If you want to call a function inside of a string you need to either use a weird syntax or break up the string and concatenate,

 perl -e 'sub foo{return qq|xoxoxox|}; print qq|happy @{[&foo]} !|;'
happy xoxoxox !

# or

 perl -e 'sub foo{return qq|xoxoxox|}; print qq|happy |. &foo . q~!~;'
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