$str = "%tag1% went to %tag2% 
#with
$str = ~ s/\%(\S+)\%/$template{$1}/gi; 

##</code><code>##

$str = "%tag1%ALONGSTRINGOFTEXT%tag2% 
#with
$str = ~ s/\%(\S+)\%/$template{$1}/gi; 

#would yield:
#$str eq $template{"tag1%ALONGSTRINGOFTEXT%tag2"};