We all like python for scripting, because it's so much more powerful
than a shell. But sometimes we really need to call a shell command
because it's so much easier than writing yet another library in
python or adding a dependency:

    from whelk import shell
    shell.zgrep("-r", "downloads", "/var/log/httpd")
    # Here goes code to process the log

You can even pipe commands together:

    from whelk import pipe
    pipe(pipe.getent("group") | pipe.grep(":1...:"))
