How can I get a field's value from a global based on a url segment? I have a rich text field with a handle of myTextField that I have included in a global set called firstGlobalSet.

What If I created another global set called secondGlobalSet and included the same field myTextField. 

How could I get the correct field from the correct global set based on url segment?

For example, mysite.com/first or mysite.com/second
You will need to access a few things. 


The url segment you need (for example the last segment)
The global set name
The field handle name


You can use getLastSegment to access the last url segment.

Using the global set names above let's say I have a url like this:

mysite.com/first

{% set segment = craft.request.getLastSegment() %}  // first


I know I've got a global set called firstGlobalSet, and now I've got first. We just need to put them together. You can use Craft's 
getSetByHandle method to access the global set via its handle.

{% set global = craft.globals.getSetByHandle(segment ~ 'GlobalSet') %}
{{ global }} // firstGlobalSet


Now that we've got the correct global set, we can get to the field we need. In this case it's myTextField.

{{ global.myTextField }}