note that the inserted code will be shell code, so you cannot directly use
it in a Perl script. If you would like to embed it into a Perl script, here
is one way to do that (note that I made sure that $1, $2, etc are set with
the set command):

  my $temp="set -e\nset -- @ARGV\n" . << 'EOF';
  #DEBHELPER#
  EOF
  if (system($temp)) {
     my $exit_code = ($? >> 8) & 0xff;
     my $signal = $? & 0x7f;
     if ($exit_code) {
         die("The debhelper script failed with error code: ${exit_code}");
     } else {
         die("The debhelper script was killed by signal: ${signal}");
     }
  }

=head2 Automatic generation of miscellaneous dependencies.

Some debhelper commands may make the generated package need to depend on
some other packages. For example, if you use L<dh_installdebconf(1)>, your
package will generally need to depend on debconf. Or if you use
L<dh_installxfonts(1)>, your package will generally need to depend on a
particular version of xutils. Keeping track of these miscellaneous
dependencies can be annoying since they are dependent on how debhelper does
things, so debhelper offers a way to automate it.

As of compat 14, debhelper will automatically inject the relevant
dependencies for you, since the dependency is done via a "relationship
substvar" (see L<https://lists.debian.org/debian-devel/2024/02/msg00230.html>
and L<https://lists.debian.org/debian-devel/2024/03/msg00030.html> for details).

In earlier compat levels, you have to manually specify the relevant substvars
in the relevant fields. Typically, B<${misc:Depends}> for the B<Depends>
field and B<${misc:Pre-Depends}> for the B<Pre-Depends> fields.

The variables listed here are entirely independent of the standard
B<${shlibs:Depends}> generated by L<dh_makeshlibs(1)>, and the
B<${perl:Depends}> generated by L<dh_perl(1)>. For compat 13 and earlier
you will also have to add these to the respective fields when relevant.

=head2 Package build directories

By default, all debhelper programs assume that the temporary directory used
for assembling the tree of files in a package is debian/I<package>.

Sometimes, you might want to use some other temporary directory. This is
supported by the B<-P> flag. For example, "B<dh_installdocs -Pdebian/tmp>", will
use B<debian/tmp> as the temporary directory. Note that if you use B<-P>, the 
debhelper programs can only be acting on a single package at a time. So if 
you have a package that builds many binary packages, you will need to also 
use the B<-p> flag to specify which binary package the debhelper program will
act on.

=head2 udebs

Debhelper includes support for udebs. To create a udeb with debhelper,
add "B<Package-Type: udeb>" to the package's stanza in F<debian/control>.
Debhelper will try to create udebs that comply with debian-installer
policy, by making the generated package files end in F<.udeb>, not
installing any documentation into a udeb, skipping over
F<preinst>, F<postrm>, F<prerm>, and F<config> scripts, etc.

=head1 ENVIRONMENT

This section describes some of the environment variables that influences
the behaviour of debhelper or which debhelper interacts with.

It is important to note that these must be actual environment variables in
order to affect the behaviour of debhelper (not simply F<Makefile> variables).
To specify them properly in F<debian/rules>, be sure to "B<export>" them. For
example, "B<export DH_VERBOSE>".

=over 4

=item B<DH_VERBOSE>

Set to a non-empty value to enable verbose mode.  Please see the B<-v> / B<--verbose>
option for details.

=item B<DH_QUIET>

Set to a non-empty value to enable quiet mode. Debhelper will not output commands calling
the upstream build system nor will dh print which subcommands are called
and depending on the upstream build system might make that more quiet, too.
This makes it easier to spot important messages but makes the output quite
useless as buildd log.

Ignored if DH_VERBOSE is also set or B<-v> / B<--verbose> is passed.

=item B<DH_COMPAT>

Temporarily specifies what compatibility level debhelper should run at,
overriding the default compat level of the source package.

=item B<DH_NO_ACT>

Set to B<1> to enable no-act mode.

=item B<DH_OPTIONS>

All debhelper tools will parse command line arguments listed in this variable
before any command option (as if they had been prepended to the command
line arguments).  Unfortunately, some third-party provided tools may not
support this variable and will ignore these command line arguments.

When using L<dh(1)>, it can be passed options that will be passed on to each
debhelper command, which is generally better than using DH_OPTIONS.

=item B<DH_ALWAYS_EXCLUDE>

If set, this adds the value the variable is set to to the B<-X> options of all
commands that support the B<-X> option. Moreover, B<dh_builddeb> will B<rm -rf>
anything that matches the value in your package build tree.

This can be useful if you are doing a build from a CVS source tree, in
which case setting B<DH_ALWAYS_EXCLUDE=CVS> will prevent any CVS directories
from sneaking into the package you build. Or, if a package has a source
tarball that (unwisely) includes CVS directories, you might want to export
B<DH_ALWAYS_EXCLUDE=CVS> in F<debian/rules>, to make it take effect wherever
your package is built.

Multiple things to exclude can be separated with colons, as in
B<DH_ALWAYS_EXCLUDE=CVS:.svn>

=item B<DH_EXTRA_ADDONS>

If set, this adds the specified dh addons to be run in the appropriate places
in the sequence of commands. This is equivalent to specifying the addon to run
with the --with flag in the debian/rules file. Any --without calls specifying
an addon in this environment variable will not be run.

This is intended to be used by downstreams or specific local configurations
that require a debhelper addon to be run during multiple builds without
having to patch a large number of rules file. If at all possible, this should
be avoided in favor of a --with flag in the rules file.

=item B<DH_COLORS>, B<DPKG_COLORS>

These variables can be used to control whether debhelper commands should use
colors in their textual output.  Can be set to "always", "auto" (the default),
or "never".

Note that B<DPKG_COLOR> also affects a number of dpkg related tools and
debhelper uses it on the assumption that you want the same color setting for
dpkg and debhelper.  In the off-hand chance you want different color setting
for debhelper, you can use B<DH_COLORS> instead or in addition to
B<DPKG_COLORS>.

=item B<NO_COLOR>

If no explicit request for color has been given (e.g. B<DH_COLORS> and
B<DPKG_COLORS> are both unset), the presence of this environment variable
cause the default color setting to be "never".

The variable is defined according to L<https://no-color.org/>.  In this
project, the environment variables (such as B<DH_COLORS>) are considered
an explicit request for color.

=item B<CFLAGS>, B<CPPFLAGS>, B<CXXFLAGS>, B<OBJCFLAGS>, B<OBJCXXFLAGS>, B<GCJFLAGS>, B<FFLAGS>, B<FCFLAGS>, B<LDFLAGS>

By default (in any non-deprecated compat level), debhelper will automatically
set these flags by using L<dpkg-buildflags(1)>, when they are unset.  If you
need to change the default flags, please use the features from
L<dpkg-buildflags(1)> to do this (e.g. B<DEB_BUILD_MAINT_OPTIONS=hardening=all>
or B<DEB_CPPFLAGS_MAINT_APPEND=-DCUSTOM_MACRO=true>) rather than setting the
concrete variable directly.

=item B<HOME>, B<XDG_*>

In compat 13 and later, these environment variables are reset before invoking
the upstream build system via the B<dh_auto_*> helpers.  The variables B<HOME>
(all B<dh_auto_*> helpers) and B<XDG_RUNTIME_DIR> (B<dh_auto_test> only) will
be set to a writable directory. All remaining variables and B<XDG_RUNTIME_DIR>
(except for during B<dh_auto_test>) will be cleared.

The B<HOME> directory will be created as an empty directory but it will be
reused between calls to B<dh_auto_*>.  Any content will persist until
explicitly deleted or B<dh_clean>.

=item B<DEB_BUILD_OPTIONS>

Please see L</Supported flags in DEB_BUILD_OPTIONS> for this environment
variable.

Please note that this variable should I<not> be altered by package maintainers
inside F<debian/rules> to change the behaviour of debhelper.  Instead, where
the package maintainer need these features, they should look disabling the
relevant feature directly (e.g. by overriding the concrete tools).

=item B<DEB_BUILD_MAINT_OPTIONS>

This is a dpkg specific environment variable (see e.g. L<dpkg-buildflags(1)>).
The debhelper tool suite silently ignores it.

It is documented here because it has a similar name to B<DEB_BUILD_OPTIONS>,
which make some people mistakenly assume that debhelper will also react to this
variable.

=back

=head2 Supported flags in DEB_BUILD_OPTIONS

The debhelper tool suite reacts to the following flags in B<DEB_BUILD_OPTIONS>.

=over 4

=item B<dherroron=obsolete-compat-levels>

I<This is a debhelper specific value.>

When B<dherroron> is present and set to B<obsolete-compat-levels>, then
debhelper tools will promote deprecation warnings for usage of old soon
to be removed compat levels into errors.

This is useful for automated checking for code relying on deprecated
compat levels that is scheduled for removal.

This option is intended for testing purposes; not production builds.

=item B<nostrip>

I<This value will change the content of the debs being built.  The .deb
packages built when this is set is therefore not bit-for-bit reproducible
with a regular build in the general case.>

This value will cause the official debhelper tools will skip actions and
helpers that either remove, detach or deduplicate debugging symbols in
ELF binaries.

This value affects L<dh_dwz(1)> and L<dh_strip(1)>.

=item B<nocheck>

This value will cause the official debhelper build systems to skip runs
of upstream test suites.

Package maintainers looking to avoid running the upstream tests should
B<not> rely on this.  Instead, they can add an empty override target
to skip B<dh_auto_test>.

This value affects L<dh_auto_test(1)>.

=item B<nodoc>

I<This value will change the content of the debs being built.  The .deb
packages built when this is set is therefore not bit-for-bit reproducible
with a regular build in the general case.>

This value will cause several debhelper tools to skip installation of
documentation such as manpages or upstream provided documentation.
Additionally, the tools will also ignore if declared documentation is
"missing" on the assumption that the documentation has not been built.

This value effects tools I<like> L<dh_installdocs(1)>, which I<knows>
it is working with documentation.

=item B<notrimdch>

I<This value will change the content of the debs being built.  The .deb
packages built when this is set is therefore not bit-for-bit reproducible
with a regular build in the general case.>

This value will cause L<dh_installchangelogs(1)> to act as if it
had been passed the B<--no-trim> option, forcing it to forgo removing
older entries from changelogs.

=item B<noautodbgsym>, B<noddebs>

I<The official name is noautodbgsym.  The noddebs variant is accepted
for historical reasons.>

This value causes debhelper to skip the generation of automatically
generated debug symbol packages.

This value affects L<dh_strip(1)>.

=item B<parallel=N>

This value enables debhelper to use up to B<N> threads or processes
(subject to parameters like B<--no-parallel> and B<--max-parallel=M>).
Not all debhelper tools work with parallel tasks and may silently
ignore the request.

This value affects many debhelper tools.  Most notably B<dh_auto_*>,
which will attempt to run the underlying upstream build system with
that number of threads.

=item B<terse>

This value will cause the official debhelper build systems to configure
upstream builds to be terse (i.e. reduce verbosity in their output).
This is subject to the upstream and the debhelper build system
supporting such features.

This value affects most B<dh_auto_*> tools directly. For commands
provided by the debhelper package, it also causes the tools to act like
the B<DH_QUIET> environment variable was non-empty.

=back

Unknown flags are silently ignored.

Note third-party debhelper-like tools or third-party provided build systems
may or may not react to the above flags.  This tends to depend on
implementation details of the tool.

=head1 SEE ALSO

=over 4

=item L<debhelper-compat-upgrade-checklist(7)>

List of supported compat levels and an upgrade checklist for each of them.

=item F</usr/share/doc/debhelper/examples/>

A set of example F<debian/rules> files that use debhelper.

=item L<http://joeyh.name/code/debhelper/>

Debhelper web site.

=back

=head1 AUTHOR

Joey Hess <joeyh@debian.org>

=cut
