nixpkgs/pkgs/development/web/iojs/update-iojs

#!/bin/sh
#
# Fetch the latest io.js release (stable/nightly) and update
# `default.nix` in this directory.
#
# Call this from the root of your nixpkgs directory.
#

set -e

HERE="$(dirname "$0")"

latest() {
    curl -s "$1" | grep 'href="v' \
        | tail -1 | sed 's/.*href="v//;s/\/".*//'
}

latest_log() {
    echo "Getting latest $1 version from $2" >&2
    version=$(latest "$2")
    echo "version -> $version" >&2
    echo "$version"
}

url() {
    nix-instantiate -A "$1" \
        | xargs cat \
        | sed 's/.*"urls","//;s/".*//'
}

hash() {
    nix-prefetch-url "$1"
}

hash_log() {
    echo "Finding hash for $1" >&2
    value=$(hash "$1")
    echo "hash -> $value" >&2
    echo "$value"
}

stableVersion=$(latest_log stable 'https://iojs.org/dist/')
stableHash=$(hash_log "$(url iojs.src)")

sed -i \
    "/version = /s/\"[^\"]*\"/\"$stableVersion\"/" \
    "$HERE/default.nix"
sed -i \
    "/sha256 = /s/\"[^\"]*\"/\"$stableHash\"/" \
    "$HERE/default.nix"