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-rw-r--r--bitbake/doc/bitbake-user-manual/bitbake-user-manual-metadata.xml72
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diff --git a/bitbake/doc/bitbake-user-manual/bitbake-user-manual-metadata.xml b/bitbake/doc/bitbake-user-manual/bitbake-user-manual-metadata.xml
index 199ab23095..a125ad332e 100644
--- a/bitbake/doc/bitbake-user-manual/bitbake-user-manual-metadata.xml
+++ b/bitbake/doc/bitbake-user-manual/bitbake-user-manual-metadata.xml
@@ -61,6 +61,78 @@
61 </para> 61 </para>
62 </section> 62 </section>
63 63
64 <section id='modifying-existing-variables'>
65 <title>Modifying Existing Variables</title>
66
67 <para>
68 Sometimes you need to modify existing variables.
69 Following are some cases where you might find you want to
70 modify an existing variable:
71 <itemizedlist>
72 <listitem><para>
73 Customize a recipe that uses the variable.
74 </para></listitem>
75 <listitem><para>
76 Change a variable's default value used in a
77 <filename>*.bbclass</filename> file.
78 </para></listitem>
79 <listitem><para>
80 Change the variable in a <filename>*.bbappend</filename>
81 file to override the variable in the original recipe.
82 </para></listitem>
83 <listitem><para>
84 Change the variable in a configuration file so that the
85 value overrides an existing configuration.
86 </para></listitem>
87 </itemizedlist>
88 </para>
89
90 <para>
91 Changing a variable value can sometimes depend on how the
92 value was originally assigned and also on the desired
93 intent of the change.
94 In particular, when you append a value to a variable that
95 has a default value, the resulting value might not be what
96 you expect.
97 In this case, the value you provide might replace the value
98 rather than append to the default value.
99 </para>
100
101 <para>
102 If after you have changed a variable's value and something
103 unexplained occurs, you can use BitBake to check the actual
104 value of the suspect variable.
105 You can make these checks for both configuration and recipe
106 level changes:
107 <itemizedlist>
108 <listitem><para>
109 For configuration changes, use the following:
110 <literallayout class='monospaced'>
111 $ bitbake -e
112 </literallayout>
113 This command displays variable values after the
114 configuration files (i.e. <filename>local.conf</filename>,
115 <filename>bblayers.conf</filename>,
116 <filename>bitbake.conf</filename> and so forth) have
117 been parsed.
118 <note>
119 Variables that are exported to the environment are
120 preceded by the string "export" in the command's
121 output.
122 </note>
123 </para></listitem>
124 <listitem><para>
125 For recipe changes, use the following:
126 <literallayout class='monospaced'>
127 $ bitbake <replaceable>recipe</replaceable> -e | grep VARIABLE="
128 </literallayout>
129 This command checks to see if the variable actually
130 makes it into a specific recipe.
131 </para></listitem>
132 </itemizedlist>
133 </para>
134 </section>
135
64 <section id='line-joining'> 136 <section id='line-joining'>
65 <title>Line Joining</title> 137 <title>Line Joining</title>
66 138