upd

UPD

Upgrade NPM Package Dependencies — fast, safe, formatting-preserving.

A Go CLI that bumps dependency versions in an NPM package.json while byte-preserving all original JSON formatting — whitespace, key order, and quoting style stay exactly as you wrote them. Only the version number inside each constraint string changes. Nothing else is touched.

Go rewrite of rse/upd — the original JavaScript/Node.js CLI by Dr. Ralf S. Engelschall.

Demo

Features

• Formatting-preserving edits — surgically replaces only the version bytes inside each constraint string. Your indentation, key order, and quoting style are never touched.
• TOCTOU-safe atomic writes — stages a temp file, fsyncs it, verifies the on-disk fingerprint hasn't changed since read, then atomically renames. If another process (npm install, IDE formatter) edited package.json during the network-fetch window, the write is aborted and your file is left untouched.
• Concurrent registry queries — fetches packuments in parallel with a configurable connection pool (default 8).
• Semantic version resolution — resolves to dist-tags.latest by default, or the highest semver across all published versions with -g.
• Pin latest tags — -P / --pin-latest rewrites bare "latest" tags to their exact resolved semver (e.g. "latest" → "7.7.4").
• Glob pattern filtering — update only matching dependencies, with !-prefixed exclusions (e.g. upd react* !react-dom).
• All four dependency sections — dependencies, devDependencies, peerDependencies, optionalDependencies.
• Character-level diff highlighting — shows exactly which characters changed in red/green.
• Embedded defaults — an "upd" field in package.json supplies default CLI arguments so you don't repeat yourself.
• Single static binary — no runtime dependencies, no Node.js required.

Quick Start

# Install (requires Go 1.26+ with GOEXPERIMENT=jsonv2)
GOEXPERIMENT=jsonv2 go install github.com/LarsArtmann/upd/cmd/upd@latest

# Dry run — show what would change without writing
upd -n

# Apply updates
upd

Why GOEXPERIMENT=jsonv2? upd uses Go's encoding/json/v2 for byte-precise JSON editing. This flag will become unnecessary once the Go team stabilizes the json/v2 package in a future release.

Example output (upd -n -C):

┌─────────────────────────────────────┬──────────────┬──────────────┬─────────┐
│MODULE NAME                          │VERSION OLD   │VERSION NEW   │STATE    │
├─────────────────────────────────────┼──────────────┼──────────────┼─────────┤
│express                              │^4.18.0       │^5.2.1        │updated  │
│jest                                 │^29.5.0       │^30.4.2       │updated  │
│lodash                               │^4.17.20      │^4.18.1       │updated  │
│typescript                           │^5.2.0        │^7.0.2        │updated  │
└─────────────────────────────────────┴──────────────┴──────────────┴─────────┘

Installation

Go

GOEXPERIMENT=jsonv2 go install github.com/LarsArtmann/upd/cmd/upd@latest

Requires Go 1.26+ with the json/v2 experiment enabled.

Nix

# Run directly without installing
nix run github:LarsArtmann/upd

# Install to your profile
nix profile install github:LarsArtmann/upd

Build from source

git clone https://github.com/LarsArtmann/upd.git
cd upd
nix run .#build    # or: GOEXPERIMENT=jsonv2 go build -o upd ./cmd/upd

Usage

upd [-h] [-V] [-q] [-n|--dry-run] [-C] [-f <file>] [-r <registry>] [-g] [-a] [-c <concurrency>] [-P] [-t <timeout>] [--retries <n>] [--json] [--verbose] [<pattern> ...]

Color auto-detection: Colors are automatically disabled when the NO_COLOR environment variable is set (see no-color.org) or when stdout is not a terminal (piped/redirected). Use -C to force-disable.

Examples:

upd                          # update all dependencies
upd -n                       # dry run (preview changes)
upd react*                   # only update packages matching "react*"
upd react* !react-dom        # update react packages except react-dom
upd -g                       # use greatest version (include pre-releases)
upd -P                       # pin "latest" tags to exact versions
upd -c 16 lodash*            # 16 concurrent connections, only lodash
upd -f alt.json -n           # preview changes to alt.json

How It Works

Byte-preserving edits

upd parses package.json with a streaming JSON decoder that tracks byte offsets. When a version needs updating, it splices only the version bytes out of the raw file and inserts the new ones. The rest of the file — every space, newline, key ordering, and quoting choice — is preserved exactly. No re-serialization, no formatter arguments, no diffs to resolve.

Version resolution

Each dependency constraint is classified by a regex:

• Upgradable — strings starting with a digit, optionally preceded by ^ or ~ (e.g. 1.2.3, ^1.2.3, ~2.3.4, 1.x). The prefix is preserved on update: ^1.2.3 → ^2.0.0.
• Skipped — comparator ranges (>=1.0.0), tags (latest), git/file URLs — anything containing <>|=. Use -P to opt-in to pinning latest.
• Ignored — names that don't match any supplied glob pattern.

After resolving the target version from the NPM registry, a semver comparison guards against downgrades: if the resolved version isn't actually newer, the dependency is marked kept.

Atomic writes with TOCTOU protection

The write path uses go-atomic-write to prevent data loss when another process edits package.json during the network-fetch window. It stages a temp file, fsyncs it, acquires a cross-platform file lock, verifies the on-disk fingerprint hasn't changed since read, then atomically renames. On mismatch it aborts with ErrConcurrentModification — the file is untouched.

See docs/atomic-writes.md for the full step-by-step breakdown and flow diagram.

Configuration

Embedded upd field

Add an "upd" field to your package.json to supply default arguments that are prepended to CLI flags:

{
  "upd": ["react*", "!react-dom", "-c", "16"],
  "dependencies": {
    "react": "^18.0.0",
    "react-dom": "^18.0.0",
    "lodash": "^4.17.20"
  }
}

Now upd is equivalent to upd react* !react-dom -c 16. CLI flags override or supplement these defaults. The field accepts a string or an array.

Exit Codes

In CI, check for exit 75 to decide whether to retry the job. Exit 1 means something needs human attention (typo in dependency name, malformed JSON, etc.).

Troubleshooting

ERROR: package not found in NPM registry (exit 1) The package name in package.json doesn't exist on the registry. Check for typos, check if the package was unpublished, or verify you're using the correct registry (-r/--registry).

ERROR: NPM registry is unavailable (exit 75) The registry returned a server error (5xx) or timed out. This is transient — re-run upd after a few seconds. If using a private registry, verify it's running and accessible. Use --retries to increase the number of retry attempts.

ERROR: package configuration file was modified concurrently Another process (npm install, IDE auto-save, formatter) edited package.json while upd was fetching versions. Your file was not changed. Simply re-run upd.

ERROR: invalid JSON in package configuration file Your package.json has malformed JSON. Run npx jsonlint package.json or node -e "JSON.parse(require('fs').readFileSync('package.json','utf8'))" to find the syntax error.

Progress bar is garbled or leaves artifacts The progress bar is cleared using a fixed-width reset. If your terminal is narrower than 80 characters, use -q (quiet mode) to suppress it.

Colors appear in piped output Colors are auto-disabled when stdout is not a terminal or NO_COLOR is set. If you still see colors, ensure no tool in your pipeline (e.g. script) is emulating a TTY. You can always force-disable with -C.

Development

This repo uses Nix flakes for all build automation:

nix run .#build          # build to bin/upd
nix run .#test           # go test ./... -v -count=1
nix run .#lint           # go vet + go build + golangci-lint
nix run .#run -- <args>  # go run ./cmd/upd <args>
nix flake check          # validate the flake

Plain Go equivalents (requires GOEXPERIMENT=jsonv2):

export GOEXPERIMENT=jsonv2   # required — uses encoding/json/v2
go build ./cmd/upd
go test -race ./...
go vet ./...

Render the demo

nix run .#demo              # render GIF locally to demo/
nix run .#demo -- --publish # render + upload to vhs.charm.sh cloud

Origin

• Original: rse/upd — an npm package written in JavaScript/Node.js by Dr. Ralf S. Engelschall.
• This project: a complete Go rewrite by Lars Artmann, keeping the same CLI behavior and philosophy while leveraging Go's performance, compile-time type safety, and single-binary distribution.

License

MIT — Copyright © 2015-2026 Dr. Ralf S. Engelschall, Copyright © 2026 Lars Artmann.

See LICENSE for the full text.