retry.sh

#!/usr/bin/env sh

usage() {
  cat <<-EOM
USAGE: `basename $0` <max_retries> <command> [<param1> [<param2> [...] ] ]

  Retry shell commands until they work or max retries has been reached.

  Helpful in a long running automation pipeline where a single non-zero
  return status can waste a lot of time.

  [Everything is just terrible, maybe we can mask it and pretend not.]

  Example:
  retry.sh 10 apk --no-cache add tini
EOM
  exit 1
}

fail() {
  echo $@
  exit 2
}

if [ $# -lt 2 ] ; then
  usage
fi

retries=$1
shift
command=$@
bin=$(echo $command | awk '{print $1}')
[ -x `which ${bin}` ] || fail "ERROR $bin is not executable for this user (maybe it doesn't exist?)"

echo "Running \`$command\` with $retries retries"

n=0
while true
do
  $command && break
  n=$(expr $n + 1)
  if [ $n -le $retries ] ; then
    echo "Retry # $n"
  else
    fail "ERROR: Max retries. Unable to \`$command\`"
  fi
  sleep 5
done