How to run some Ant target only once ?

    <target name="show-info" unless="show-info_has_run">
        <property name="show-info_has_run" value="true"/>

        <!-- ...... some actions --- ->

    </target>

Reminders for Magento developer (part 1)

Check if logging is enabled on your development environment: option 'System->Configuration->Advanced:Developer->Log Settings->Enabled' should be 'Yes'

If you get some errors in layout xml files they will be written to 'var/log/exception.log' and 'var/log/system.log' files.

How to redirect output to stdout and stderr to files ?

some_command >>file.stdout.txt 2>>file.stderr.txt