160

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.

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14 Answers 14

144

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
3
  • could you explain about command here?? does it mean command to run the script – Sandeep Singh Jul 11 '13 at 12:45
  • 1
    "command" is just the name of the command that you want to check the status of. – suspectus Jul 11 '13 at 13:00
  • 3
    Worth noting that you can test if n equals five at the end to know if command succeeded or not. – mattdm Dec 23 '15 at 14:20
184
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)
3
  • 9
    Just a note, this works because the && is evaluated before the || because of operator precedence – gene_wood Sep 4 '15 at 19:50
  • Shellcheck says: "Note that A && B || C is not if-then-else. C may run when A is true. [SC2015]" – Mausy5043 Dec 29 '18 at 10:25
  • 1
    @Mausy5043, for this case it does not matter, since s=0 is true, and break breaks the loop. – Alexander Mar 2 '19 at 17:30
46
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.

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19

GNU Parallel has --retries:

parallel --retries 5 --delay 15s ::: ./do_thing.sh

Example:

parallel -t --retries 5 --delay 0.1s 'echo {};exit {}' ::: {0..10}
6
  • This doesn't work. --retries is for retries on different machines: "If a job fails, retry it on another computer on which it has not failed. Do this n times. If there are fewer than n computers in --sshlogin GNU parallel will re-use all the computers. This is useful if some jobs fail for no apparent reason (such as network failure)" – James Moore May 8 '20 at 16:31
  • 1
    Have you tested? --retries is both for local and remote jobs. But for remote jobs GNU Parallel tries to retry the job on another server if possible (maybe this job and that server just do not like eachother for some unknown reason). – Ole Tange May 8 '20 at 16:45
  • Turns out I was confused by the documentation and by one undocumented feature (at least I didn't see doc) of retries - if you fail, and you have retries turned on, you don't see stderr until the last fatal error. – James Moore May 8 '20 at 18:07
  • The --help of parallel could be better. In general it's a nicely developed tool, certainly superior to the alternatives with a few minor downsides. (At least since the citation nagscreen is gone, that was a no-go for me.) Btw: --delay is not delaying only for retries, it delays everything. afaik there is no functionality yet to delay only on error (would be useful – John Jan 7 at 4:21
  • @john You should feel free to submit at bug report with a better --help text. savannah.gnu.org/bugs/?func=additem&group=parallel Version 20201222 has --delay 123auto which will start out at 123, but adjust the delay up and down depending on whether jobs succeed or fail. – Ole Tange Jan 7 at 12:58
12

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 ::
5
  • I copy pasted your code in a new file called retry.sh and added a line #!/bin/bash at the top. While running with your given commands in the explanation I don't see anything just prompt comes again. – java_enthu Aug 19 '13 at 10:54
  • have you tried bash retry.sh 3 ping -c1 localhost – Rahul Patil Aug 19 '13 at 11:26
  • Yes Rahul I did try. – java_enthu Aug 19 '13 at 11:29
  • Sorry, I was bizy.., I have tested again, it's working , check output paste.ubuntu.com/6002711 – Rahul Patil Aug 19 '13 at 12:35
  • this is the most elegant answer in here so far--if you're doing something non-trivial. Thanks for taking the time. – Jerry Andrews May 8 '19 at 17:42
12

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"

2
  • 3
    In zsh, use fc -e "#" instead of fc -s. – Ricardo Stuven Aug 17 '17 at 14:55
  • Very cool oneliner! @RicardoStuven thanks for fc -e "#" - it works in bash too. – Noam Manos Apr 28 '20 at 10:15
4

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.

3

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.

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  • Thanks rahul.. will it be keep retry to run the script ?? – Sandeep Singh Jul 11 '13 at 7:28
  • Please check now, I have updated – Rahul Patil Jul 11 '13 at 7:32
  • $? it's exist status of command if it zero means command successfully run , if other than zero means command fail – Rahul Patil Jul 11 '13 at 7:34
  • is it required to give host and port address. can we do it by giving script location dir only. – Sandeep Singh Jul 11 '13 at 7:43
  • replace with any command that give exit status code $? – Rahul Patil Jul 11 '13 at 7:44
3

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

4
  • I like how flexible this version is and how verbose and readable the code is! – yo.ian.g Jan 6 '17 at 12:43
  • To match the failed echo you could even add a succeeded echo with the [ $ret_value -eq 0 ] or testing the $ret_value afterwards – yo.ian.g Jan 6 '17 at 12:49
  • not work if cmd like mysql -uroot -pxxxx -e 'DROP DATABASE xxx' – wyx Jul 8 '20 at 2:39
  • try to put your cmd between " – padilo Jul 8 '20 at 15:00
3

Having a need to do this multiple times, the scripting was getting out of hand, so I created a dedicated tool for this called retry.

retry --until=success --times=5 --delay=15 command ...

Retry is available here: https://github.com/minfrin/retry

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  • I like how the tool is conscious that it might be run in a pipeline that expects the command to run just once. Well done. – Wayne Conrad May 7 '20 at 13:21
0

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
1
  • This doesn't work for commands more than one word long: cmd="echo blah blah" ... line 10: [: blah: integer expression expected ... Neither does it work for pipes, etc. – Mercury00 Mar 14 '19 at 18:05
0

Answering this question as existing answers fail to,

  1. Doesn't throw Error Code.
  2. By doing exit errCode, Bash doesn't honor certain traps such as trap somefunc ERR
COMMAND="SOMECOMMAND"
TOTAL_RETRIES=3

retrycount=0
until [ $retrycount -ge $((TOTAL_RETRIES-1)) ]
do
   $COMMAND && break
   retrycount=$((retrycount+1))
   sleep 1
done

if [ $retrycount -eq $((TOTAL_RETRIES-1)) ]
then
    $COMMAND
fi
0
    # Retries a given command given number of times and outputs to given variable
    # $1 : Command to be passed : handles both simple, piped commands
    # $2 : Final output of the command(if successfull)
    # $3 : Number of retrial attempts[Default 5]
    function retry_function() {
        echo "Command to be executed : $1"
        echo "Final output variable : $2"
        echo "Total trials [Default:5] : $3"
        counter=${3:-5}
        local _my_output_=$2 #make sure passed variable is not same as this
        i=1
        while [ $i -le $counter ]; do
            local my_result=$(eval "$1")
            # this tests if output variable is populated and accordingly retries,
            # Not possible to provide error status/logs(STDIN,STDERR)-owing to subshell execution of command
            # if error logs are needed, execute the same code, outside function in same shell
            if test -z "$my_result"
            then
                echo "Trial[$i/$counter]: Execution failed"
            else
                echo "Trial[$i/$counter]: Successfull execution"
                eval $_my_output_="'$my_result'"
                break
            fi
            let i+=1
        done
    }

    retry_function "ping -c 4 google.com | grep \"min/avg/max\" | awk -F\"/\" '{print \$5}'" avg_rtt_time
    echo $avg_rtt_time

 - To pass in a lengthy command, pass a method echoing the content. Take care of method expansion accordingly in a subshell at appropriate place.
 - Wait time can be added too - just before the increment!
 - For a complex command, youll have to take care of stringifying it(Good luck)
0

This is an old question but I found myself returning to this often. My use case was to have a one liner that can retry a command up to n times that can be used on with kubernetes pod (of course if it will work for bash script).

TRY=6; until [ $TRY -eq 0 ] || <your command over here> ; do echo $TRY; echo "<output message>"; TRY=$(expr $TRY - 1); sleep 15; done;

The one liner is a bit hard to get your head around, but it can be very helpful.

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