my $str = ' abc TXT efg TXT hig TXT';
print "Before: ",$str,"\n#########\n";
$str =~ s{(>)(.*?)(<)}
{
my ($tag_ends, $mydata, $tag_starts) = ($1,$2,$3);
$mydata =~ s/TXT/FOO/gs;
"$tag_ends$mydata$tag_starts"
}exgs;
print "After: ",$str,"\n#########\n";