Rubymine shortcut to insert

The default shortcut is Ctrl+Shift+Period on Windows and Cmd+Shift+Period on Mac. It may not work on all the keyboards, in which case you can change it in Settings (Preferences on Mac) | Keymap: Main Menu, Tools, Erb, Insert <%= %>:

You can also use code completion:

After accepting this choice you’ll get:

<%= | %>

Another option is to define a live template:

Type re, then Tab to expand.

Finally, you can define a keyboard shortcut for any text/template using the following trick:

1. Edit | Macros | Start Macro Recording
2. Type re, then Tab
3. Edit | Macros | Stop Macro Recording
4. Save it under RubyExpression name

Now go to Keymap settings and assign a shortcut to RubyExpression under Edit, Macros.