Assuming the files are in the current directory, ad that you're using `bash`:

    files=( T*.CDT )
    grep 'FCE-Error' "${files[-1]}"

This would grep the most recent `.CDT` file for the string. You could do the same for the other type of file.

The shell globbing pattern `T*.CDT` expands to all matching filenames sorted lexicographically, and since you are using sane filenames (with proper timestamps that sorts properly), the last of these will be the latest file.

To mail an alert if the string is found:

    files=( T*.CDT )
    if grep -q 'FCE-Error' "${files[-1]}"; then
        mail -s 'Alert' <<END_MESSAGE
    We've found "FCE-Error" in ${files[-1]}, do something!