Prevent execution bad commands

Hi All, I am developing a web page where i have to display the files list based on some search criteria and of certain duration. My web server is on linux operating system. The command i am using for this peropse is: find /home/test -mtime -$duration | sort | xargs grep -l "$search_criteria" Is any malicious user can use the search criteria to perform some bad commands in the operating system. If it is then please suggest how to prevent it. Please help me out. Best Regards, Manoj Kumar Singh