diff options
Diffstat (limited to 'bitbake/doc/manual/usermanual.xml')
| -rw-r--r-- | bitbake/doc/manual/usermanual.xml | 8 |
1 files changed, 7 insertions, 1 deletions
diff --git a/bitbake/doc/manual/usermanual.xml b/bitbake/doc/manual/usermanual.xml index c3403449fe..450ac77d7a 100644 --- a/bitbake/doc/manual/usermanual.xml +++ b/bitbake/doc/manual/usermanual.xml @@ -91,7 +91,13 @@ share common metadata between many packages.</para></listitem> <section> <title>Setting a default value (?=)</title> <para><screen><varname>A</varname> ?= "aval"</screen></para> - <para>If <varname>A</varname> is set before the above is called, it will retain it's previous value. If <varname>A</varname> is unset prior to the above call, <varname>A</varname> will be set to <literal>aval</literal>.</para> + <para>If <varname>A</varname> is set before the above is called, it will retain it's previous value. If <varname>A</varname> is unset prior to the above call, <varname>A</varname> will be set to <literal>aval</literal>. Note that this assignment is immediate, so if there are multiple ?= assignments to a single variable, the first of those will be used.</para> + </section> + <section> + <title>Setting a default value (??=)</title> + <para><screen><varname>A</varname> ??= "somevalue"</screen></para> + <para><screen><varname>A</varname> ??= "someothervalue"</screen></para> + <para>If <varname>A</varname> is set before the above, it will retain that value. If <varname>A</varname> is unset prior to the above, <varname>A</varname> will be set to <literal>someothervalue</literal>. This is a lazy version of ??=, in that the assignment does not occur until the end of the parsing process, so that the last, rather than the first, ??= assignment to a given variable will be used.</para> </section> <section> <title>Immediate variable expansion (:=)</title> |