PLD Linux Distribution

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====== alternatives ======

[[http://linux.die.net/man/8/update-alternatives|update-alternatives]] - maintain symbolic links determining default commands.

Default implementation in PLD Linux is provided by ''alternatives'' package from [[package>chkconfig]].

===== switching alternative =====

By default ''alternatives'' uses ''auto'' mode picking the "best" alternative.

//TODO: how to enforce sysadmin preference//

===== integrating =====

from [[http://git.pld-linux.org/?p=packages/php.git;a=commitdiff;h=82885e7c57e9ee9183eead2319352703c8278a35|phar-php example]]:

<code rpmspec>
Requires:      alternatives
...

%install
...
# touch for ghost
%{__rm} $RPM_BUILD_ROOT%{_bindir}/phar
touch $RPM_BUILD_ROOT%{_bindir}/phar

%post phar
update-alternatives \
       --install %{_bindir}/phar phar %{_bindir}/phar%{ver_suffix}.phar %{ver_suffix} \
       --slave %{_mandir}/man1/phar.1 phar.1 %{_mandir}/man1/phar%{ver_suffix}.1* || :

%postun phar
if [ $1 -eq 0 ]; then
       update-alternatives --remove phar %{_bindir}/phar || :
fi

...
%files
...
%ghost %{_bindir}/phar
%ghost %{_mandir}/man1/phar.1
</code>

  - add ''Requires: alternatives'' to runtime deps
  - the path must be ghost and regular file, otherwise rpm will complin about file-conflicts
  - use ''%%--install%%'' to setup the symlinks in package ''%post'' scriptlet.
  - the ''%%--slave%%'' option is optional and may be repeated, use if you wish to "group" alternatives
  - use proper ''%postun'' to remove alternative on package uninstall

<note warning>
Currently it remains unclear how to handle optional files, as for above example:
  - ''%{_mandir}'' path can be missing if ''%_excludedocs'' is set
  - ''%{_mandir}'' path could be ''.gz'' compressed or not, it's currently solved with a glob: ''%{_mandir}/man1/phar%{ver_suffix}.1*''
</note>
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