preen
Pipe anything in
Give preen something on stdin and no file argument, and it renders it and
quits. No picker, no fzf.
git diff | preen # delta renders it
gh pr diff 42 | preen # so does a PR diff
cat NOTES.md | preen # glow renders it
preen - < NOTES.md # the same, said out loud
git diff | preen > out.txt # color is kept in the file too
A single - is the explicit form. It asks for the same behavior out loud,
which is what you want in a script where stdin might or might not be a pipe.
How it picks a renderer
It sniffs the content. In the first 200 lines it looks for the headers a unified diff always has:
- a
diff --gitline, or - an
@@ ... @@hunk header, or - a
---line and a+++line
Any one of those means delta. Anything else means glow.
The --- test needs +++ alongside it because markdown uses --- too — for
a horizontal rule, and for the top of a frontmatter block. On its own it would
send half your notes to delta.
The sniff strips ANSI escapes first. git diff --color=always paints its
own header lines, so without that step ^--- would never match and a colored
diff would be read as markdown. This works:
git diff --color=always | preen
Terminal or pipe
preen looks at where its own output is going:
- To a terminal — the result is paged through
less -R. Scroll, search with/, quit withq. - To a pipe or a file — the bytes are written plain, color and all.
That second case is deliberate. git diff | preen > out.txt keeps the color
in the file, so less -R out.txt later looks the same as it did live. So does
git diff | preen | head -40.
Layout
PREEN_LAYOUT=inline applies here too:
PREEN_LAYOUT=inline git diff | preen
There is no ctrl-s on this path — there is no picker to press it in — so the
environment variable is the only way to choose.
What it needs
Only the renderer it actually reaches for. A piped diff needs delta and does
not touch glow; piped markdown needs glow 3 or newer and does not touch
delta. Neither needs fzf, and neither needs to be in a git repository.
If stdin is empty, preen says nothing on stdin and exits rather than opening
an empty pager.
Where this is already wired up for you
The preen difftool in your git config is built on exactly this: it makes a
plain unified diff and pipes it into preen -. See
Git integration.