touch [OPTION]... FILE...
touch updates the access and modification times of each FILE to the current time.
Allows you to 'touch' a file. Can be used to create an empty file or update the access/modification times on an existing file. It also has the less well-known ability of allowing you to set a file's modification times to any time you like - handy for covering your tracks...
Create an empty file
Update the modification/access times on an exiting file
Set the times of a file to the specified time, past or future
# Date format is [[CC]YY]MMDDhhmm[.ss] $ touch ripley $ ls -l ripley -rw-r--r-- 1 garry garry 0 2010-11-07 23:58 ripley $ touch -t 200512250600 ripley $ ls -l ripley -rw-r--r-- 1 garry garry 0 2005-12-25 06:00 ripley