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nix-hash
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1
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Nix
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nix-hash
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compute the cryptographic hash of a path
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nix-hash
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\--flat
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\--base32
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\--truncate
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\--type
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hashAlgo
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path
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nix-hash
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\--to-base16
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hash
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nix-hash
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\--to-base32
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hash
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# Description
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The command `nix-hash` computes the cryptographic hash of the contents
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of each *path* and prints it on standard output. By default, it computes
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an MD5 hash, but other hash algorithms are available as well. The hash
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is printed in hexadecimal. To generate the same hash as
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`nix-prefetch-url` you have to specify multiple arguments, see below for
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an example.
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The hash is computed over a *serialisation* of each path: a dump of the
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file system tree rooted at the path. This allows directories and
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symlinks to be hashed as well as regular files. The dump is in the *NAR
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format* produced by [`nix-store` `--dump`](#refsec-nix-store-dump).
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Thus, `nix-hash
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path` yields the same cryptographic hash as `nix-store --dump
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path | md5sum`.
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# Options
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- `--flat`
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Print the cryptographic hash of the contents of each regular file
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*path*. That is, do not compute the hash over the dump of *path*.
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The result is identical to that produced by the GNU commands
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`md5sum` and `sha1sum`.
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- `--base32`
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Print the hash in a base-32 representation rather than hexadecimal.
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This base-32 representation is more compact and can be used in Nix
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expressions (such as in calls to `fetchurl`).
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- `--truncate`
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Truncate hashes longer than 160 bits (such as SHA-256) to 160 bits.
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- `--type` *hashAlgo*
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Use the specified cryptographic hash algorithm, which can be one of
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`md5`, `sha1`, and `sha256`.
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- `--to-base16`
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Don’t hash anything, but convert the base-32 hash representation
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*hash* to hexadecimal.
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- `--to-base32`
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Don’t hash anything, but convert the hexadecimal hash representation
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*hash* to base-32.
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# Examples
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Computing the same hash as `nix-prefetch-url`:
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$ nix-prefetch-url file://<(echo test)
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1lkgqb6fclns49861dwk9rzb6xnfkxbpws74mxnx01z9qyv1pjpj
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$ nix-hash --type sha256 --flat --base32 <(echo test)
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1lkgqb6fclns49861dwk9rzb6xnfkxbpws74mxnx01z9qyv1pjpj
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Computing hashes:
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$ mkdir test
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$ echo "hello" > test/world
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$ nix-hash test/ (MD5 hash; default)
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8179d3caeff1869b5ba1744e5a245c04
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$ nix-store --dump test/ | md5sum (for comparison)
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8179d3caeff1869b5ba1744e5a245c04 -
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$ nix-hash --type sha1 test/
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e4fd8ba5f7bbeaea5ace89fe10255536cd60dab6
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$ nix-hash --type sha1 --base32 test/
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nvd61k9nalji1zl9rrdfmsmvyyjqpzg4
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$ nix-hash --type sha256 --flat test/
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error: reading file `test/': Is a directory
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$ nix-hash --type sha256 --flat test/world
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5891b5b522d5df086d0ff0b110fbd9d21bb4fc7163af34d08286a2e846f6be03
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Converting between hexadecimal and base-32:
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$ nix-hash --type sha1 --to-base32 e4fd8ba5f7bbeaea5ace89fe10255536cd60dab6
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nvd61k9nalji1zl9rrdfmsmvyyjqpzg4
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$ nix-hash --type sha1 --to-base16 nvd61k9nalji1zl9rrdfmsmvyyjqpzg4
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e4fd8ba5f7bbeaea5ace89fe10255536cd60dab6
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