then try this (with all the bells and whistles for shelling out user input):

use IPC::Cmd;
sub _userinput2filename {
  my $cmd = $_[0];
  print "executing >>unchecked<< user-input : '$cmd'\n";
  # see https://perldoc.perl.org/IPC/Cmd.html for more details:
  my( $success, $error_message, $full_buf, $stdout_buf, $stderr_buf ) 
+= 
     IPC::Cmd::run(    
        command => $cmd,
        verbose => 1,
     );
   die "failed : $error_message (@$stderr_buf)" unless $success;
   # this is the stdout of the command
   return $stdout_buf
}
[download]

userinput2filename($string) will run each `command` block in $string and substitute it with the result of command's execution (stdout with all newlines in there) unless there is a failure whereas it dies. Regards to over the hills and far away...

Edit: it needs the sub (userinput2filename) and main from my previous post.