diff options
| -rw-r--r-- | bitbake/doc/bitbake-user-manual/bitbake-user-manual-metadata.xml | 25 |
1 files changed, 24 insertions, 1 deletions
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 b8a77e1fa0..5e1a381fac 100644 --- a/bitbake/doc/bitbake-user-manual/bitbake-user-manual-metadata.xml +++ b/bitbake/doc/bitbake-user-manual/bitbake-user-manual-metadata.xml @@ -293,6 +293,17 @@ The flags are immediately set to "abc" and "123", respectively. The <filename>a</filename> flag becomes "abc456". </para> + + <para> + No need exists to pre-define variable flags. + You can simply start using them. + One extremely common application + is to attach some brief documentation to a BitBake variable as + follows: + <literallayout class='monospaced'> + CACHE[doc] = "The directory holding the cache of the metadata." + </literallayout> + </para> </section> <section id='inline-python-variable-expansion'> @@ -306,7 +317,19 @@ DATE = "${@time.strftime('%Y%m%d',time.gmtime())}" </literallayout> This example results in the <filename>DATE</filename> - variable becoming the current date. + variable being set to the current date. + </para> + + <para> + Probably the most common use of this feature is to extract + the value of variables from BitBake's internal data dictionary, + <filename>d</filename>. + The following lines select the values of a package name + and its version number, respectively: + <literallayout class='monospaced'> + PN = "${@bb.parse.BBHandler.vars_from_file(d.getVar('FILE'),d)[0] or 'defaultpkgname'}" + PV = "${@bb.parse.BBHandler.vars_from_file(d.getVar('FILE'),d)[1] or '1.0'}" + </literallayout> </para> </section> |