A useful command to search contents within a Git repository is git grep:

$ git grep <pattern>

Example

For example, to see the files and lines where text is foo:

$ git grep foo

To also see line numbers:

$ git grep -n foo

To see only the files:

$ git grep -l foo

To search within commit reference(s):

$ git grep foo my_branch
$ git grep foo HEAD~3
$ git grep foo abc1234 def5678

To search with regex:

$ git grep -e "^foo"
$ git grep -e foo --or bar
$ git grep -e "^foo" --and -e "bar$"