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* Getting Started
In order to use /justbuild/, first make sure that ~just~ and ~just-mr~ are
available in your ~PATH~.
** Creating a new project
/justbuild/ needs to know the root of the project worked on. By default, it
searches upwards from the current directory till it finds a marker. Currently,
we support three different markers: the files ~ROOT~ and ~WORKSPACE~ or the
directory ~.git~. Lets create a new project by creating one of those markers:
#+BEGIN_SRC sh
$ touch ROOT
#+END_SRC
** Creating a generic target
By default, targets are described in ~TARGETS~ files. These files contain a
~JSON~ object with the target name as key and the target description as value. A
target description is an object with at least a single mandatory field:
~"type"~. This field specifies which rule (built-in or user-defined) to apply
for this target.
A simple target that only executes commands can be created using the built-in
~"generic"~ rule, which requires at least one command and one output file or
directory. To create such a target, create the file ~TARGETS~ with the following
content:
#+SRCNAME: TARGETS
#+BEGIN_SRC js
{ "greeter":
{ "type": "generic"
, "cmds": ["echo -n 'Hello ' > out.txt", "cat name.txt >> out.txt"]
, "outs": ["out.txt"]
, "deps": ["name.txt"]
}
}
#+END_SRC
In this example, the ~"greeter"~ target will run two commands to produce the
output file ~out.txt~. The second command depends on the input file ~name.txt~
that we need to create as well:
#+BEGIN_SRC sh
$ echo World > name.txt
#+END_SRC
** Building a generic target
To build a target, we need to run ~just~ with the subcommand ~build~:
#+BEGIN_SRC sh
$ just build greeter
INFO: Requested target is [["@","","","greeter"],{}]
INFO: Analysed target [["@","","","greeter"],{}]
INFO: Export targets found: 0 cached, 0 uncached, 0 not eligible for caching
INFO: Discovered 1 actions, 0 trees, 0 blobs
INFO: Building [["@","","","greeter"],{}].
INFO: Processed 1 actions, 0 cache hits.
INFO: Artifacts built, logical paths are:
out.txt [557db03de997c86a4a028e1ebd3a1ceb225be238:12:f]
$
#+END_SRC
The subcommand ~build~ just builds the artifact but does not stage it to any
user-defined location on the file system. Instead it reports a description
of the artifact consisting of ~git~ blob identifier, size, and type (in
this case ~f~ for non-executable file). To also stage the produced artifact to
the working directory, use the ~install~ subcommand and specify the output
directory:
#+BEGIN_SRC sh
$ just install greeter -o .
INFO: Requested target is [["@","","","greeter"],{}]
INFO: Analysed target [["@","","","greeter"],{}]
INFO: Export targets found: 0 cached, 0 uncached, 0 not eligible for caching
INFO: Discovered 1 actions, 0 trees, 0 blobs
INFO: Building [["@","","","greeter"],{}].
INFO: Processed 1 actions, 1 cache hits.
INFO: Artifacts can be found in:
/tmp/tutorial/out.txt [557db03de997c86a4a028e1ebd3a1ceb225be238:12:f]
$ cat out.txt
Hello World
$
#+END_SRC
Note that the ~install~ subcommand initiates the build a second time, without
executing any actions as all actions are being served from cache. The produced
artifact is identical, which is indicated by the same hash/size/type.
Alternatively, we could also directly request the artifact ~out.txt~ from
/justbuild/'s CAS (content-addressable storage) and print it on the command line
via:
#+BEGIN_SRC sh
$ just install-cas [557db03de997c86a4a028e1ebd3a1ceb225be238:12:f]
Hello World
$
#+END_SRC
The canonical way of requesting an object from the CAS is, as just shown, to
specify the full triple of hash, size, and type, separated by colons and
enclosed in square brackets. To simplify usage, the brackets can be omitted
and the size and type fields have the default values ~0~ and ~f~, respectively.
While the default value for the size is wrong for all but one string, the hash
still determines the content of the file and hence the local CAS is still
able to retrieve the file. So the typical invocation would simply specify the
hash.
#+BEGIN_SRC sh
$ just install-cas 557db03de997c86a4a028e1ebd3a1ceb225be238
Hello World
$
#+END_SRC
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