my $url3="http://microrna.sanger.ac.uk/blah/blah";
my $content=get $url3;
[download]

I only used the special perl <DATA> file handle for the purposes of the example (so I could easily get a string of HTML). You won't need to do this as that is what LWP::Simple's get gives you.

You need to use the regex on the text, so something like this might do it (untested):

for my $td (@tds){
  my $bold = $td->look_down(_tag => q{b}); # look for a bold tag
  next unless $bold;
  my $txt = $bold->as_text;
  if ($txt=~ m/miR|let/){
    print $txt, qq{\n}; # if there is one print the text
  }
}
[download]

if I understand correctly, I can do something like this, to parse without download the web page...

#!/usr/local/bin/perl

use warnings;
use strict;
use LWP::Simple;

my $url="http://microrna.sanger.ac.uk/cgi-bin/targets/v5/detail_view.p
+l?transcript_id=ENST00000226253";
my $content=get ($url);
use HTML::TreeBuilder;

my $p = HTML::TreeBuilder->new;
$p->parse_content($content); # parse_content if you have a string

my @tds = $p->look_down(_tag => q{td}); # get a list of all the td tag
+s
for my $td (@tds){
  my $bold = $td->look_down(_tag => q{b}); # look for a bold tag
  if ($bold){
    print $bold->as_text, qq{\n}; # if there is one print the text
  }
}
$p->delete; # when you've finished with it
[download]

but I don't understand why it doesn't give back me nothing, it seems as the content of the page has no bold string...that impossible...I see them and If I download the page like before and then do the parsing...it works...could you explain me why :-(... thanks too much

...nothing...

Same here. :-(

I had more luck with LWP::UserAgent though

#!/usr/bin/perl

use warnings;
use strict;

use LWP::UserAgent;
use HTML::TreeBuilder;

my $url = q{http://microrna.sanger.ac.uk/cgi-bin/targets/v5/detail_vie
+w.pl?transcript_id=ENST00000226253};
 
my $ua = LWP::UserAgent->new;
$ua->timeout(10);

my $response = $ua->get($url);
 
my $content; 
if ($response->is_success) {
   $content = $response->content;
}
else {
   die $response->status_line;
}

my $p = HTML::TreeBuilder->new;
$p->parse_content($content);

my @tds = $p->look_down(_tag => q{td});
for my $td (@tds){
  my $bold = $td->look_down(_tag => q{b});
  next unless $bold;
  my $txt = $bold->as_text;
  if ($txt =~ /miR|let/){
    print $txt, qq{\n};
  }
}
$p->delete;
[download]

mmu-miR-705
mmu-miR-705
hsa-let-7d
hsa-let-7e
hsa-miR-483-5p
mmu-miR-683
hsa-miR-650
hsa-miR-920
mmu-miR-709
hsa-miR-26b*
hsa-miR-185
hsa-let-7a
hsa-miR-765
hsa-miR-629*
hsa-miR-19b-2*
hsa-miR-31
mmu-miR-707
hsa-miR-665
hsa-miR-339-5p
hsa-let-7c
hsa-let-7b
hsa-miR-7
hsa-miR-26b*
hsa-let-7g
hsa-miR-382
hsa-miR-454*
hsa-miR-501-5p
mmu-miR-666-5p
hsa-miR-486-3p
hsa-let-7f
mmu-miR-680
hsa-miR-219-2-3p
hsa-miR-153
hsa-miR-26a-2*
hsa-miR-328
hsa-miR-220c
hsa-miR-19a*
hsa-miR-433
hsa-miR-769-5p
hsa-miR-26b*
hsa-miR-19a*
hsa-miR-19b-1*
hsa-miR-25*
hsa-miR-483-5p
mmu-miR-685
hsa-miR-938
mmu-miR-465a-3p
hsa-miR-139-3p
hsa-miR-187*
mmu-miR-687
[download]

I'm no expert on LWP, perhaps the timeout? It took a while to download.