You can do this search using regular expressions (http://www.radsoftware.com.au/articles/regexlearnsyntax.aspx).

First, make sure to change the Search Mode to "Treat Query as a Regular Expression", then enter your search with the regular expression in the Query text box.

So in your example, if you wanted to find lines that end with "a=", you would enter "a=$" into the Query text box.

Hope that helps!