Remove all whitespace from file
perl -lape 's/\s+//sg' INPUT.TXT > OUTPUT.TXT
Remove whitespace more than one space
perl -wlpe '~ s/ +/ /g' INPUT.TXT > OUTPUT.TXT
Remove whitespace more than one space and replace with ‘_’ character
perl -wlpe '~ s/ +/_/g' INPUT.TXT > OUTPUT.TXT
