By default, Git sends its diff output (and generally any output that may be more than a screenful) to the system’s pager, which is a utility that prints only one screenful of output at a time. If you want to disable the pager when you run a command, pass --no-pager to Git:
$ git --no-pager <subcommand> <options>
This can be run for any Git command.
If you want to disable it by default for diff only, you can set the diff pager to cat by running:
$ git config pager.diff false
If you want to disable it by default for all commands, you can set the Git pager to cat by running:
$ git config --global core.pager cat