Basic approach is to read through the while file, and set the flag once you hit your marker, and print if the flag is set.

perl -ne 'if($ok){print;}else{$ok=/^This is the temp line\.$/}' foo.tx
+t
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Another approach, if the file is small enough, is to slurp into memory and split it, using your marker as the delimiter:

perl -n0777e 'print ((split(/^This is the temp line.\n/m, $_, 2))[-1])
+' foo.txt
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