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

(From yocto-docs rev: 97e5025ccff55efd077fdaf9b2d65eae5b59bc2b)

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 2014-05-07 23:50:59 +03:00 committed by Richard Purdie
parent 1744a1e5b9
commit ab864d71fb
1 changed files with 49 additions and 71 deletions
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120
documentation/dev-manual/dev-manual-common-tasks.xml
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@ -1290,6 +1290,21 @@
The basic items that make up a BitBake recipe file are
as follows:
<itemizedlist>
<listitem><para><emphasis>Variable Assignments and Manipulations:</emphasis>
Variable assignments allow a value to be assigned to a
variable.
The assignment can be static text or might include
the contents of other variables.
In addition to the assignment, appending and prepending
operations are also supported.</para>
<para>The following example shows some of the ways
you can use variables in recipes:
<literallayout class='monospaced'>
S = "${WORKDIR}/postfix-${PV}"
CFLAGS += "-DNO_ASM"
SRC_URI_append = " file://fixup.patch"
</literallayout>
</para></listitem>
<listitem><para><emphasis>Functions:</emphasis>
Functions provide a series of actions to be performed.
You usually use functions to override the default
@ -1313,25 +1328,9 @@
new functions are not replacing or complimenting the
default functions.
You can implement functions in Python
instead of <filename>sh</filename>.
instead of shell.
Both of these options are not seen in the majority of
recipes.</para></listitem>
<listitem><para><emphasis>Variable Assignments and Manipulations:</emphasis>
Variable assignments allow a value to be assigned to a
variable.
The assignment can be static text or might include
the contents of other variables.
In addition to the assignment, appending and prepending
operations are also supported.</para>
<para>The following example shows some of the ways
you can use variables in recipes:
<literallayout class='monospaced'>
S = "${WORKDIR}/postfix-${PV}"
PR = "r4"
CFLAGS += "-DNO_ASM"
SRC_URI_append = "file://fixup.patch"
</literallayout>
</para></listitem>
<listitem><para><emphasis>Keywords:</emphasis>
BitBake recipes use only a few keywords.
You use keywords to include common
@ -1389,7 +1388,8 @@
</literallayout>
</para></listitem>
<listitem><para><emphasis>Quote All Assignments: <filename>"&lt;value&gt;"</filename></emphasis> -
Use double quotes to make all variable assignments.
Use double quotes around the value in all variable
assignments.
<literallayout class='monospaced'>
VAR1 = "${OTHERVAR}"
VAR2 = "The version is ${PV}"
@ -1401,13 +1401,14 @@
unset.
Use the question mark followed by the equal sign
(<filename>?=</filename>) to make a "soft" assignment
used for conditional assignment.</para>
<para>Typically, you use conditional assignment to
provide
a default value for use when no specific definition is
provided by the machine or distro configuration in
your <filename>local.conf</filename> configuration.
</para>
used for conditional assignment.
Typically, "soft" assignments are used in the
<filename>local.conf</filename> file for variables
that are allowed to come through from the external
environment.
Doing so allows you to actually set variables from
the external environment that would otherwise be
overwritten.</para>
<para>Here is an example:
<literallayout class='monospaced'>
VAR1 ?= "New value"
@ -1455,7 +1456,9 @@
This operator does not add any additional space.
Also, the operator is applied after all the
<filename>+=</filename>, and
<filename>=+</filename> operators have been applied.
<filename>=+</filename> operators have been applied and
after all <filename>=</filename> assignments have
occurred.
</para>
<para>The following example shows the space being
explicitly added to the start to ensure the appended
@ -1470,26 +1473,17 @@
<literallayout class='monospaced'>
SRC_URI_append_sh4 = " file://fix-makefile.patch"
</literallayout>
<note>
The appended information is a variable itself.
Therefore, it is possible to use the
<filename>+=</filename> or
<filename>=+</filename> operators to assign
variables to the <filename>_append</filename>
information:
<literallayout class='monospaced'>
SRC_URI_append = " file://fix-makefile.patch"
SRC_URI_append += "file://fix-install.patch"
</literallayout>
</note>
</para></listitem>
<listitem><para><emphasis>Prepending: <filename>_prepend</filename></emphasis> -
Use the <filename>_prepend</filename> operator to
prepend values to existing variables.
This operator does not add any additional space.
Also, it is applied after all the
<filename>+=</filename> and
<filename>=+</filename> operators have been applied.
This operator does not add any additional space.
Also, the operator is applied after all the
<filename>+=</filename>, and
<filename>=+</filename> operators have been applied and
after all <filename>=</filename> assignments have
occurred.
</para>
<para>The following example shows the space being
explicitly added to the end to ensure the prepended
@ -1504,45 +1498,29 @@
<literallayout class='monospaced'>
CFLAGS_prepend_sh4 = " file://fix-makefile.patch"
</literallayout>
<note>
The appended information is a variable itself.
Therefore, it is possible to use the
<filename>+=</filename> or
<filename>=+</filename> operators to assign
variables to the <filename>_prepend</filename>
information:
<literallayout class='monospaced'>
CFLAGS_prepend = "-I${S}/myincludes "
CFLAGS_prepend += "-I${S}/myincludes2 "
</literallayout>
Notice in this example no spacing is used at the
front of the value string.
Recall that the <filename>+=</filename> operator
adds space itself.
</note>
</para></listitem>
<listitem><para><emphasis>Spaces as Compared to Tabs:</emphasis>
<listitem><para><emphasis>Indentation:</emphasis>
Use spaces for indentation rather than than tabs.
Both currently work, however it is a policy decision
of the Yocto Project to use tabs in shell functions
and spaces in Python.
However, realize that some layers use a policy of all
spaces.
For shell functions, both currently work.
However, it is a policy decision of the Yocto Project
to use tabs in shell functions.
Realize that some layers have a policy to use spaces
for all indentation.
</para></listitem>
<listitem><para><emphasis>Using Python for Complex Operations: <filename>${@...}</filename></emphasis> -
<listitem><para><emphasis>Using Python for Complex Operations: <filename>${@&lt;variable&gt;}</filename></emphasis> -
For more advanced processing, it is possible to use
Python code during variable assignments (e.g.
search and replacement on a variable).</para>
<para>You indicate Python code using a preceding
<filename>@</filename> character in the variable
assignment:
<para>You indicate Python code using the
<filename>${@&lt;variable&gt;}</filename> syntax for the
variable assignment:
<literallayout class='monospaced'>
CXXFLAGS := "${@'${CXXFLAGS}'.replace('-frename-registers', '')}"
SRC_URI = "ftp://ftp.info-zip.org/pub/infozip/src/zip${@d.getVar('PV',1).replace('.', '')}.tgz
</literallayout>
</para></listitem>
<listitem><para><emphasis>Shell Syntax:</emphasis>
Use shell syntax as if you were writing a shell script
when you describe a list of actions to take.
<listitem><para><emphasis>Shell Function Syntax:</emphasis>
Use shell function syntax as if you were writing a shell
script when you describe a list of actions to take.
You should ensure that your script works with a generic
<filename>sh</filename> and that it does not require
any <filename>bash</filename> or other shell-specific