Rails custom route with constraints - regexp anchor characters are not allowed in routing requirements

The regex anchors are ^ and $, but they don't achieve anything here. "(Y)ou don’t need to use anchors because all routes are anchored at the start.".

So the constraint:

:constraints => { :name => /[a-zA-Z0-9_]+/ }

will do what you want - ensure the name is composed of 1 or more of those characters, and nothing else. BTW you can simplify the regex:

:constraints => { :name => /\w+/ }

In regex we have two anchors:

1. Beginning of line/string ^
2. End of line/string $

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Try to remove $ from the pattern and you should be good to go...