scripts: add an "update" script to update all my packages

it probably doesnt update feeds yet, though

scripts/update

@@ -0,0 +1,53 @@
+#!/usr/bin/env nix-shell
+#!nix-shell -i bash -p nix-update
+
+usage() {
+  echo "update: update rev/hash for one or more packages"
+  echo "usage: update [attr-path]"
+  echo ""
+  echo "examples:"
+  echo "update nixpkgs: update only the nixpkgs input"
+  echo "update sane: update every package under the 'sane' attribute"
+  echo "update: update everything i know how to update"
+}
+
+warn() {
+  echo "$@"
+}
+info() {
+  echo "$@"
+}
+
+# usage: getPkgs outVar prefix
+getPkgs() {
+  local -n attrsArr="$1"
+  local attrPrefix="$2"
+  if [ -z "$attrPrefix" ]; then
+    attrPrefix=sane
+  fi
+
+  local attrs="$(nix-env -f . --query --available --attr-path --no-name -A $attrPrefix)"
+  attrsArr=($attrs)
+}
+
+updateOnePkg() {
+  local attrPath="$1"
+  local updateScript="$(nix eval --raw -f . $attrPath.passthru.updateScript --apply 'builtins.concatStringsSep "'" "'"')"
+  if [ -z "$updateScript" ]; then
+    warn "don't know how to update '$attrPath'"
+    return
+  fi
+  local UPDATE_NIX_NAME="$(nix eval --raw -f . $attrPath.name)"
+  local UPDATE_NIX_PNAME="$(nix eval --raw -f . $attrPath.pname)"
+  local UPDATE_NIX_OLD_VERSION="$(nix eval --raw -f . $attrPath.version)"
+  info "updating: '$attrPath'"
+  # we lose spaces inside the exec args... could `nix eval` without `--raw` to fix that.
+  UPDATE_NIX_NAME="$UPDATE_NIX_NAME" UPDATE_NIX_PNAME="$UPDATE_NIX_PNAME" UPDATE_NIX_OLD_VERSION="$UPDATE_NIX_OLD_VERSION" UPDATE_NIX_ATTR_PATH="$attrPath" eval $updateScript
+}
+
+pkgsToUpdate=()
+getPkgs pkgsToUpdate
+
+for p in "${pkgsToUpdate[@]}"; do
+  updateOnePkg "$p"
+done