It seems that what you are looking for is the "s" modifier for regex. Try: 
 $_ =~ s/[\s\r\n\t]//sg;

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Also note - since the \s \r .. etc are alternative characters, and NOT a sequence, I have placed them in [brackets].

From the docs:

s     Treat string as single line. That is, change "." to match any character whatsoever, even a newline, which normally it would not match.
Update: Ignore the suggestion to use the "s" modifier. It is not necessary. See jwkrahn note below.

             I hope life isn't a big joke, because I don't get it.
                   -SNL

In reply to Re^3: concatenating multiple lines without using . operator by NetWallah
in thread concatenating multiple lines without using . operator by anonym

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