while (<$FH>) modifies global variable $_. Whenever you modify a global variable, localize it! 
sub suck_this {
  my ($what) = @_ ;

  open my $FH, '<', \$what ;

  print " Read:" ;
  local $_;
  while (<$FH>) {
    s/\r/\\r/g ;
    s/\n/\\n/g ;
    print " '$_'" ;
  } ;

  print "\n" ;
} ;

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In reply to Re: Just when you thought you'd got it: 'foreach $f (@foo)' vs 'foreach (@foo)' by ikegami
in thread Just when you thought you'd got it: 'foreach $f (@foo)' vs 'foreach (@foo)' by gone2015

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