Retry a shell command on failure, with optional exponential backoff. Bash 3 compatible, works on vanilla macOS.

retry.sh

#!/usr/bin/env bash
set -euo pipefail

if [[ -t 2 ]]; then
  RED='\033[0;31m'; GREEN='\033[0;32m'; NC='\033[0m'
else
  RED=''; GREEN=''; NC=''
fi

# Defaults
MAX_RETRIES=0        # 0 = unlimited
BACKOFF=false
BACKOFF_MAX=30
DELAY=1

usage() {
  cat >&2 <<EOF
Usage: retry [OPTIONS] -- COMMAND [ARGS...]

Options:
  -n, --retries N       Max retries (default: unlimited)
  -b, --backoff         Enable exponential backoff (default: off)
  -d, --delay N         Base delay in seconds (default: 1)
  -m, --max-delay N     Max backoff delay in seconds (default: 30)
  -h, --help            Show this help
EOF
}

while [[ $# -gt 0 ]]; do
  case "$1" in
    -n|--retries)   MAX_RETRIES="$2"; shift 2 ;;
    -b|--backoff)   BACKOFF=true; shift ;;
    -d|--delay)     DELAY="$2"; shift 2 ;;
    -m|--max-delay) BACKOFF_MAX="$2"; shift 2 ;;
    -h|--help)      usage; exit 0 ;;
    --)             shift; break ;;
    *)              break ;;
  esac
done

[[ $# -eq 0 ]] && { echo -e "Error: no command specified\n" >&2; usage; exit 1; }

attempt=0

while true; do
  if "$@"; then
    [[ $attempt -gt 0 ]] && { echo >&2; echo -e "${GREEN}✓${NC} Succeeded on attempt $((attempt + 1))" >&2; }
    exit 0
  fi

  exit_code=$?
  attempt=$((attempt + 1))

  if [[ $MAX_RETRIES -gt 0 && $attempt -ge $MAX_RETRIES ]]; then
    echo -e "${RED}✗${NC} Failed after $attempt attempt(s) (exit code $exit_code)" >&2
    exit $exit_code
  fi

  if $BACKOFF; then
    wait=$(( 1 << attempt ))
    wait=$(( wait > BACKOFF_MAX ? BACKOFF_MAX : wait ))
  else
    wait=$DELAY
  fi

  echo >&2
  echo -e "${RED}✗${NC} Attempt $attempt failed (exit code $exit_code) — retrying in ${wait}s..." >&2
  echo >&2
  sleep "$wait"
done

Example usage:

# Retry indefinitely with 1s delay between attempts
retry git push

# Limit to 5 attempts
retry --retries 5 git push

# Exponential backoff — delays double each attempt (1s, 2s, 4s...)
retry --backoff git fetch

# 10 attempts with backoff, capped at 60s between retries
retry --retries 10 --backoff --max-delay 60 git fetch