Find the smallest file
Bash + coreutils, 13 bytes
ls -Sar|sed q

Explanation:
ls -Sar|sed q
ls            # list files
   -S         # sorted, biggest first
     a        # show hidden files
      r       # reversed (smallest first)
       |sed q # q is quit at first line that matches given regex, 
              # given regex is empty so guaranteed match.