scripts/update: add a --dry-run option

scripts/update

@@ -9,6 +9,7 @@ usage() {
   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"
+  exit 1
 }
 
 warn() {
@@ -18,6 +19,14 @@ info() {
   echo "$@"
 }
 
+hasEffect() {
+  if [ -n "$dryRun" ]; then
+    echo "dry-run: skip $@"
+  else
+    eval "$@"
+  fi
+}
+
 # usage: getPkgs outVar prefix
 getPkgs() {
   local -n attrsArr="$1"
@@ -27,7 +36,7 @@ getPkgs() {
   fi
 
   local attrs="$(nix-env -f . --query --available --attr-path --no-name -A $attrPrefix)"
-  attrsArr=($attrs)
+  attrsArr+=($attrs)
 }
 
 updateOnePkg() {
@@ -45,9 +54,35 @@ updateOnePkg() {
   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
 }
 
+dryRun=
+toplevelsToUpdate=()
+parseArgs() {
+  while [ "$#" -ne 0 ]; do
+    local arg=$1
+    shift
+    case "$arg" in
+      (--help)
+        usage
+        ;;
+      (--dry-run)
+        dryRun=1
+        ;;
+      (*)
+        toplevelsToUpdate+=("$arg")
+        ;;
+    esac
+  done
+  if [ "${#toplevelsToUpdate[@]}" -eq 0 ]; then
+    toplevelsToUpdate=(sane)
+  fi
+}
+
+parseArgs "$@"
 pkgsToUpdate=()
-getPkgs pkgsToUpdate
+for t in "${toplevelsToUpdate[@]}"; do
+  getPkgs pkgsToUpdate "$t"
+done
 
 for p in "${pkgsToUpdate[@]}"; do
-  updateOnePkg "$p"
+  hasEffect updateOnePkg "$p"
 done