Retry a command with exponential backoff

Thu, 14 May 2026 00:00:00 +0000

Network calls fail for a second and then work fine. A script shouldn’t die over that. This wraps any command, retrying with a doubling delay.

# retry — run a command up to N times with exponential backoff.
# Usage: retry 5 curl -sf https://example.com
retry() {
 local max="$1"; shift
 local n=1 delay=1
 until "$@"; do
 if (( n >= max )); then
 echo "retry: '$*' failed after $max attempts" >&2
 return 1
 fi
 echo "retry: attempt $n failed; sleeping ${delay}s" >&2
 sleep "$delay"
 (( n++, delay *= 2 ))
 done
}

It returns the command’s success once it passes, or 1 after exhausting the attempts — so it drops straight into a set -e script:

Auto-load a Nix flake dev shell with direnv

Sat, 09 May 2026 00:00:00 +0000

A project’s tools should appear when you enter its directory and vanish when you leave. direnv + nix-direnv does exactly that — this .envrc loads a named flake dev shell on cd.

# .envrc — auto-load a named Nix flake dev shell.
# Needs direnv + nix-direnv: https://github.com/nix-community/nix-direnv

if ! has nix_direnv_version || ! nix_direnv_version 3.0.0; then
 source_url "https://raw.githubusercontent.com/nix-community/nix-direnv/3.0.0/direnvrc" \
 "sha256-21TMnI2xWX7HkSTjFFri2UaohXVj854mgvWapWrxRXg="
fi

# Loads devShells.<system>.myshell — drop the suffix for the default shell.
use flake .#myshell

# Untracked local overrides, if any.
[ -f .envrc.local ] && source_env .envrc.local

Run direnv allow once; after that the shell rebuilds itself whenever flake.nix changes.

Shell on buildx.sh

Retry a command with exponential backoff

Auto-load a Nix flake dev shell with direnv