Ok, you only want to do the search-and-replace if there is no word-spacing attribute in the HTML file. A way to do it is to create a variable $no_attr and set it to 1 if there's no word-spacing attribute in the file. The problem you have is that the file is in an array, and thus you have to iterate through it to determine if the attribute is present or not. A way to do it is to create a single string out of the array and check that string. Line 25 then becomes:

if (join('', @htmlLines) !~ m/word-spacing:\s?[\d]+px/ig) {
... rest of the code ...
[download]

Another way is to slurp the file into a single variable:

$/ = undef;
$html_file = <INFILE>
[download]

And do the search/replace on this string, all in one go. This is left as an exercise ;-)

Arjen