Update: Ok the question was cleared up while I was writing this. Disreagard this post, the previous answers take care of it.

First, you want to be using s/// for regexes, not tr///.

$row_to_process =~ s/\s//g;

# If you wanted to use tr/// (probably a bit faster here)
$row_to_process =~ tr/ \n\t\r//d;
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Will remove all whitespace from a string. After this, your question is a little confusing. You talk about removing only single spaces. Why would the space between "It" and "is" and the space "cold" and "now" not be removed.