How to add custom hyperlink field merged with another custom field

[Deleted user]

I am trying to do the following but have no idea how to go about it.

# I have a custom field (CustomFieldId_12345) with a value AAA12345

# And I want to create a new custom field (CustomFieldId_12346) that will work as a hyperlink and will be auto-populated when the issue is created and the field above is not blank. The output of this field will be something along the lines 

https://example.com/ + value of CustomFieldId_12345 therefore the end result is https://example.com/AAA12345 but the display name of this link is "Example"

I tried creating a blank text field and use a post function to update it with the above but have no idea how to join the hyperlink with the custom field value, to make the new hyperlink and then just show the display name

Any help would be much appreciated.