dev-manual: Updates to the "Understanding Recipe Syntax" section.
Paul Eggleton sent me some feedback on this section. I implemented his suggestions. Changes were minor. One included a cross-link to the BitBake User Manual. (From yocto-docs rev: e9b5f252a1368b8c231dd659428a18eacf9757af) Signed-off-by: Scott Rifenbark <scott.m.rifenbark@intel.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
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<title>Understanding Recipe Syntax</title>
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<para>
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The basic items that make up a BitBake recipe file are
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as follows:
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Understanding recipe file syntax is important for
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writing recipes.
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The following list overviews the basic items that make up a
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BitBake recipe file.
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For more complete BitBake syntax descriptions, see the
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"<ulink url='&YOCTO_DOCS_BB_URL;#bitbake-user-manual-metadata'>Syntax and Operators</ulink>"
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chapter of the BitBake User Manual.
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<itemizedlist>
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<listitem><para><emphasis>Variable Assignments and Manipulations:</emphasis>
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Variable assignments allow a value to be assigned to a
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<filename>local.conf</filename> file for variables
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that are allowed to come through from the external
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environment.
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Doing so allows you to actually set variables from
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the external environment that would otherwise be
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overwritten.</para>
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<para>Here is an example:
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</para>
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<para>Here is an example where
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<filename>VAR1</filename> is set to "New value" if
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it is currently empty.
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However, if <filename>VAR1</filename> has already been
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set, it remains unchanged:
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<literallayout class='monospaced'>
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VAR1 ?= "New value"
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</literallayout>
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In the previous example, <filename>VAR1</filename> is
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set to "New value" if it is currently empty.
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However, if <filename>VAR1</filename> has already been
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set, it remains unchanged.</para>
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<para>In this next example, <filename>VAR1</filename>
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In this next example, <filename>VAR1</filename>
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is left with the value "Original value":
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<literallayout class='monospaced'>
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VAR1 = "Original value"
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@ -1632,7 +1635,7 @@
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</literallayout>
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</para></listitem>
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<listitem><para><emphasis>Shell Function Syntax:</emphasis>
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Use shell function syntax as if you were writing a shell
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Write shell functions as if you were writing a shell
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script when you describe a list of actions to take.
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You should ensure that your script works with a generic
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<filename>sh</filename> and that it does not require
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