my $line = "<a href=\"/{HOST}?action\">123</a>:</b><br>".
           "[img-smile \"58-41\" \":)\"]";
my $var1 = "<img src=\"1-2.gif\" alt=\"[---]\">";
(my $var2) = $line =~ /(\[img-smile [^]]+\])/;
$line =~ s/$var2/$var1/;
print $line;