Left Function in Template

I don’t think there is. I’ve looked for this as well and could not find anything functions other than the # truthy or ^ falsy.

Can do this in a template field, but you can do this as a custom renderer in Javascript.  Here is a social security masking snippett.  You can probably repurpose.  
The field where you will show this data should use renderer type “custom”   The name should be the same as that you give the snippet. 
The snippet should be of type “In-Line Snippet” 

Here is the code: 

// Only use the last four digits of a string  (Like a SSN)
var field = arguments[0];
var value = arguments[1];
var minValue = value.substr(value.length - 4);
var text = “*--”+minValue;
skuid.ui.fieldRenderers.TEXT[field.mode](field, text);