Run a command with exponential backoff, stopping when the command exits with a certain status and (optionally) outputs a specified string

with-backoff

#!/bin/bash

args=$(getopt n:t:r:o: ${*})

if [ $? -ne 0 ] || [ $# -lt 1 ]
  then
  echo "Usage: ${0} [-n=<max-attempts>] [-t=<initial-timeout>] [-r=0] [-o=<output>] <command> <args...>"
  echo "Runs <command> with <args> a maximum of <max-attempts> times until it succeeds.  \"Succeeds\" is"
  echo "defined as returning <r> to the shell (default 0) and printing <output> to the console."
  echo "Waits <initial-timeout> between the first and second attempts, and doubles the timeout each time"
  echo "the command is run"
  exit 2
fi

set -- ${args}

max_attempts=5
timeout=1
output=
return_code=0
for i
  do
  case "$i" in
    -n)
      max_attempts="${2}"; shift; shift;;
    -t)
      timeout="${2}"; shift; shift;;
    -r)
      return_code="${2}"; shift; shift;;
    -o)
      output="${2}"; shift; shift;;
    --)
      shift; break;;
  esac
done

attempt=0
ret=0

while [[ ${attempt} < ${max_attempts} ]]
  do
  out=$("${@}")
  ret=$?

  if [[ ${ret} == ${return_code} && ( -z ${output} || ${out} = ${output} ) ]]
    then
    break
  fi

  sleep ${timeout}
  attempt=$((attempt + 1))
  timeout=$((timeout * 2))
done

echo "${out}"
exit ${ret}