Here is a command to create a temporary directory for your user that will hold files for 90 days since their last modification date:

mkdir ~/tmp
chmod 700 ~/tmp

find ~/tmp -type f -mtime +90 -delete

This will:

• Create a directory called ~/tmp owned by your user
• Set permissions on it so only you have access
• Run find daily to delete any files older than 90 days inside the ~/tmp directory

To automate the find command, you can add it to your crontab by running:

crontab -e

And adding:

0 0 * * * find ~/tmp -type f -mtime +90 -delete

This will run the find command every day at midnight to clean up files older than 90 days in ~/tmp.

The ~/tmp directory will now persist and hold files for 90 days since their last modification date before being automatically deleted.