cp(1) %22%24%28ls -t *.txt %7C head -n 1%29%22 %2Fbackup
copy files and directories
Copy SOURCE to DEST, or multiple SOURCE(s) to DIRECTORY.
-t, --target-directory=DIRECTORY
       copy all SOURCE arguments into DIRECTORY
-n, --no-clobber
       do not overwrite an existing file (overrides a previous -i option)
source manpages: cp