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dev-manual: Edits to the "Understanding Recipe Syntax" section. 

Added a new "Overrides" bullet item and fixed some minor issues
pointed out by Paul Eggleton.

(From yocto-docs rev: 44ff3d82985fa304c5641570fe72cf6a8ddabaa3)

Signed-off-by: Scott Rifenbark <scott.m.rifenbark@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
This commit is contained in:
Scott Rifenbark 2014-06-02 17:54:51 +03:00 committed by Richard Purdie
parent d57b5e5149
commit 95a5fadc15
1 changed files with 28 additions and 4 deletions
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32
documentation/dev-manual/dev-manual-common-tasks.xml
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@ -1498,7 +1498,7 @@
or tabs after the slash character.
</note>
</para></listitem>
<listitem><para><emphasis>Using Variables: <filename>{...}</filename></emphasis> -
<listitem><para><emphasis>Using Variables: <filename>${...}</filename></emphasis> -
Use the <filename>${&lt;varname&gt;}</filename> syntax to
access the contents of a variable:
<literallayout class='monospaced'>
@ -1615,6 +1615,30 @@
CFLAGS_prepend_sh4 = " file://fix-makefile.patch"
</literallayout>
</para></listitem>
<listitem><para><emphasis>Overrides:</emphasis> -
You can use overrides to set a value conditionally,
typically on how the recipe is being built.
For example, to set the
<ulink url='&YOCTO_DOCS_REF_URL;#var-KBRANCH'><filename>KBRANCH</filename></ulink>
variable's value to "standard/base" for any target
<ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE'><filename>MACHINE</filename></ulink>,
except for qemuarm where it should be set to
"standard/arm-versatile-926ejs", you would do the
following:
<literallayout class='monospaced'>
KBRANCH = "standard/base"
KBRANCH_qemuarm = "standard/arm-versatile-926ejs"
</literallayout>
Overrides are also used to separate alternate values
of a variable in other situations.
For example, when setting variables such as
<ulink url='&YOCTO_DOCS_REF_URL;#var-FILES'><filename>FILES</filename></ulink>
and
<ulink url='&YOCTO_DOCS_REF_URL;#var-RDEPENDS'><filename>RDEPENDS</filename></ulink>,
that are specific to individual packages produced by
a recipe, you should always use an override that
specifies the name of the package.
</para></listitem>
<listitem><para><emphasis>Indentation:</emphasis>
Use spaces for indentation rather than than tabs.
For shell functions, both currently work.
@ -1623,13 +1647,13 @@
Realize that some layers have a policy to use spaces
for all indentation.
</para></listitem>
<listitem><para><emphasis>Using Python for Complex Operations: <filename>${@&lt;variable&gt;}</filename></emphasis> -
<listitem><para><emphasis>Using Python for Complex Operations: <filename>${@&lt;python_code&gt;}</filename></emphasis> -
For more advanced processing, it is possible to use
Python code during variable assignments (e.g.
search and replacement on a variable).</para>
<para>You indicate Python code using the
<filename>${@&lt;variable&gt;}</filename> syntax for the
variable assignment:
<filename>${@&lt;python_code&gt;}</filename>
syntax for the variable assignment:
<literallayout class='monospaced'>
SRC_URI = "ftp://ftp.info-zip.org/pub/infozip/src/zip${@d.getVar('PV',1).replace('.', '')}.tgz
</literallayout>