Yaml Assistant Reference

When developing assistants, please make sure that you read proper version of documentation. The Yaml DSL of devassistant is still evolving rapidly, so consider yourself warned.

This is a reference manual to writing yaml assistants. Yaml assistants use a special DSL defined on this page. For real examples, have a look at assistants in our Github repo.

Why the hell another DSL?
When we started creating DevAssistant and we were asking people who work in various languages whether they’d consider contributing assistants for those languages, we hit the “I’m not touching Python” barrier. Since we wanted to keep the assistants consistent (centralized logging, sharing common functionality, same backtraces, etc...), we created a new DSL. So now we have something that everyone complains about, including Pythonists, which seems to be consistent too ;)

Assistant Roles

There are three types of assistants:

creator assistants are meant to create new projects from scratch, they’re accessed using da binary
modifier assistants are used for modifying existing projects previously created by DevAssistant
preparer assistants are used for setting up environment for already existing projects (located e.g. at remote SCM etc.) that may or may not have been creating by DevAssistant

The role is implied by assistant location in one of the load path directories, as mentioned in Assistants Loading Mechanism.

All the rules mentioned in this document apply to all types of assistants, with exception of sections Modifier Assistants and Preparer Assistants that talk about specifics of Modifier, resp. Preparer assistants.

Assistant Name

Assistant name is a short name used on command line, e.g. python. It should also be the only top-level yaml mapping in the file (that means just one assistant per file). Each assistant should be placed in a file that’s named the same as the assistant itself (e.g. python assistant in python.yaml file).

Assistant Content

The top level mapping has to be mapping from assistant name to assistant attributes, for example:

  fullname: Python
  # etc.

List of allowed attributes follows (all of them are optional, and have some sort of reasonable default, it’s up to your consideration which of them to use):

a verbose name that will be displayed to user (Python Assistant)
a (verbose) description to show to user (Bla bla create project bla bla)
dependencies (and dependencies_*)
specification of dependencies, see below Dependencies
specification of arguments, see below Args
specification of used files, see below Files
run (and run_*)
specification of actual operations, see below Run
directory where to take files (templates, helper scripts, ...) from. Defaults to base directory from where this assistant is taken + files. E.g. if this assistant is ~/.devassistant/assistants/crt/path/and/more.yaml, files will be taken from ~/.devassistant/files/crt/path/and/more by default.
absolute or relative path to icon of this assistant (will be used by GUI). If not present, a default path will be used - this is derived from absolute assistant path by replacing assistants by icons and .yaml by .svg - e.g. for ~/.devassistant/assistants/crt/foo/bar.yaml, the default icon path is ~/.devassistant/icons/crt/foo/bar.svg


Yaml assistants can express their dependencies in multiple sections.

  • Packages from section dependencies are always installed.

  • If there is a section named dependencies_foo, then dependencies from this section are installed iff foo argument is used (either via commandline or via gui). For example:

    $ da python --foo
  • These rules differ for Modifier Assistants

Each section contains a list of mappings dependency type: [list, of, deps]. If you provide more mappings like this:

- rpm: [foo]
- rpm: ["@bar"]

they will be traversed and installed one by one. Supported dependency types:

the dependency list can contain RPM packages or YUM groups (groups must begin with @ and be quoted, e.g. "@Group name")

installs dependencies from snippet or other dependency section of this assistant. For example:

- call: foo # will install dependencies from snippet "foo", section "dependencies"
- call: foo.dependencies_bar # will install dependencies from snippet "foo", section "bar"
- call: self.dependencies_baz # will install dependencies from section "dependencies_baz" of this assistant
if, else

conditional dependency installation. For more info on conditions, Run below. A very simple example:

- if $foo:
  - rpm: [bar]
- else:
  - rpm: [spam]

Full example:

dependencies: - rpm: [foo, "@bar"]

- rpm: [beans, eggs]
- if $with_spam:
  - call: spam.spamspam
- rpm: [ham]


Arguments are used for specifying commandline arguments or gui inputs. Every assistant can have zero to multiple arguments.

The args section of each yaml assistant is a mapping of arguments to their attributes:

    - -n
    - --name
  help: Name of the project to create.

Available argument attributes:

specifies commandline flags to use for this argument. The longer flag (without the --, e.g. name from --name) will hold the specified commandline/gui value during run section, e.g. will be accessible as $name.
a help string
one of {true,false} - is this argument required?
how many parameters this argument accepts, one of {?,*,+} (e.g. {0 or 1, 0 or more, 1 or more})
a default value (this will cause the default value to be set even if the parameter wasn’t used by user)
one of {store_true, [default_iff_used, value]} - the store_true value will create a switch from the argument, so it won’t accept any parameters; the [default_iff_used, value] will cause the argument to be set to default value value iff it was used without parameters (if it wasn’t used, it won’t be defined at all)
name of the snippet to load this argument from; any other specified attributes will override those from the snippet By convention, some arguments should be common to all or most of the assistants. See Common Assistant Behaviour

Gui Hints

GUI needs to work with arguments dynamically, choose proper widgets and offer sensible default values to user. These are not always automatically retrieveable from arguments that suffice for commandline. For example, GUI cannot meaningfully prefill argument that says it “defaults to current working directory”. Also, it cannot tell whether to choose a widget for path (with the “Browse ...” button) or just a plain text field.

Because of that, each argument can have gui_hints attribute. This can specify that this argument is of certain type (path/str/bool) and has a certain default. If not specified in gui_hints, the default is taken from the argument itself, if not even there, a sensible “empty” default value is used (home directory/empty string/false). For example:

    - [-p, --path]
      type: path
      default: $(pwd)/foo

If you want your assistant to work properly with GUI, it is good to use gui_hints (currently, it only makes sense to use it for path attributes, as str and bool get proper widgets and default values automatically).


This section serves as a list of aliases of files stored in one of the files dirs of DevAssistant. E.g. if your assistant is assistants/crt/foo/bar.yaml, then files are taken relative to files/crt/foo/bar/ directory. So if you have a file files/crt/foo/bar/spam, you can use:

  spam: &spam
    source: spam

This will allow you to reference the spam file in run section as *spam without having to know where exactly it is located in your installation of DevAssistant.


Run sections are the essence of DevAssistant. They are responsible for preforming all the tasks and actions to set up the environment and the project itself. By default, section named run is invoked (this is a bit different for Modifier Assistants). If there is a section named run_foo and foo argument is used, then only run_foo is invoked. This is different from dependencies sections, as the default dependencies section is used every time.

Every run section is a sequence of various commands, mostly invocations of commandline. Each command is a mapping command_type: command. During the execution, you may use logging (messages will be printed to terminal or gui) with following levels: DEBUG, INFO, WARNING, ERROR, CRITICAL. By default, messages of level INFO and higher are logged. As you can see below, there is a separate log_* command type for logging, but some other command types can also log various messages. Log messages with levels ERROR and CRITICAL terminate execution of DevAssistant imediatelly.

Run sections allow you to use variables with certain rules and limitations. See below.

List of supported commands follows:

runs given command on commandline, aborts execution of the invoked assistant if it fails. Note: cd is a special cased command, which doesn’t do shell expansion other than user home dir (~) expansion.
the i option makes the command execution be logged at INFO level (default is DEBUG), therefore visible to user
logs given message at level specified by the last letter in log_X. If the level is e or c, the execution of the assistant is interrupted immediately.
  • c creates .devassistant file (containing some sane initial meta information about the project) in given directory
  • dda_dependencies let’s you install dependencies from .devassistant file (DevAssistant will use dependencies from original assistant and specified dependencies attribute, if any - this has the same structure as dependencies in normal assistants, and is evaluated in current assistant context, not the original assistant context)
  • dda_run will execute a series of commands from run section from .devassistant (in context of current assistant)
if <expression>, else
conditional execution. The condition must be an Expression.
for <var> in <expression>
(for example for $i in $(ls)) - loop over result of given expression (if it is string, which almost always is, it is split on whitespaces)
assigns result of an Expression to the given variable (doesn’t interrupt the assistant execution if command fails)
$success, $foo
assigns logical result (True/False) of evaluating an Expression to $success and result to $foo (same as above)
run another section of this assistant (e.g.``call: self.run_foo``) of a snippet run section (call: snippet_name.run_foo) at this place and then continue execution

run a whole section in SCL environment of one or more SCLs (note: you must use the scriptlet name - usually enable - because it might vary) - for example:

- scl enable python33 postgresql92:
  - cl_i: python --version
  - cl_i: pgsql --version


Initially, variables are populated with values of arguments from commandline/gui and there are no other variables defined for creator assistants. For modifier assistants global variables are prepopulated with some values read from .devassistant. You can either define (and assign to) your own variables or change the values of current ones.

The variable scope works as follows:

  • When invoking run section (from the current assistant or snippet), the variables get passed by value (e.g. they don’t get modified for the remainder of this scope).
  • As you would probably expect, variables that get modified in if and else sections are modified until the end of the current scope.

All variables are global in the sense that if you call a snippet or another section, it can see all the arguments that are defined.


Expressions are expressions, really. They are used in assignments, conditions and as loop “iterables”. Every expression has a logical result (meaning success - True or failure - False) and result (meaning output). Logical result is used in conditions and variable assignments, result is used in variable assignments and loops. Note: when assigned to a variable, the logical result of an expression can be used in conditions as expected; the result is either True/False.

Syntax and semantics:

  • $foo
    • if $foo is defined:
      • logical result: True iff value is not empty and it is not False
      • result: value of $foo
    • otherwise:
      • logical result: False
      • result: empty string
  • $(commandline command) (yes, that is a command invocation that looks like running command in a subshell)
    • if commandline command has return value 0:
      • logical result: True
    • otherwise:
      • logical result: False
    • regardless of logical result, result always contains both stdout and stderr lines in the order they were printed by commandline command
  • not - negates the logical result of an expression, while leaving result intact, can only be used once (no, you can’t use not not not $foo, sorry)
  • defined $foo - works exactly as $foo, but has logical result True even if the value is empty or False


When using variables that contain user input, they should always be quoted in the places where they are used for bash execution. That includes cl* commands, conditions that use bash return values and variable assignment that uses bash.

Modifier Assistants

Modifier assistants are assistants that are supposed to work with already created project. They must be placed under mod subdirectory of one of the load paths, as mentioned in Assistants Loading Mechanism.

There are few special things about modifier assistants:

  • They read the whole .devassistant file and make its contents available as any other variables (notably $subassistant_path).
  • They use dependency sections according to the normal rules + they use all the sections that are named according to loaded $subassistant_path, e.g. if $subassistant_path is [foo, bar], dependency sections dependencies, dependencies_foo and dependencies_foo_bar will be used as well as any sections that would get installed according to specified parameters. The rationale behind this is, that if you have e.g. eclipse modifier that should work for both python django and python flask projects, chance is that they have some common dependencies, e.g. eclipse-pydev. So you can just place these common dependencies in dependencies_python and you’re done (you can possibly place special per-framework dependencies into e.g. dependencies_python_django).
  • By default, they don’t use run section. Assuming that $subassistant_path is [foo, bar], they first try to find run_foo_bar, then run_foo and then just run. The first found is used. If you however use cli/gui parameter spam and section run_spam is present, then this is run instead.

Preparer Assistants

Preparer assistants are assistants that are supposed to set up environment for executing arbitrary tasks or prepare environment and checkout existing upstream projects (possibly using their .devassistant file, if they have it). Preparers must be placed under prep subdirectory of one of the load paths, as mentioned in Assistants Loading Mechanism.

Preparer assistants commonly utilize the dda_dependencies and dda_run commands in run section.

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