\b
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is equivalent to

(?:(?<=\w)(?!\w)|(?<!\w)(?=\w))
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If you want to include "-" as a word character, just change \w to [\w-].

(?:(?<=[\w-])(?![\w-])|(?<![\w-])(?=[\w-]))
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All together, that gives

my $my_slash_b = qr/(?:(?<=[\w-])(?![\w-])|(?<![\w-])(?=[\w-]))/;

/$my_slash_b$check$my_slash_b/
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But since you "know" that $check starts and ends with a word character, the above simplifies to

/(?<![\w-])$check(?![\w-])/
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If you wanted to go further and count any non-whitepspace as word characters, you're left with

my $my_slash_b = qr/(?:(?<=\S)(?!\S)|(?<!\S)(?=\S))/;

/$my_slash_b$check$my_slash_b/
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and thus

/(?<!\S)$check(?!\S)/
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