As I explained above, you can’t put the assignment $line = $newline; inside the while loop, because updating $line resets the /g match position to the beginning of the string, creating an infinite loop. I tested my code before posting, and when the assignment $line = $newline; occurs after (i.e., outside) the inner loop, the tied file is updated correctly.

I suspect your current problem is that the regex match is failing. In light of your subsequent post, it appears your data file never contains a string matching / Name=(.*?) \s+ Password=(.*?) (?:\s+|$) /mx. You will need to adapt the while loop regex to the actual format of the data in the input file. For example (untested):

while ($line =~ / < Node \.*? Name="(.*?)" Type=".*?" Descr=".*?" Icon
+=".*?" Panel=".*?" Username=".*?" Domain=".*?" Password="(.*?)" .*? >
+ /mgx)
[download]

or just:

while ($line =~ / < Node \.*? Name="(.*?)" .*? Password="(.*?)" .*? > 
+/mgx)
[download]

Update (25^th November, 2015): Changed / < \s* Name= to / < Node .*? Name= in each regex.

Hope that helps,