How to execute command every 10 seconds (without cron)?

To access your personal cron configuration you should use the command crontab -e (to edit your cron table).

Alternative is the watch command:

watch -n10 command args

Finally, to monitor filesystem events more effectively, you could use inotifywait, from inotify-tools package.

You can write a shell script that has sleep in a while loop.

#!/bin/sh
while [ true ]
do
    sh special_svn_script.sh
    sleep 10
done

gnome-schedule (click the button to Install now! using your Software Center)
is a graphical user interface that leverages the power of vixie-cron, dcron and at to manage your crontab file and provide an easy way to schedule tasks on your computer. It supports recurrent (periodical) tasks and tasks that happen only once in the future. It is written in Python using pygtk.

Awesome features

• Supports custom titles and icons for your tasks so that they are more easily to keep track of
• Templates support so that you won't have to create the same task again and again; these are saved in gconf and may easily ship them with, say, a Linux distribution
• If run as root, you can edit any user's crontab and "at" tasks.
• Human-readable strings like "Every hour" instead of "0 * * * *"
• Advanced mode for crontab experts
• Provides a "panel applet" where you can manage tasks from a dropdown menu
• Predefined common expressions like: every minute, every week, tomorrow, next week A calendar allows you to choose the day you want a task executed