This should work if your file names have no embedded spaces:
for file in /foo/*
do
  if [ -f $file ]
  then
    dd if=$file of=$file.truncated bs=31 skip=1 && mv $file.truncated $file
  fi
done
This should work if your file names have no embedded spaces:
for file in /foo/*
do
  if [ -f $file ]
  then
    dd if=$file of=$file.truncated bs=31 skip=1 && mv $file.truncated $file
  fi
done