feat(users/Profpatsch): add atomically-write

A little shell script to atomically write stdout to a file.

Change-Id: Icca58909c9ad3f92d69af2f5e20c08d69878a77c
Reviewed-on: https://cl.tvl.fyi/c/depot/+/3264
Tested-by: BuildkiteCI
Reviewed-by: Profpatsch <mail@profpatsch.de>
This commit is contained in:
Profpatsch 2021-08-01 18:41:18 +02:00
parent 1fbb960acf
commit 28bed07694

View file

@ -0,0 +1,28 @@
{ depot, pkgs, ... }:
# Atomically write a file (just `>` redirection in bash
# empties a file even if the command crashes).
#
# Maybe there is an existing tool for that?
# But its easy enough to implement.
#
# Example:
# atomically-write
# ./to
# echo "foo"
#
# will atomically write the string "foo" into ./to
let
atomically-write = pkgs.writers.writeDash "atomically-write" ''
set -e
to=$1
shift
# assumes that the tempfile is on the same file system, (or in memory)
# for the `mv` at the end to be more-or-less atomic.
tmp=$(${pkgs.coreutils}/bin/mktemp -d)
trap 'rm -r "$tmp"' EXIT
"$@" \
> "$tmp/out"
mv "$tmp/out" "$to"
'';
in atomically-write