Enter this in the search box along with your search terms:
Get all gists from the user santisbon.
user:orenbochman
Find all gists with a .yml extension.
extension:yml
Find all gists with HTML files.
language:html
Find all gists with a ".bash_profile" file.
filename:.bash_profile
Excludes all results containing your search term.
NOT
Find gists with greater than 100 stars.
stars:>100
Include anonymous gists in your search.
anon:true
Search all forked gists for results.
fork:only
Find gists containing a file larger than 1000kbs.
size:>1000
Full code search: https://help.github.com/articles/searching-code/