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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 The basic items that make up a BitBake recipe file are
as follows: as follows:
<itemizedlist> <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> <listitem><para><emphasis>Functions:</emphasis>
Functions provide a series of actions to be performed. Functions provide a series of actions to be performed.
You usually use functions to override the default You usually use functions to override the default
@ -1313,25 +1328,9 @@
new functions are not replacing or complimenting the new functions are not replacing or complimenting the
default functions. default functions.
You can implement functions in Python 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 Both of these options are not seen in the majority of
recipes.</para></listitem> 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> <listitem><para><emphasis>Keywords:</emphasis>
BitBake recipes use only a few keywords. BitBake recipes use only a few keywords.
You use keywords to include common You use keywords to include common
@ -1389,7 +1388,8 @@
</literallayout> </literallayout>
</para></listitem> </para></listitem>
<listitem><para><emphasis>Quote All Assignments: <filename>"&lt;value&gt;"</filename></emphasis> - <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'> <literallayout class='monospaced'>
VAR1 = "${OTHERVAR}" VAR1 = "${OTHERVAR}"
VAR2 = "The version is ${PV}" VAR2 = "The version is ${PV}"
@ -1401,13 +1401,14 @@
unset. unset.
Use the question mark followed by the equal sign Use the question mark followed by the equal sign
(<filename>?=</filename>) to make a "soft" assignment (<filename>?=</filename>) to make a "soft" assignment
used for conditional assignment.</para> used for conditional assignment.
<para>Typically, you use conditional assignment to Typically, "soft" assignments are used in the
provide <filename>local.conf</filename> file for variables
a default value for use when no specific definition is that are allowed to come through from the external
provided by the machine or distro configuration in environment.
your <filename>local.conf</filename> configuration. Doing so allows you to actually set variables from
</para> the external environment that would otherwise be
overwritten.</para>
<para>Here is an example: <para>Here is an example:
<literallayout class='monospaced'> <literallayout class='monospaced'>
VAR1 ?= "New value" VAR1 ?= "New value"
@ -1455,7 +1456,9 @@
This operator does not add any additional space. This operator does not add any additional space.
Also, the operator is applied after all the Also, the operator is applied after all the
<filename>+=</filename>, and <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>
<para>The following example shows the space being <para>The following example shows the space being
explicitly added to the start to ensure the appended explicitly added to the start to ensure the appended
@ -1470,26 +1473,17 @@
<literallayout class='monospaced'> <literallayout class='monospaced'>
SRC_URI_append_sh4 = " file://fix-makefile.patch" SRC_URI_append_sh4 = " file://fix-makefile.patch"
</literallayout> </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> </para></listitem>
<listitem><para><emphasis>Prepending: <filename>_prepend</filename></emphasis> - <listitem><para><emphasis>Prepending: <filename>_prepend</filename></emphasis> -
Use the <filename>_prepend</filename> operator to Use the <filename>_prepend</filename> operator to
prepend values to existing variables. prepend values to existing variables.
This operator does not add any additional space. This operator does not add any additional space.
Also, it is applied after all the This operator does not add any additional space.
<filename>+=</filename> and Also, the operator is applied after all the
<filename>=+</filename> operators have been applied. <filename>+=</filename>, and
<filename>=+</filename> operators have been applied and
after all <filename>=</filename> assignments have
occurred.
</para> </para>
<para>The following example shows the space being <para>The following example shows the space being
explicitly added to the end to ensure the prepended explicitly added to the end to ensure the prepended
@ -1504,45 +1498,29 @@
<literallayout class='monospaced'> <literallayout class='monospaced'>
CFLAGS_prepend_sh4 = " file://fix-makefile.patch" CFLAGS_prepend_sh4 = " file://fix-makefile.patch"
</literallayout> </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${S}/myincludes2 "
</literallayout>
Notice in this example no spacing is used at the
front of the value string.
Recall that the <filename>+=</filename> operator
adds space itself.
</note>
</para></listitem> </para></listitem>
<listitem><para><emphasis>Spaces as Compared to Tabs:</emphasis> <listitem><para><emphasis>Indentation:</emphasis>
Use spaces for indentation rather than than tabs. Use spaces for indentation rather than than tabs.
Both currently work, however it is a policy decision For shell functions, both currently work.
of the Yocto Project to use tabs in shell functions However, it is a policy decision of the Yocto Project
and spaces in Python. to use tabs in shell functions.
However, realize that some layers use a policy of all Realize that some layers have a policy to use spaces
spaces. for all indentation.
</para></listitem> </para></listitem>
<listitem><para><emphasis>Using Python for Complex Operations: <filename>${@...}</filename></emphasis> - <listitem><para><emphasis>Using Python for Complex Operations: <filename>${@&lt;variable&gt;}</filename></emphasis> -
For more advanced processing, it is possible to use For more advanced processing, it is possible to use
Python code during variable assignments (e.g. Python code during variable assignments (e.g.
search and replacement on a variable).</para> search and replacement on a variable).</para>
<para>You indicate Python code using a preceding <para>You indicate Python code using the
<filename>@</filename> character in the variable <filename>${@&lt;variable&gt;}</filename> syntax for the
assignment: variable assignment:
<literallayout class='monospaced'> <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> </literallayout>
</para></listitem> </para></listitem>
<listitem><para><emphasis>Shell Syntax:</emphasis> <listitem><para><emphasis>Shell Function Syntax:</emphasis>
Use shell syntax as if you were writing a shell script Use shell function syntax as if you were writing a shell
when you describe a list of actions to take. script when you describe a list of actions to take.
You should ensure that your script works with a generic You should ensure that your script works with a generic
<filename>sh</filename> and that it does not require <filename>sh</filename> and that it does not require
any <filename>bash</filename> or other shell-specific any <filename>bash</filename> or other shell-specific