i have a script to look for a file, but it moves a file that's being used.

i want to use:

if file exists > 0, and not being updated/used in the last 2 minutes, move to /tmp

i can do this much:

if [ -s filename.txt ]
then
mv filename.txt /tmp
else
exit
fi

or how can i check if filename.txt is being used ?

lsof or fuser will show if a file is open. You may have one or both on your system.

or If you need to check if a file's updated in the last x minutes whether it's open or not, you could maybe pipe output from
ls -l <file>
into a grep command to get the time, and check if that's in the last x minutes. (Not sure of the quickest way to do that right now)

fuser does the trick. thanks for your direction.