Optional auto-switching

README.md

@@ -12,6 +12,7 @@ Changes your `$GEM_HOME`.
   * Prepends the new `$GEM_HOME/bin` to `$PATH` so it takes precedence.
 * Compartmentalizes gems into `.gem/$ruby_engine/$ruby_version`.
 * Plays nicely with [RVM] and [chruby].
+* Optional auto-switching.
 * Supports [bash] and [zsh].
 * Small (~90 LOC).
 * Has tests.
@@ -100,6 +101,19 @@ fi
 This will prevent `gem_home` from accidentally being loaded by `/bin/sh`, which
 is not always the same as `/bin/bash`.
 
+### Auto-switching
+
+This feature's workflow is similar to [chruby's `auth.sh`](https://github.com/postmodern/chruby/blob/master/share/chruby/auto.sh):
+
+If you want to auto-switch current `$GEM_HOME` when you cd between your different projects, simply load `auto.sh` in `~/.bashrc` or `~/.zshrc`:
+
+``` bash
+source /usr/local/share/gem_home/gem_home.sh
+source /usr/local/share/gem_home/auto.sh
+```
+
+gem_home will check the current and parent directories for a `.ruby-gemhome` file, which contains a path to the custom $GEM_HOME.
+
 ## Uninstall
 
 After removing the `gem_home` configuration:

share/gem_home/auto.sh

@@ -0,0 +1,35 @@
+unset GEM_HOME_AUTO
+
+if [ -z "$GEM_HOME_FILENAME" ]; then
+  export GEM_HOME_FILENAME=".ruby-gemhome"
+fi
+
+function gem_home_auto() {
+	local dir="$PWD/" gem_dir
+
+	until [[ -z "$dir" ]]; do
+		dir="${dir%/*}"
+
+		if { read -e gem_dir <"$dir/$GEM_HOME_FILENAME"; } 2>/dev/null || [[ -n "$gem_dir" ]]; then
+			if [[ "$gem_dir" == "$GEM_HOME_AUTO" ]]; then return
+			else
+				GEM_HOME_AUTO="$gem_dir"
+				gem_home "$gem_dir"
+				return $?
+			fi
+		fi
+	done
+
+	if [[ -n "$GEM_HOME_AUTO" ]]; then
+		gem_home -
+		unset GEM_HOME_AUTO
+	fi
+}
+
+if [[ -n "$ZSH_VERSION" ]]; then
+	if [[ ! "$preexec_functions" == *chruby_auto* ]]; then
+		preexec_functions+=("gem_home_auto")
+	fi
+elif [[ -n "$BASH_VERSION" ]]; then
+	trap '[[ "$BASH_COMMAND" != "$PROMPT_COMMAND" ]] && gem_home_auto' DEBUG
+fi