enhance nvm-exec

add -v option; try to use realpath to find nvm's dir; support exec nvm itself

nvm-exec

@@ -1,15 +1,85 @@
 #!/usr/bin/env bash
 
-DIR="$(command cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )"
+#
+# Regular commands can be executed as
+#
+#     sudo nvm-exec [-v 6.9.2] npm install -g npm
+#
+# If no -v option provided, then try to use $NODE_VERSION, .nvmrc, default, and finally current
+#
+# When using sudo, use "sudo -E" to preserve env to pass NODE_VERSION.
+#
+# nvm commands can be executed as
+#
+#     sudo nvm-exec nvm install 6.9.2
+#     sudo nvm-exec nvm alias default 6.9.2
+#
+
+function nvm_fail() {
+  echo "$1" >&2
+  exit 127
+}
+
+has_realpath=""
+
+function find_nvm_dir() {
+  if which realpath >& /dev/null; then
+    has_realpath=yes
+    dirname "$(realpath "$0")"
+  else
+    command cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd
+  fi
+}
+
+DIR="$(find_nvm_dir)"
+
+function check_nvm_sh() {
+  if [ ! -f "$DIR/nvm.sh" ]; then
+    local rp_msg=""
+    [ "$has_realpath" == "yes" ] || rp_msg="; missing realpath command for finding nvm-exec's realpath to search for nvm.sh"
+    nvm_fail "Unable to find nvm.sh at $DIR$rp_msg"
+  fi
+}
+
+check_nvm_sh
+
+function nvm_use() {
+  nvm use "$1" > /dev/null || nvm_fail "nvm use $2 failed"
+}
+
+function nvm_use_v() {
+  [ -n "$1" ] && nvm_use "$1" "$2"
+}
+
+opt_version=""
+
+if [ "$1" == "-v" ]; then
+  shift
+  opt_version=$1
+  shift
+fi
+
+function check_version() {
+  nvm_use_v "$opt_version" "(-v $opt_version)" && return
+  nvm_use_v "$NODE_VERSION" "(NODE_VERSION $NODE_VERSION)" && return
+
+  local nvmrc
+  nvmrc=$(nvm which 2>&1 | grep ^Found | grep -o "\'.*\.nvmrc\'")
+  [ -n "$nvmrc" ] && nvm_use "" "with $nvmrc file" && return
+
+  nvm which default >& /dev/null && nvm_use_v default default && return
+  nvm which current >& /dev/null && nvm_use_v current current && return
+
+  nvm_fail "No -v option or NODE_VERSION provided; no .nvmrc file, no default, and no current found"
+}
 
 # shellcheck disable=SC1090
 \. "$DIR/nvm.sh" --no-use
 
-if [ -n "$NODE_VERSION" ]; then
-  nvm use "$NODE_VERSION" > /dev/null || exit 127
-elif ! nvm use >/dev/null 2>&1; then
-  echo "No NODE_VERSION provided; no .nvmrc file found" >&2
-  exit 127
+if [ "$1" == "nvm" ]; then
+  eval "$@"
+else
+  check_version
+  exec "$@"
 fi
 
-exec "$@"