Hi,

use Tk;
my $mw = tkinit;
my $t = $mw->Text()->pack;
$t->tagConfigure('foo', -background => 'yellow');
$t->insert('end',"foo\nbar\nbaz\nfoo\n");
$t->FindAll(qw/-exact -case foo/);
$t->tagAdd('foo',$t->tagRanges('sel'));
MainLoop;
[download]

See the tagRanges() and tagAdd() methods documented in Tk::Text

Cheers, Christoph
update: Added example