What in the world am I missing?

The error is in your problem definition. Your regexp does exactly what you said you wanted it to do. It's searching for a string optionally surrounded by '{' and '}'. {hello is optionally surrounded by {...} since it's is not surrounded by {...}. 

'oh {hello there' =~ /
   ([{]{0,1})  # Matches '' (after some backtracking)
   hello       # Matches 'hello'
   (?(1)\})    # Matches ''
/x;

[download]
'oh hello} there' =~ /
   ([{]{0,1})  # Matches ''
   hello       # Matches 'hello'
   (?(1)\})    # Matches ''
/x;

[download]

As you can see, searching for a string optionally surrounded by something is the same thing as searching for the string itself.

From your expected results, I deduce you actually want a string that is surrounded by {...}, or one that is neither preceded by { nor followed by }. 

/
   {hello}   # '{hello}'
|
   (?<! { )  # Not preceded by '{'
   hello     # 'hello'
   (?! } )   # Not followed by '}'
/x

[download]

In reply to Re: Regex conditional match if previous match in same expression is true? by ikegami
in thread Regex conditional match if previous match in same expression is true? by radiantmatrix

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