nix-hash - Man Page

nix-hash [--flat] [--base32] [--truncate] [--type hashAlgo] path...

nix-hash --to-base16 hash...

nix-hash --to-base32 hash...

The command nix-hash computes the cryptographic hash of the contents of each path and prints it on standard output​. By default, it computes an MD5 hash, but other hash algorithms are available as well​. The hash is printed in hexadecimal​. To generate the same hash as nix-prefetch-url you have to specify multiple arguments, see below for an example​.

The hash is computed over a serialisation of each path: a dump of the file system tree rooted at the path​. This allows directories and symlinks to be hashed as well as regular files​. The dump is in the NAR format produced by nix-store --dump​. Thus, nix-hash path yields the same cryptographic hash as nix-store --dump path | md5sum​.

--flat

Print the cryptographic hash of the contents of each regular file path​. That is, do not compute the hash over the dump of path​. The result is identical to that produced by the GNU commands md5sum and sha1sum​.

--base32

Print the hash in a base-32 representation rather than hexadecimal​. This base-32 representation is more compact and can be used in Nix expressions (such as in calls to fetchurl)​.

--truncate

Truncate hashes longer than 160 bits (such as SHA-256) to 160 bits​.

--type hashAlgo

Use the specified cryptographic hash algorithm, which can be one of md5, sha1, and sha256​.

--to-base16

Don’t hash anything, but convert the base-32 hash representation hash to hexadecimal​.

--to-base32

Don’t hash anything, but convert the hexadecimal hash representation hash to base-32​.

Computing the same hash as nix-prefetch-url:

$ nix-prefetch-url file://<(echo test)
1lkgqb6fclns49861dwk9rzb6xnfkxbpws74mxnx01z9qyv1pjpj
$ nix-hash --type sha256 --flat --base32 <(echo test)
1lkgqb6fclns49861dwk9rzb6xnfkxbpws74mxnx01z9qyv1pjpj

Computing hashes:

$ mkdir test
$ echo "hello" > test/world

$ nix-hash test/ (MD5 hash; default)
8179d3caeff1869b5ba1744e5a245c04

$ nix-store --dump test/ | md5sum (for comparison)
8179d3caeff1869b5ba1744e5a245c04  -

$ nix-hash --type sha1 test/
e4fd8ba5f7bbeaea5ace89fe10255536cd60dab6

$ nix-hash --type sha1 --base32 test/
nvd61k9nalji1zl9rrdfmsmvyyjqpzg4

$ nix-hash --type sha256 --flat test/
error: reading file `test/': Is a directory

$ nix-hash --type sha256 --flat test/world
5891b5b522d5df086d0ff0b110fbd9d21bb4fc7163af34d08286a2e846f6be03

Converting between hexadecimal and base-32:

$ nix-hash --type sha1 --to-base32 e4fd8ba5f7bbeaea5ace89fe10255536cd60dab6
nvd61k9nalji1zl9rrdfmsmvyyjqpzg4

$ nix-hash --type sha1 --to-base16 nvd61k9nalji1zl9rrdfmsmvyyjqpzg4
e4fd8ba5f7bbeaea5ace89fe10255536cd60dab6

Eelco Dolstra

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