Bash retry function

LICENSE.md

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retry.sh

# 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
}

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

What's the license of this code?

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

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.

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

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 <[email protected]>
#
# SPDX-License-Identifier: GPL-3.0-or-later

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

Perhaps localize $wait and $exit, too ?

One improvement would be to log to stderr instead of stdout - e.g.:
echo "Retry $count/$retries exited $exit, retrying in $wait seconds..." >&2