I've run into this a few times when a site serves a variable file i try to download
wget http://trac-hacks.org/changeset/latest/tracajaxcommentsplugin?old_path=/&filename=tracajaxcommentsplugin&format=zip
Expected file
tracajaxcommentsplugin-r10913.zip
instead I get a file
tracajaxcommentsplugin\?old_path\=%2F
with content
<!DOCTYPE html
PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" lang="en" ...
This problem is not specific to trac or this pecific file.
Wrap it with a single quote:
$ wget 'http://trac-hacks.org/changeset/latest/tracajaxcommentsplugin?old_path=/&filename=tracajaxcommentsplugin&format=zip' -O tracajaxcommentsplugin-r10913.zip