c:\@Work\Perl\monks>perl -wMstrict -le
"my @files = qw(xxx  1st_CF_xx  CF__  2nd_CF_yy  CF);
 ;;
 my $n_CF_ = my ($first_CF_) = grep /_CF_/, @files;
 ;;
 print qq{number of _CF_ files: $n_CF_};
 if ($n_CF_ == 1) { print qq{just one: '$first_CF_'}; }
"
number of _CF_ files: 2

c:\@Work\Perl\monks>perl -wMstrict -le
"my @files = qw(xxx  1st_CF_xx  CF__  CF);
 ;;
 my $n_CF_ = my ($first_CF_) = grep /_CF_/, @files;
 ;;
 print qq{number of _CF_ files: $n_CF_};
 if ($n_CF_ == 1) { print qq{just one: '$first_CF_'}; }
"
number of _CF_ files: 1
just one: '1st_CF_xx'

c:\@Work\Perl\monks>perl -wMstrict -le
"my @files = qw(xxx  yyy  zzz);
 ;;
 my $n_CF_ = my ($first_CF_) = grep /_CF_/, @files;
 ;;
 print qq{number of _CF_ files: $n_CF_};
 if ($n_CF_ == 1) { print qq{just one: '$first_CF_'}; }
"
number of _CF_ files: 0