As always, There Is More Than One Way To Do It. If you're certain that the grep condition will always match exactly one element of @files:

• $ScontrolFile = (grep {/_CF_/} @files)[0]; - create a "temporary" list and get its first element
• ($ScontrolFile) = grep {/_CF_/} @files; - use assignment in list context
• use List::Util qw/first/; $ScontrolFile = first {/_CF_/} @files; - use first from the core module List::Util, which has the advantage that it stops looking once it finds a match

However, none of the above solutions provide protection against the case that @files does not contain exactly one string matching the pattern, which is why I suggested the extra array. <update> AnomalousMonk showed a way to add the check to the second of my examples above. To add a check to the other two, </update> you could theoretically search the array a second time, using grep in scalar context (if ( grep({/_CF_/} @files)!=1 ) { die ... }), but that's fairly wasteful and you'll have duplicated code (the grep block). Of course, you can also write an explicit loop:

my $ScontrolFile;
for my $file (@files) {
    if ( $file =~ /_CF_/ ) {
        die "more than one _CF_ file found in: @files"
            if defined $ScontrolFile;
        $ScontrolFile = $file;
    }
}
die "_CF_ file not found in: @files" unless defined $ScontrolFile;
[download]

Update: Added check for >1 file in the above code, and see update in text.

@files = grep { /_CF_/ } @files;
[download]

But it is probably clearer (and easier to debug if you need) to grep the matching values into a new array and leave the original one untouched.

Yet Another Way to capture first matching file, if any, and number of matching files concisely:

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
[download]

Update: Be aware that if no files match the grep condition in the example code above,  $first_CF_ is undefined.