[... some stuff here ] 

if ( $var eq "*" ) {
   $file = "name*"; # is some real file with an Asterix to search only on them in the real code
   my $ls = $sftp->ls (wanted => qr/$file}/ )  or die "unable to retrieve directory: ".$sftp->error; 
   print "$_->{longname}\n" for (@$ls);

} else { 
   $file = "realname.ext"; # existing file 
   say $file;
   # reading - default method - from the remote file
   $fh1 = $sftp->open("$file") or die $sftp->error;
   while (<$fh1>) {
     print if  /ORA-/ || /Fehler/ || /ORACLE-Fehler/; 
     # my $last = $_;
     # print $last;
   }
exit 0;