* Will use existing kerl from $PATH (like installed by Homebrew) or…

… fetch specific version when setting `ASDF_KERL_VERSION`.

* Will use git to clone `kerl` quitly and checkout versioned tags instead of downloading from Github CDN.

* Enable shell docs out of the box by default and allow opt out using KERL_BUILD_DOCS="no" - technically any value will opt out, kerl just checks if it's set, and not its value. Since we're opting in by default, we will check != "yes" for opt out.

* Will come with out of the box settings for `KERL_CONFIGURE_OPTIONS` with additional settings for macOS that matches `Homebrew`
	* --disable-debug
	* --disable-silent-rules
	* --enable-dynamic-ssl-lib
	* --enable-hipe
	* --enable-sctp
	* --enable-shared-zlib
	* --enable-smp-support
	* --enable-threads
	* --enable-wx
	* --without-javac
	* macOS only:
		* --with-ssl=$(brew --prefix openssl)
		* --enable-darwin-64bit
		* --enable-kernel-poll
		* --with-dynamic-trace=dtrace

* macOS only: Unless custom `KERL_CONFIGURE_OPTIONS`, asdf-erlang will default to using Homebrew for following dependencies:
	- autoconf
 	- libtool
 	- openssl
 	- wxmac

This will allow `asdf-erlang` & `asdf-elixir` to be used out of the box and be much easier for majority of macOS users.
Avoiding using esotoric configuration and environment variables to keep track for various plugins should be a focus.
Allowing someone to just put a plugin in, and pick a verison without sifting through massive documentation and configuration is beneficial.

bin/install

@@ -1,12 +1,71 @@
 #!/usr/bin/env bash
 
+export KERL_BUILD_DOCS="${KERL_BUILD_DOCS:-yes}"
+
 set -e
 
-# shellcheck source=../bin/utils.sh
-source "$(dirname "$0")/utils.sh"
+
+# shellcheck source=../lib/utils.sh
+source "$(dirname $0)/../lib/utils.sh"
 
 install_erlang() {
   ensure_kerl_setup
+
+
+  if [ -z "$KERL_CONFIGURE_OPTIONS" ]; then 
+    echo "KERL_CONFIGURE_OPTIONS is not set, will use default settings."
+
+    export KERL_CONFIGURE_OPTIONS="--disable-debug --disable-silent-rules --enable-dynamic-ssl-lib"
+    export KERL_CONFIGURE_OPTIONS="$KERL_CONFIGURE_OPTIONS --enable-hipe --enable-sctp --enable-shared-zlib --enable-smp-support"
+    export KERL_CONFIGURE_OPTIONS="$KERL_CONFIGURE_OPTIONS --enable-threads --enable-wx --without-javac"
+
+    if [ "$(uname -s)" = "Darwin" ]; then
+      echo "Using Homebrew for dependencies."
+      if [ -x "$(command -v brew)" ]; then
+        if [ ! -d "$(brew --prefix autoconf)" ]; then
+          echo "Missing autoconf from Homebrew"
+          echo "brew install autoconf"
+          exit 1
+        fi
+        if [ ! -d "$(brew --prefix libtool)" ]; then
+          echo "Missing libtool from Homebrew"
+          echo "brew install libtool"
+          exit 1
+        fi
+        if [ ! -d "$(brew --prefix openssl)" ]; then
+          echo "Missing openssl from Homebrew"
+          echo "brew install openssl"
+          exit 1
+        fi
+        if [ ! -d "$(brew --prefix wxmac)" ]; then
+          echo "Missing wxmac from Homebrew"
+          echo "brew install wxmac"
+          exit 1
+        fi
+        export KERL_CONFIGURE_OPTIONS="$KERL_CONFIGURE_OPTIONS --with-ssl=$(brew --prefix openssl) --enable-darwin-64bit --enable-kernel-poll --with-dynamic-trace=dtrace"  
+      else
+        echo "Homebrew is not installed or in PATH"
+        echo "To install without Homebrew, set your own KERL_CONFIGURE_OPTIONS"
+      fi
+    fi
+  fi
+
+
+
+
+
+
+  echo "Installing Erlang $ASDF_INSTALL_VERSION"
+  if [ "$KERL_BUILD_DOCS" != "yes" ]; then
+    unset KERL_BUILD_DOCS
+    echo "without documentation"
+  else
+    echo "With documentation"
+  fi
+  echo "With KERL_CONFIGURE_OPTIONS set to: "
+  echo "$KERL_CONFIGURE_OPTIONS"
+  echo "---"
+
   local asdf_activation_version
   local build_name
 
@@ -17,6 +76,7 @@ install_erlang() {
   $(kerl_path) delete installation "$build_name" || true
   $(kerl_path) delete build "$build_name" || true
 
+
   if [ "$ASDF_INSTALL_TYPE" = "ref" ]; then
     asdf_activation_version="$ASDF_INSTALL_TYPE:$ASDF_INSTALL_VERSION"
     $(kerl_path) build git "${OTP_GITHUB_URL:-https://github.com/erlang/otp.git}" "$ASDF_INSTALL_VERSION" "$build_name"

bin/list-all

@@ -1,10 +1,11 @@
 #!/usr/bin/env bash
 
-source "$(dirname $0)/utils.sh"
+# shellcheck source=../lib/utils.sh
+source "$(dirname $0)/../lib/utils.sh"
+
 
 list_all() {
     ensure_kerl_setup
-
     echo "$("$(kerl_path)" list releases | sed -e 's:Run.*::' | tr '\n' ' ')"
 }
 

bin/uninstall

@@ -2,7 +2,8 @@
 
 set -e
 
-source "$(dirname $0)/utils.sh"
+# shellcheck source=../lib/utils.sh
+source "$(dirname $0)/../lib/utils.sh"
 
 ensure_kerl_setup
 

lib/utils.sh

@@ -0,0 +1,74 @@
+KERL_VERSION="${ASDF_KERL_VERSION:-2.1.0}"
+
+
+echoerr() {
+  >&2 echo -e "\033[0;31m$1\033[0m"
+}
+
+ensure_kerl_setup() {
+  export KERL_BASE_DIR="$(kerl_dir)"
+  export KERL_CONFIG="$(kerl_dir)/kerlrc"
+  #export KERL_BUILD_BACKEND="git"
+  ensure_kerl_installed
+}
+
+ensure_kerl_installed() {
+  # If kerl exists
+  if [ -x "$(kerl_path)" ]; then
+    # But was passed an expected version
+    if [ -n "${ASDF_KERL_VERSION:-}" ]; then
+      current_kerl_version="$("$(kerl_path)" version)"
+      # Check if expected version matches current version
+      if [ "$current_kerl_version" != "$KERL_VERSION" ]; then
+        # If not, reinstall with ASDF_KERL_VERSION
+        download_kerl
+      fi
+    fi
+  else
+    # kerl does not exist, so install using default value in KERL_VERSION
+    download_kerl
+  fi
+}
+
+
+
+download_kerl() {
+  # Remove directory in case it still exists from last download
+  rm -rf "$(kerl_source_dir)"
+  rm -rf "$(kerl_dir)"
+
+  # Print to stderr so asdf doesn't assume this string is a list of versions
+  echoerr "Downloading kerl $KERL_INSTALL_VERSION"
+
+  # Clone down and checkout the correct kerl version
+  git clone https://github.com/kerl/kerl.git "$(kerl_source_dir)" --quiet
+  (cd "$(kerl_source_dir)"; git checkout $KERL_INSTALL_VERSION --quiet;)
+
+  mkdir -p "$(kerl_dir)/bin"
+  mv "$(kerl_source_dir)/kerl" "$(kerl_path)"
+  chmod +x "$(kerl_path)"
+
+  rm -rf "$(kerl_source_dir)"
+}
+
+asdf_erlang_plugin_path() {
+  echo "$(dirname "$(dirname "$0")")"
+}
+
+kerl_dir() {
+  echo "$(asdf_erlang_plugin_path)/kerl"
+}
+
+kerl_source_dir() {
+  echo "$(asdf_erlang_plugin_path)/kerl-install-source"
+}
+
+
+kerl_path() {
+  #Check if kerl exists without an expected version
+  if [ -x "$(command -v kerl)" ] && [ -z "${ASDF_KERL_VERSION:-}" ]; then
+    echo "$(command -v kerl)"
+  else
+    echo "$(kerl_dir)/bin/kerl"
+  fi
+}