Run drush updb in parallel in groups of 5

gistfile1.sh

#!/bin/sh
#
# Run `drush updb` in parallel in groups of 5.
#
# The for loop is populated by running `drush sa`, but this could also be a
# file with aliases on each line.
#
# The

i=0
for site in $(drush sa); do
  echo "---- $site"
  nohup drush @$site updb -y < /dev/null > $HOME/drush-updb.$site.log 2>&1 &
  i=$((i+1))
  if [ 0 -eq $((i%5)) ]; then
    wait
  fi
done