new-style documentation for most commands

libexec/rbenv-exec

@@ -1,4 +1,18 @@
 #!/usr/bin/env bash
+#
+# Summary: Run an executable with the right Ruby version
+#
+# Usage: rbenv exec COMMAND [arg1 arg2...]
+#
+# Runs an executable by first preparing PATH so that the selected Ruby version
+# is prepended to it.
+#
+# For example, doing:
+#   RBENV_VERSION=1.9.3-p327 rbenv exec bundle install
+#
+# has an effect is if this was done:
+#   PATH=~/.rbenv/versions/1.9.3-p327:"$PATH" bundle install
+
 set -e
 [ -n "$RBENV_DEBUG" ] && set -x
 
@@ -11,7 +25,7 @@ export RBENV_VERSION="$(rbenv-version-name)"
 RBENV_COMMAND="$1"
 
 if [ -z "$RBENV_COMMAND" ]; then
-  echo "usage: rbenv exec COMMAND [arg1 arg2...]" >&2
+  rbenv-help --usage exec >&2
   exit 1
 fi