'\" t
.\"     Title: nix-hash
.\"    Author: Eelco Dolstra
.\" Generator: DocBook XSL Stylesheets v1.79.2 <http://docbook.sf.net/>
.\"      Date: 12/12/2020
.\"    Manual: Command Reference
.\"    Source: Nix 2.3.7
.\"  Language: English
.\"
.TH "NIX\-HASH" "1" "12/12/2020" "Nix 2\&.3\&.7" "Command Reference"
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.SH "NAME"
nix-hash \- compute the cryptographic hash of a path
.SH "SYNOPSIS"
.HP \w'\fBnix\-hash\fR\ 'u
\fBnix\-hash\fR [\fB\-\-flat\fR] [\fB\-\-base32\fR] [\fB\-\-truncate\fR] [\fB\-\-type\fR\ \fIhashAlgo\fR] \fIpath\fR...
.HP \w'\fBnix\-hash\fR\ 'u
\fBnix\-hash\fR \fB\-\-to\-base16\fR \fIhash\fR...
.HP \w'\fBnix\-hash\fR\ 'u
\fBnix\-hash\fR \fB\-\-to\-base32\fR \fIhash\fR...
.SH "DESCRIPTION"
.PP
The command
\fBnix\-hash\fR
computes the cryptographic hash of the contents of each
\fIpath\fR
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
\fBnix\-prefetch\-url\fR
you have to specify multiple arguments, see below for an example\&.
.PP
The hash is computed over a
\fIserialisation\fR
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
\fINAR format\fR
produced by
\fBnix\-store\fR \fB\-\-dump\fR\&. Thus,
nix\-hash \fIpath\fR
yields the same cryptographic hash as
nix\-store \-\-dump \fIpath\fR | md5sum\&.
.SH "OPTIONS"
.PP
\fB\-\-flat\fR
.RS 4
Print the cryptographic hash of the contents of each regular file
\fIpath\fR\&. That is, do not compute the hash over the dump of
\fIpath\fR\&. The result is identical to that produced by the GNU commands
\fBmd5sum\fR
and
\fBsha1sum\fR\&.
.RE
.PP
\fB\-\-base32\fR
.RS 4
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
\fBfetchurl\fR)\&.
.RE
.PP
\fB\-\-truncate\fR
.RS 4
Truncate hashes longer than 160 bits (such as SHA\-256) to 160 bits\&.
.RE
.PP
\fB\-\-type\fR \fIhashAlgo\fR
.RS 4
Use the specified cryptographic hash algorithm, which can be one of
md5,
sha1, and
sha256\&.
.RE
.PP
\fB\-\-to\-base16\fR
.RS 4
Don\(cqt hash anything, but convert the base\-32 hash representation
\fIhash\fR
to hexadecimal\&.
.RE
.PP
\fB\-\-to\-base32\fR
.RS 4
Don\(cqt hash anything, but convert the hexadecimal hash representation
\fIhash\fR
to base\-32\&.
.RE
.SH "EXAMPLES"
.PP
Computing the same hash as
\fBnix\-prefetch\-url\fR:
.sp
.if n \{\
.RS 4
.\}
.nf
$ nix\-prefetch\-url file://<(echo test)
1lkgqb6fclns49861dwk9rzb6xnfkxbpws74mxnx01z9qyv1pjpj
$ nix\-hash \-\-type sha256 \-\-flat \-\-base32 <(echo test)
1lkgqb6fclns49861dwk9rzb6xnfkxbpws74mxnx01z9qyv1pjpj
.fi
.if n \{\
.RE
.\}
.PP
Computing hashes:
.sp
.if n \{\
.RS 4
.\}
.nf
$ 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/\*(Aq: Is a directory

$ nix\-hash \-\-type sha256 \-\-flat test/world
5891b5b522d5df086d0ff0b110fbd9d21bb4fc7163af34d08286a2e846f6be03
.fi
.if n \{\
.RE
.\}
.PP
Converting between hexadecimal and base\-32:
.sp
.if n \{\
.RS 4
.\}
.nf
$ nix\-hash \-\-type sha1 \-\-to\-base32 e4fd8ba5f7bbeaea5ace89fe10255536cd60dab6
nvd61k9nalji1zl9rrdfmsmvyyjqpzg4

$ nix\-hash \-\-type sha1 \-\-to\-base16 nvd61k9nalji1zl9rrdfmsmvyyjqpzg4
e4fd8ba5f7bbeaea5ace89fe10255536cd60dab6
.fi
.if n \{\
.RE
.\}
.sp
.SH "AUTHOR"
.PP
\fBEelco Dolstra\fR
.RS 4
Author
.RE
.SH "COPYRIGHT"
.br
Copyright \(co 2004-2018 Eelco Dolstra
.br