Provided by: debhelper_13.6ubuntu1_all 
NAME
dh_assistant - tool for supporting debhelper tools and provide introspection
SYNOPSIS
dh_assistant command [additional options]
DESCRIPTION
dh_assistant is a debhelper program that provides introspection into the debhelper stack to assist third-
party tools (e.g. linters) or third-party debhelper implementations not using the debhelper script API
(e.g., because they are not written in Perl).
COMMANDS
The dh_assistant supports the following commands:
active-compat-level (JSON)
Synopsis: dh_assistant active-compat-levels
Outputs information about which compat level the package is using.
For packages without valid debhelper compatibility information (whether missing, ambiguous, not supported
or simply invalid), this command operates on a "best effort" basis and may abort when error instead of
providing data.
The returned JSON dictionary contains the following key-value pairs:
active-compat-level
The compat level that debhelper will be using. This is the same as DH_COMPAT when present or else
declared-compat-level. This can be null when no compat level can be detected.
declared-compat-level
The compat level that the package declared as its default compat level. This can be null if the
package does not declare any compat level at all.
declared-compat-level-source
Defines how the compat level was declared. This is null (for the same reason as declared-compat-
level) or one of:
debian/compat
The compatibility level was declared in the first line debian/compat file.
Build-Depends: debhelper-compat (= <C>)
The compatibility was declared in the debian/control via a build dependency on the debhelper-
compat (= <C>) package in the Build-Depends field. In the output, the C is replaced by the
actual compatibility level. A full example value would be:
Build-Depends: debhelper-compat (= 13)
supported-compat-levels (JSON, CRFA)
Synopsis: dh_assistant supported-compat-levels
Outputs information about which compat levels, this build of debhelper knows about.
This command accepts no options or arguments.
which-build-system (JSON)
Synopsis: dh_assistant which-build-system [build step] [build system options]
Output information about which build system would be used for a particular build step. The build step
must be one of configure, build, test, install or clean and must be the first argument after which-build-
system when provided. If omitted, it defaults to configure as it is the most reliable step to use auto-
detection on in a clean source directory. Note that build steps do not always agree when using auto-
detection - particularly if the configure step has not been run.
Additionally, the clean step can also provide "surprising" results for builds that rely on a separate
build directory. In such cases, debhelper will return the first build system that uses a separate build
directory rather than the one build system that configure would detect. This is generally a cosmetic
issue as both build systems are all basically a glorified rm -fr builddir and more precise detection is
functionally irrelevant as far as debhelper is concerned.
The option accepts all debhelper build system arguments - i.e., options you can pass to all of the
dh_auto_* commands plus (for the install step) the --destdir option. These options affect the output and
auto-detection in various ways. Passing -S or --buildsystem overrides the auto-detection (as it does for
dh_auto_*) but it still provides introspection into the chosen build system.
Things that are useful to know about the output:
• The key build-system is the build system that would be used by debhelper for the given step (with the
given options, debhelper compat level, environment variables and the given working directory). When
-S and --buildsystem are omitted, this is the result of debhelper's auto-detection logic.
The value is valid as a parameter for the --buildsystem option.
The special value none is used to denote that no build system would be used. This value is not
present in --list parameter for the dh_auto_* commands, but since debhelper/12.9 the value is
accepted for the --buildsystem option.
Note that auto-detection is subject to limitations in regards to third-party build systems. While
debhelper does support auto-detecting some third-party build systems, they must be installed for the
detection to work. If they are not installed, the detection logic silently skips that build system
(often resulting in build-system being none in the output).
• The build-directory and buildpath values serve different but related purposes. The build-directory
generally mirrors the --builddirectory option where as buildpath is the output directory that
debhelper will use. Therefore the former will often be null when --builddirectory has not been
passed while the latter will generally not be null (except when build-system is none).
• The dest-directory (--destdir) is undefined for all build steps except the install build step (will
be output as null or absent). For the same reason, --destdir should only be passed for install build
step.
Note that if not specified, this value is currently null by default.
• The parallel value is subject to DEB_BUILD_OPTIONS. Notably, if that does not include the parallel
keyword, then parallel field in the output will always be 1.
• Most fields in the output can be null. Particular if there is no build system is detected (or when
--buildsystem=none). Additionally, many of the fields can be null even if there is a build system if
the build system does not use/set/define that variable.
COMMAND TAGS
Most commands have one or more of the following "tags" associated with them. Their meaning is defined
here.
JSON
The command provides JSON output. See "JSON OUTPUT" for details.
CRFA
Mnemonic "Can be Run From Anywhere"
Most commands must be run inside a source package root directory (a directory containing
debian/control) because debhelper will need the package metadata to lookup the information. Any
command with this tag are exempt from this requirement and is expected to work regardless of where
they are run.
JSON OUTPUT
Most commands uses JSON format as output. Consumers need to be aware that:
• Additional keys may be added at any time. For backwards compatibility, the absence of a key should
in general be interpreted as null unless another default is documented or would be "obvious" for that
case.
• Many keys can be null/undefined in special cases. As an example, some information may be unavailable
when this command is run directly from the debhelper source (git repository).
The output will be prettified when stdout is detected as a terminal. If you need to pipe the output to a
pager/file (etc.) and still want it prettified, please use an external JSON formatter. An example of
this:
dh_assistant supported-compat-levels | python3 -m json.tool | less
SEE ALSO
debhelper(7)
This program is a part of debhelper.
13.6ubuntu1 2022-02-07 DH_ASSISTANT(1)