TIL: timeout in Bash scripts

  $ strace -e trace=clone -e fault=clone:error=EAGAIN

That's for a standard service health check anyway. That service and health check shouldn't be started until the container it depends on has started and is healthy. In Kubernetes that's an Init Container in a Pod, in AWS ECS that's a dependsOn stanza in your Task Container Definition, and for Docker Compose it's the depends_on stanza in a Services entry.

  set -eu
  nowtime="$(date +%s)"
  maxwait=300
  maxloop=5
  c=0
  while [ $c -lt $maxloop ] ; do
      if timeout "$maxwait" curl --silent --fail-with-body 10.0.0.1:8080/health ; then
          exit 0
      else
          sleep 1
      fi
      if [ "$(date +%s)" -gt "$((nowtime+maxwait))" ] ; then
          echo "$0: Error: max wait time $maxwait exceeded"
          exit 1
      fi
      c=$((c+1))
  done

  curl --silent --fail-with-body --connect-timeout 5 --retry-all-errors --retry-delay 1 --retry-max-time 300 --retry 300 10.0.0.1:8080/health

I haven’t quite been able to do it using _only_ builtins, but if you allow the sleep command (which has been standardised since the first version of POSIX, so it should be available pretty much anywhere that makes any sort of attempt to be POSIX compliant), then this seems ok:

  # TIMEOUT SYSTEM
  #
  # Defines a timeout function:
  #
  # Usage: timeout <num_seconds> <command>
  #
  # which runs <command> after <num_seconds> have elapsed, if the script
  # has not exited by then.

  _alarm() {
      local timeout=$1

      # Spawn a subshell that sleeps for $timeout seconds
      # and then sends us SIGALRM
      (
          sleep "$timeout"
          kill -ALRM $$
      ) &

      # If this shell exits before the timeout has fired,
      # clean up by killing the subshell
      subshell_pid=$!
      trap _cleanup EXIT
  }

  _cleanup() {
      if [ -n "$subshell_pid" ]
      then
          kill "$subshell_pid"
      fi
  }

  timeout() {
      local timeout=$1
      local command=$2

      trap "$command" ALRM
      _alarm "$timeout"
  }

  # MAIN PROGRAM

  times_up() {
      echo 'TIME OUT!'
      subshell_pid=
      exit 1
  }

  timeout 10 times_up

  for i in {1..20}
  do
      sleep 1
      echo $i
  done

   bash -c 'some command "$1" "$2"' -- "$var1" "$var2"

Note that bash specifically has printf %q which could alternatively be used, but I prefer to use bourne-compatible things when the bash version isn't significantly cleaner.

    timeout 1800 mplayer show.mp4 ; sudo pm-suspend

     for i in {0..60}; do
         true -- "$i" # shelleck surpression
         if eventually_succeeds; then break; fi
         sleep 1s
     done

    #!/usr/bin/env bash

    long_fn () { # this can contain anything, like OPs until curl loop
      sleep $1
    }

    # to TIMEOUT_DURATION BASH_FN_NAME BASH_FN_ARGS...
    to () {
      local duration="$1"; shift
      local fn_name="$1"; shift
      export -f "$fn_name"
      timeout "$duration" bash -c "$fn_name"'  "$@"' _ $@
    }

    time to 1s long_fn 5 # will report it ran 1 second

https://github.com/vegardit/await.sh

  #!/usr/bin/env bash
  
  runUntilDoneOrTimeout () {
      local -i timeout=0
      OPTIND=1
      while getopts "t:" opt; do
          case $opt in
              t) timeout=$OPTARG;;
          esac
      done
      shift $((OPTIND - 1))
      runCommand="$*"
      $runCommand &
      runPID=$!
      echo checking jobs
      jobs # just to prove there are some
      echo job check complete
      while jobs %- >& /dev/null && ((timeout > 0)); do
          echo "waiting for $runCommand for $timeout seconds"
          sleep 1
          ((timeout--))
      done
      if (( timeout == 0 )); then
          echo "$runCommand timed out"
          kill -9 $runPID
          wait $runPID
      else
          echo "$runCommand completed"
      fi
      echo checking jobs
      jobs # just to prove there are none
      echo job check complete
  }
  
  declare -i timeopt=10
  declare -i sleepopt=100
  OPTIND=1
  while getopts "t:s:" opt; do
      case $opt in
          t) timeopt=$OPTARG;;
          s) sleepopt=$OPTARG;;
      esac
  done
  shift $((OPTIND - 1))
  runUntilDoneOrTimeout -t $timeopt sleep $sleepopt

   timeout 5 bash -c 'cat < /dev/null > /dev/tcp/google.com/80'

It’s more useful if you are implementing this in a general programming language, not in the shell, or if you want to know how it works under the hood.

You dont need to timeout here, and you won't need to subshell another bash to just get the timeout to work.

This is very complex, because if you.write lots of functions that call functions, you really just want to run something that inherits while env from your process, that's why there is control and sleep process and naive race to decide which finished first...

That's probably reason I ignored built-in timeout...

Is there an attempt anywhere to build a slightly modern standard library for bash scripts?

You know besides stack overflow?

That saves you a whole character of typing:

  until command ; do ... done

  -->

  while ! command; do ... done

https://github.com/minfrin/retry

    --connect-timeout <seconds>

    --retry <num>

    curl --retry 5 --connect-timeout 10

Been working flawlessly since 20 years: so flawlessly that I don't remember how it works.