#Assume the file is read to $str which contains
$str="iteration 1
        some information goes here
        machine name:[some meta-info]
                 some multi-line info
        machine name:[some meta-info]
                 some multi-line info
      iteration 2
        some information goes here
        machine name:[some meta-info]
                 some multi-line info
        machine name:[some meta-info]
                 some multi-line info";
$str=~s/(iteration)(.*)/<B> uc($1)$2 <\/B>/;
print $str;