$hash{"$x,$y,$z"}{no} = $no;
$hash{"$x,$y,$z"}{pressure} = $pressure;
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Then with the coords from the second file, search in the hash for matching coords.

Problem: The coords have a lot of decimal places. These should be normalized before creating the hash entries, and before searching the hash keys. Decide how many significant digits are more than enough, and use sprintf with a fixed decimal ("f") descriptor.