open ( FH, "p.txt" );
my @output = <FH>;
close ( FH );
open ( FH, ">p.txt" );
for $i (0 ..#@output) {
   if ($output[$i] =~ /.*(test.*\.txt).*/) {
      $output[$i] =~ s/.*(test.*\.txt).*/test29-01-05\.txt/
      last;
}
for $i (0 ..#@output) {
   print "$output[$i]";
}
close ( FH );