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