The older ELinks versions (up to 0.4.3) send:

ELinks ($version; $osinfo; $textmode_dimensions)

The new ELinks versions (from 0.9.0 on) send:

ELinks/$version (textmode; $osinfo; $textmode_dimensions)

You should therefore check against something like /^ELinks[\/ ]/, since more fields can be added inside the parenthesis in subsequent versions. Note that users can change their User-Agent through the options system.