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@sj26

sj26/LICENSE.md

Last active Dec 29, 2022

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Bash retry function
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LICENSE.md

This is free and unencumbered software released into the public
domain.

Anyone is free to copy, modify, publish, use, compile, sell, or
distribute this software, either in source code form or as a compiled
binary, for any purpose, commercial or non-commercial, and by any
means.

In jurisdictions that recognize copyright laws, the author or authors
of this software dedicate any and all copyright interest in the
software to the public domain. We make this dedication for the
benefit of the public at large and to the detriment of our heirs and
successors. We intend this dedication to be an overt act of
relinquishment in perpetuity of all present and future rights to this
software under copyright law.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY
CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

For more information, please refer to https://unlicense.org

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retry.sh
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 # Retry a command up to a specific numer of times until it exits
 successfully,
 # with exponential back off.
 #
 # $ retry 5 echo Hello
 # Hello
 #
 # $ retry 5 false
 # Retry 1/5 exited 1, retrying in 1 seconds...
 # Retry 2/5 exited 1, retrying in 2 seconds...
 # Retry 3/5 exited 1, retrying in 4 seconds...
 # Retry 4/5 exited 1, retrying in 8 seconds...
 # Retry 5/5 exited 1, no more retries left.
 #
 function retry {
 local retries=$1
 shift
 local count=0
 until "$@"; do
 exit=$?
 wait=$((2 ** $count))
 count=$(($count + 1))
 if [ $count -lt $retries ]; then
 echo "Retry $count/$retries exited $exit, retrying in $wait
 seconds..."
 sleep $wait
 else
 echo "Retry $count/$retries exited $exit, no more retries left."
 return $exit
 fi
 done
 return 0
 }

@ronronshaiko
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ronronshaiko commented Sep 5, 2019

Great function !! thanks

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@hughsaunders
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hughsaunders commented Oct 8, 2019 *
edited

Thanks, going to include this in https://github.com/cyberark/bash-lib
, hope you don't mind :)

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@gtarnaras
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gtarnaras commented Oct 16, 2019

Thanks for sharing!

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@hunter-richardson
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hunter-richardson commented Oct 16, 2019 *
edited

Translated to fish (using printf instead of echo) with the
humanize_duration function:

#!/usr/bin/fish
function retry -d 'Retry a command up to a specified number of times, until it exits successfully'
  if test (count $argv) -lt 2; or string match -irqv '^[0-9]+$' $argv[1]
    printf 'Proper use: %s [number of attempts until giving up] [command to attempt]\n' (status function);
    return 23
  else
    set -l retries $argv[1]
    set -l command (string split -m 1 ' ' "$argv")[2];
      and printf 'eval %s\n' (printf '%s ' $command)
    for i in (seq $retries)
      eval $command
      set -l cmd_status $status
      if test $cmd_status -eq 0
        printf 'Try #%d of %d succeeded.\n' $i $retries
        return 0
      else if test $i -eq $retries
        set -l exit $status
        printf 'Final try #%d exited %d.\n' $i $cmd_status
        return $cmd_status
      else
        set -l wait (math "2 ^ ($i - 1)")
        printf 'Try #%d of %d exited %d, retrying in %s...\n\n' $i $retries $cmd_status (math "1000 * $wait" | humanize_duration)
        sleep $wait
      end
    end
  end
end

Available here.

Examples:

$ retry a echo Hello
Proper use: retry [number of attempts before giving up] [command to attempt]
#  exit code 23

$ retry 5
Proper use: retry [number of attempts before giving up] [command to attempt]
#  exit code 23

$ retry 8 false
eval false
Try #1 of 8 exited 1, retrying in 1s...
Try #2 of 8 exited 1, retrying in 2s...
Try #3 of 8 exited 1, retrying in 4s...
Try #4 of 8 exited 1, retrying in 8s...
Try #5 of 8 exited 1, retrying in 16s...
Try #6 of 8 exited 1, retrying in 32s...
Try #7 of 8 exited 1, retrying in 1m 4s...
Final try #8 exited 1.
#  exit code 1

$ retry 5 echo Hello
eval echo Hello
Hello
Try #1 of 5 succeeded.
#  exit code 0

$ retry 5 ping -n -1 -w 1 google.com
eval ping -n 1 -w 1 google.com

Pinging google.com [172.217.164.174] with 32 bytes of data:
Request timed out.

Ping statistics for 172.217.164.174:
    Packets: Send =1, Received = 0, Lost = 1 (100% loss),
Try #1 of 5 exited 1, retrying in 1s...

Pinging google.com [172.217.164.174] with 32 bytes of data:
Reply from 172.217.164.174:  bytes=32 time=30ms TTL=55

Ping statistics for 172.217.164.174:
    Packets: Sent = 1, Received = 1, Lost = 0 (0% loss)
Approximate round trip times in milliseconds:
    Minimum = 30ms, Maximum = 30ms, Average = 30ms
Try #2 of 5 succeeded.
#  exit code 0

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@ypid
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ypid commented Nov 17, 2019 *
edited

Well done! I hope you don't mind, I am using it in hashbang/
aosp-build#8. I reworked it a bit so that it passes ShellCheck.

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@valm13
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valm13 commented May 27, 2021

Thanks, it's very useful and easy to use!

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@hcharley
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hcharley commented May 4, 2022

This is the full bash file I use to be able to call the file with the
same args as the function fwiw:

#!/bin/bash

function retry {
  local retries=$1
  shift

  local count=0
  until "$@"; do
    exit=$?
    wait=$((2 ** $count))
    count=$(($count + 1))
    if [ $count -lt $retries ]; then
      echo "Retry $count/$retries exited $exit, retrying in $wait seconds..."
      sleep $wait
    else
      echo "Retry $count/$retries exited $exit, no more retries left."
      return $exit
    fi
  done
  return 0
}

retry $@

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@jakub-bochenski
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jakub-bochenski commented May 13, 2022

@hcharley just define the function in your .bashrc or whatnot and you
will be able to call it directly

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@albertvaka
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albertvaka commented Sep 2, 2022

What's the license of this code?

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@sj26
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Author

sj26 commented Sep 5, 2022

It didn't have one, but I'm happy to pop it under MIT, and have added
a license file.

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@cmedved
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cmedved commented Dec 8, 2022

Personally, I much preferred it without a license, because now I
can't use it without copying that chunk of text into my script above
the function... which is a bit excessive.

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@sj26
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Author

sj26 commented Dec 8, 2022

Fair point, I don't really care about the license notice being
preserved. Unlicensed.

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@ypid
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ypid commented Dec 12, 2022

https://reuse.software/ comes to the rescue. You can drop that
license file (at least for this small script probably the easiest) or
let the reuse tool manage it. Than add something like this to the top
of the file:

# SPDX-FileCopyrightText: 2016, 2018-2019 Jane Doe <jane@example.com>
#
# SPDX-License-Identifier: GPL-3.0-or-later

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@corneliusroot
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corneliusroot commented Dec 28, 2022

Excellent function. Used it in a watchdog script, helps avoid false
alarms due to initial time-outs. Thanks for publishing this!

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