find (\&process, $folder);

sub process {
    if ($_ =~ /\.9$/) {    
        print "\nProcessing file $File::Find::dir/$_\n";
        open FILE, $_ or die "Cannot read $File::Find::name: $!";
        local $/= "# input for";  
        
        # localise @outlines so we don't accumulate
        my @outlines = ();  
    
        while ( my $line = <FILE> ) {        
            #do something        
            push @outLines, $line;
        }
        close FILE;
    
        my $out = 'adjusted.learn';
        open OUTFILE, ">$out" or die "Cannot write $out: $!";
        print OUTFILE @outLines;
        close OUTFILE;    
    }
}

exit;