If I understand correctly, you want to do something like this:

/^abc$\ndef$/
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But you are faced with $\ getting treated as a variable name. You could use one of the following instead:

/^abc(?:$)\ndef$/m
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/^abc$(?:\n)def$/m
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/ ^ abc $ \n def $ /xm
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But the following ones are better:

/^abc\ndef$/m
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/ ^ abc \n def $ /xm
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