Clunky, but clear, change that line in the array and re-write the file: 
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 );

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In reply to Re^3: searching for a substring in a string by punch_card_don
in thread searching for a substring in a string by Anonymous Monk

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