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Docs: Add section for script parsing

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Document `!` and `:`.
Add warning that semicolons need spaces.
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Krystine Sherwin 2024-06-11 13:17:56 +12:00
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docs/source/getting_started/scripting_intro.rst
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@ -8,10 +8,40 @@ file format and how you can make your own synthesis scripts.
Yosys script files typically use the :file:`.ys` extension and contain a set of
commands for Yosys to run sequentially. These commands are the same ones we
were using on the previous page like :cmd:ref:`read_verilog` and
:cmd:ref:`hierarchy`. As with the interactive shell, each command consists of
the command name, and an optional whitespace separated list of arguments.
Commands are terminated with the newline character, or by a semicolon (;). Empty
lines, and lines starting with the hash sign (#), are ignored.
:cmd:ref:`hierarchy`.
Script parsing
~~~~~~~~~~~~~~
As with the interactive shell, each command consists of the command name, and an
optional whitespace separated list of arguments. Commands are terminated with
the newline character, and anything after a hash sign ``#`` is a comment (i.e.
it is ignored).
It is also possible to terminate commands with a semicolon ``;``. This is
particularly useful in conjunction with the ``-p <command>`` command line
option, where ``<command>`` can be a string with multiple commands separated by
semicolon. In-line comments can also be made with the colon ``:``, where the end
of the comment is a semicolon ``;`` or a new line.
.. code-block::
:caption: Using the ``-p`` option
$ yosys -p "read_verilog fifo.v; :this is a comment; prep"
.. warning::
The space after the semicolon is required for correct parsing. ``log a;log
b;`` for example will display ``a;log b`` instead of ``a`` and ``b`` as might
be expected.
Another special character that can be used in Yosys scripts is the bang ``!``.
Anything after the bang will be executed as a shell command. This can only be
terminated with a new line. Any semicolons, hashes, or other special characters
will be passed to the shell. If an error code is returned from the shell it
will be raised by Yosys. :cmd:ref:`exec` provides a much more flexible way of
executing commands, allowing the output to be logged and more control over when
to generate errors.
The synthesis starter script
~~~~~~~~~~~~~~~~~~~~~~~~~~~~