How to make git diff write to stdout?

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

The following core.pager value uses less, which prints to stdout, and also has pager functionality (if required), enabling scrolling up and down (unlike cat):

$ git config --global core.pager "less -FRSX"

It immediately quits if the diff fits on the first screen (-F), outputs raw control characters (-R), chops long lines rather than wrapping (-S), and does not use termcap init/deinit strings (-X).

You can also simply use cat for any git command if you don't care about the colors.

So git diff | cat for your case.

Edit: as pointed out in the comments if you do care about the colors use:

git diff --color | cat