Searching code in a specific GitHub branch

Using console, I would search for specific code in a specific branch with the following

git grep 'my_search_text' my_branch

• my_branch should be available locally
• git grep can perform pattern matching of high complexity (see the documentation)

Not from the GitHub web interface itself, as mentioned in "How can I search for a commit message on GitHub?": only the default branch (generally master) is indexed.

Your best bet is to clone the repository, and there, search in all branches (with git log -S for instance).