how to create a regex that doesn't contain a text but starts with a specified text?

Question

Hi I'd like to create a regex that check if my string starts with a / but no matter where shouldn't contains /! so:
/xxxx = true
/xxxx/yyyy = true
/!xxxx = false
/xxxx/!yyyy = false
xxxx = false
I tried this but it doesn't seems to work:
^/(?!(/!)(.*|/!.*))*$

The fourth bird · Answer

As /!xxxx should also be false, the lookahead should be at the start of the string or else you will miss checking the leading /.
To find /! anywhere in the string, you could prepend  .*
^(?!.*/!)/.*

Regex demo

how to create a regex that doesn't contain a text but starts with a specified text?

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