Is (?#...) recent? Alternatives:

/(?:)$pat/

/(?:$pat)/

my $re = qr/$pat/;
/$re/
[download]

I'd always used (?:) before, but I'd forgotten how to spell it and found (?#) in the Perl 5.14 documentation. I couldn't find it in a modern perldelta though.

Now I have the code here, and I tried to apply another logical solution (your solution works!), but it don't work, do you know where is my fail now ?

My original code was:

sub casa_ruta
{
        my ($r, $ruta,$exactly)=@_;

# avoid empty patern
#       if (length ($ruta) == 0)
#       {
#               $ruta=".";
#       }
        if (defined $exactly)
        {
                if ($r eq $ruta)
                {
                        return 1;       
                }
        }
        else
        {
                if ($r =~ /$ruta/i)
                {
                        return 1;
                }
        }
        return 0;
}
[download]

sub casa_ruta
{
        my ($r, $ruta,$exactly)=@_;


        if ("r" =~ /(r)/)
        {
                ;
        }
        else
        {
                print STDERR "BUG\n";
        }
        #print STDERR "$fix_re";

#       if (length ($ruta) == 0)
#       {
#               $ruta=".";
#       }
        if (defined $exactly)
        {
                if ($r eq $ruta)
                {
                        return 1;       
                }
        }
        else
        {
          if ("r" =~ /(r)/)
          {
                 ;
          }
          else
          {
                print STDERR "BUG2\n";
          }
                if ($r =~ /$ruta/i)
                {
                        return 1;
                }
                else
                {
                        printf STDERR "BUG ('$r','$ruta')\n";
                        printf STDERR join (",",caller);
                        exit 1;
                }
        }
        return 0;
}
[download]

But It print in STDERR :

BUG ('/my/path','')

My::Module,/path/to/myfile.pm,1181

and exits

Effectively with /(?:)$ruta/i it is working ... but I would like to understand this issue

UPDATE:

See my next debug trace:

  DB<1> c 152
... #my script output here
main::ejecutar_sae_appfinder(/srv/www/sae_appfinder/index.pl:152):
152:            %nodos_tomcats=buscar_ruta_tomcats ($p_ruta,\%apaches,
+\%tomcats,$search_tomcathost);
  DB<2> s
Sae::Inventario::buscar_ruta_tomcats(/opt/scripts/perl/Sae/Inventario.
+pm:1181):
1181:        my ($ruta,$apaches,$tomcats,$search_tomcathost)=@_;
  DB<2> c casar_ruta
Subroutine Sae::Inventario::casar_ruta not found.
  DB<3> c casa_ruta
Sae::Inventario::casa_ruta(/opt/scripts/perl/Sae/Inventario.pm:91):
91:        my ($r, $ruta,$exactly)=@_;
  DB<4> x @_
0  ''
1  ''
  DB<5> n
Sae::Inventario::casa_ruta(/opt/scripts/perl/Sae/Inventario.pm:94):
94:        if ("r" =~ /(r)/)
95:        {
  DB<5> p "$r" =~ /$ruta/
1<label><input type="radio" name="format" value="html" checked="checke
+d" />html</label><label><input type="radio" name="format" value="odt"
+ />odt</label><br><input type="submit" name="consultar" value="consul
+tar" /><div><input type="hidden" name=".cgifields" value="info"  /><i
+nput type="hidden" name=".cgifields" value="format"  /><input type="h
+idden" name=".cgifields" value="entorno"  /></div></form></div>
  DB<6> p "$r" =~ /$ruta/
1
  DB<7> n
Sae::Inventario::casa_ruta(/opt/scripts/perl/Sae/Inventario.pm:108):
108:        if (defined $exactly)
109:        {
  DB<7> p "$r" =~ /$ruta/

  DB<8>
[download]

In DB<5> html code is printed here (If I add in the begin of script "$|=1;" it doesn't appear If I understand TFM "r" =~ /(r)/ should make $xx =~ // return true, isn't it?

ok, so I reread the doc, and I understand it. With my proposed solution, i was using "/(r)/" pattern, so it was not working.
It is not very intuitive, but it is ok
Sorry wasting your time and a big thank for you

Sorry wasting your time and a big thank for you

I didn't actually help, but You learned about The empty pattern // and improved your bug report abilities -- not a waste of time :)