How do I write a retry logic in script to keep retrying to run it upto 5 times?

Question

I want to write logic in shell script which will retry it to run again after 15 sec upto 5 times based on "status code=FAIL" if it fails due to some issue.

Answer 1

This script uses a counter n to limit the attempts at the command to five. If the command is successful, $? will hold zero and execution will break from the loop.

   n=0
   until [ $n -ge 5 ]
   do
      command && break  # substitute your command here
      n=$[$n+1]
      sleep 15
   done

Answer 2

for i in 1 2 3 4 5; do command && break || sleep 15; done

Replace "command" with your command. This is assuming that "status code=FAIL" means any non-zero return code.

---

Variations:

Using the {..} syntax. Works in most shells, but not BusyBox sh:

for i in {1..5}; do command && break || sleep 15; done

Using seq and passing along the exit code of the failed command:

for i in $(seq 1 5); do command && s=0 && break || s=$? && sleep 15; done; (exit $s)

Same as above, but skipping sleep 15 after the final fail. Since it's better to only define the maximum number of loops once, this is achieved by sleeping at the start of the loop if i > 1:

for i in $(seq 1 5); do [ $i -gt 1 ] && sleep 15; command && s=0 && break || s=$?; done; (exit $s)

Answer 3

function fail {
  echo $1 >&2
  exit 1
}

function retry {
  local n=1
  local max=5
  local delay=15
  while true; do
    "$@" && break || {
      if [[ $n -lt $max ]]; then
        ((n++))
        echo "Command failed. Attempt $n/$max:"
        sleep $delay;
      else
        fail "The command has failed after $n attempts."
      fi
    }
  done
}

Example:

retry ping invalidserver

produces this output:

ping: unknown host invalidserver
Command failed. Attempt 2/5:
ping: unknown host invalidserver
Command failed. Attempt 3/5:
ping: unknown host invalidserver
Command failed. Attempt 4/5:
ping: unknown host invalidserver
Command failed. Attempt 5/5:
ping: unknown host invalidserver
The command 'ping invalidserver' failed after 5 attempts

For a real-world, working example with complex commands, see this script.

Answer 4

Here is function for retry

function retry()
{
        local n=0
        local try=$1
        local cmd="${@: 2}"
        [[ $# -le 1 ]] && {
        echo "Usage $0 <retry_number> <Command>"; }

        until [[ $n -ge $try ]]
        do
                $cmd && break || {
                        echo "Command Fail.."
                        ((n++))
                        echo "retry $n ::"
                        sleep 1;
                        }

        done
}

retry $*

Output :

[test@Nagios ~]$ ./retry.sh 3 ping -c1 localhost
PING localhost (127.0.0.1) 56(84) bytes of data.
64 bytes from localhost (127.0.0.1): icmp_seq=1 ttl=64 time=0.207 ms

--- localhost ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 0.207/0.207/0.207/0.000 ms

[test@Nagios ~]$ ./retry.sh 3 ping -c1 localhostlasjflasd
ping: unknown host localhostlasjflasd
Command Fail..
retry 1 ::
ping: unknown host localhostlasjflasd
Command Fail..
retry 2 ::
ping: unknown host localhostlasjflasd
Command Fail..
retry 3 ::

Answer 5

Here is my favorite one line alias / script

    alias retry='while [ $? -ne 0 ] ; do fc -s ; done'

Then you can do stuff like:

     $ ps -ef | grep "Next Process"
     $ retry

and it will keep running the prior command until it finds "Next Process"

Answer 6

I use this script that makes the retries of a given command, the benefit of this script is that if fails all retries it will preserve the exit code.

#!/usr/bin/env bash

if [ $# -ne 3 ]; then
    echo 'usage: retry <num retries> <wait retry secs> "<command>"'
    exit 1
fi

retries=$1
wait_retry=$2
command=$3

for i in `seq 1 $retries`; do
    echo "$command"
    $command
    ret_value=$?
    [ $ret_value -eq 0 ] && break
    echo "> failed with $ret_value, waiting to retry..."
    sleep $wait_retry
done

exit $ret_value

Probably it can get simplier

Answer 7

See below Example :

n=0
while :
do
        nc -vzw1 localhost 3859
        [[ $? = 0 ]] && break || ((n++))
        (( n >= 5 )) && break

done

I'm trying to connect port 3389 on localhost, it will retry until 5 times fail , if success then it will break the loop.

$? it's exist status of command if it zero means command successfully run , if other than zero means command fai

Seems little bit complicated, may be someone do it better than this.

Answer 8

You can use the loop command, available here, like so:

$ loop './do_thing.sh' --every 15s --until-success --num 5 

Which will do your thing every 15 seconds until it succeeds, for a maximum of five times.

Answer 9

Here's a recursive retry function for functional programming purists:

retry() {
  cmd=$1
  try=${2:-15}       # 15 by default
  sleep_time=${3:-3} # 3 seconds by default

  # Show help if a command to retry is not specified.
  [ -z "$1" ] && echo 'Usage: retry cmd [try=15 sleep_time=3]' && return 1

  # The unsuccessful recursion termination condition (if no retries left)
  [ $try -lt 1 ] && echo 'All retries failed.' && return 1

  # The successful recursion termination condition (if the function succeeded)
  $cmd && return 0

  echo "Execution of '$cmd' failed."

  # Inform that all is not lost if at least one more retry is available.
  # $attempts include current try, so tries left is $attempts-1.
  if [ $((try-1)) -gt 0 ]; then
    echo "There are still $((try-1)) retrie(s) left."
    echo "Waiting for $sleep_time seconds..." && sleep $sleep_time
  fi

  # Recurse
  retry $cmd $((try-1)) $sleep_time
}

Pass it a command (or a function name) and optionally a number of retries and a sleep duration between retries, like so:

retry some_command_or_fn 5 15 # 5 tries, sleep 15 seconds between each