fetch

README

fetch

fetch makes it easy to download files, folders, or release assets from a specific commit, branch, or tag of a public or private GitHub repo.

Motivation

Gruntwork helps software teams get up and running on AWS with DevOps best practices and world-class infrastructure in about a day. Sometimes we publish scripts and binaries that clients use in their infrastructure, and we want an easy way to install a specific version of one of those scripts and binaries. While this is fairly straightforward to do with public GitHub repos, as you can usually curl or wget a public URL, it's much trickier to do with private GitHub repos, as you have to make multiple API calls, parse JSON responses, and handle authentication. Fetch makes it possible to handle all of these cases with a one-liner.

Features

• Download from a specific git tag, branch, or commit SHA.
• Download a single file, a subset of files, or all files from the repo.
• Download one or more binary assets from a specific release that match a regular expression.
• Verify the SHA256 or SHA512 checksum of a binary asset.
• Download from public repos, or from private repos by specifying a GitHub Personal Access Token.
• Download from GitHub Enterprise.
• When specifying a git tag, you can can specify either exactly the tag you want, or a Tag Constraint Expression to do things like "get the latest non-breaking version" of this repo. Note that fetch assumes git tags are specified according to Semantic Versioning principles.

Quick examples

Download folder /baz from tag 0.1.3 of a GitHub repo and save it to /tmp/baz:

fetch --repo="https://github.com/foo/bar" --tag="0.1.3" --source-path="/baz" /tmp/baz

Download a release asset matching named foo.exe from release 0.1.5 and save them to /tmp:

fetch --repo="https://github.com/foo/bar" --tag="0.1.5" --release-asset="foo.exe" /tmp

Download all release assets matching the regular expression, foo_linux-.* from release 0.1.5 and save them to /tmp:

fetch --repo="https://github.com/foo/bar" --tag="0.1.5" --release-asset="foo_linux-.*" /tmp

See more examples in the Examples section.

Installation

Download the fetch binary from the GitHub Releases tab.

Usage

Assumptions

fetch assumes that a repo's tags are in the format vX.Y.Z or X.Y.Z to support Semantic Versioning parsing. This allows you to specify a Tag Constraint Expression to do things like "get the latest non-breaking version" of this repo. Note that fetch also allows downloading a specific tag not in SemVer format.

General Usage

fetch [OPTIONS] <local-download-path>

The supported options are:

• --repo (Required): The fully qualified URL of the GitHub repo to download from (e.g. https://github.com/foo/bar).
• --tag (Optional): The git tag to download. Can be a specific tag or a Tag Constraint Expression.
• --branch (Optional): The git branch from which to download; the latest commit in the branch will be used. If specified, will override --tag.
• --commit (Optional): The SHA of a git commit to download. If specified, will override --branch and --tag.
• --source-path (Optional): The source path to download from the repo (e.g. --source-path=/folder will download the /folder path and all files below it). By default, all files are downloaded from the repo unless --source-path or --release-asset is specified. This option can be specified more than once.
• --release-asset (Optional): A regular expression matching release assets--these are binary files uploaded to a GitHub Release--to download. It only works with the --tag option.
• --release-asset-checksum (Optional): The checksum that a release asset should have. Fetch will fail if this value is non-empty and does not match the checksum computed by Fetch, or if more than 1 assets are matched by the release-asset regular expression.
• --release-asset-checksum-algo (Optional): The algorithm fetch will use to compute a checksum of the release asset. Supported values are sha256 and sha512.
• --github-oauth-token (Optional): A GitHub Personal Access Token. Required if you're downloading from private GitHub repos. NOTE: fetch will also look for this token using the GITHUB_OAUTH_TOKEN environment variable, which we recommend using instead of the command line option to ensure the token doesn't get saved in bash history.
• --github-api-version (Optional): Used when fetching an artifact from a GitHub Enterprise instance. Defaults to v3. This is ignored when fetching from GitHub.com.

The supported arguments are:

• <local-download-path> (Required): The local path where all files should be downloaded (e.g. /tmp).

Run fetch --help to see more information about the flags.

Tag Constraint Expressions

The value of --tag can be expressed using any operators defined in hashicorp/go-version.

Specifically, this includes:

Tag Constraint Pattern	Meaning
1.0.7	Exactly version 1.0.7
=1.0.7	Exactly version 1.0.7
!=1.0.7	The latest version as long as that version is not 1.0.7
>1.0.7	The latest version greater than 1.0.7
<1.0.7	The latest version that's less than 1.0.7
>=1.0.7	The latest version greater than or equal to 1.0.7
<=1.0.7	The latest version that's less than or equal to 1.0.7
~>1.0.7	The latest version that is greater than 1.0.7 and less than 1.1.0
~>1.0	The latest version that is greater than 1.0 and less than 2.0

Examples

Usage Example 1

Download /modules/foo/bar.sh from a GitHub release where the tag is the latest version of 0.1.x but at least 0.1.5, and save it to /tmp/bar:

fetch --repo="https://github.com/foo/bar" --tag="~>0.1.5" --source-path="/modules/foo/bar.sh" /tmp/bar

Usage Example 2

Download all files in /modules/foo from a GitHub release where the tag is exactly 0.1.5, and save them to /tmp:

fetch --repo="https://github.com/foo/bar" --tag="0.1.5" --source-path="/modules/foo" /tmp

Usage Example 3

Download all files from a private GitHub repo using the GitHUb oAuth Token 123. Get the release whose tag is exactly 0.1.5, and save the files to /tmp:

GITHUB_OAUTH_TOKEN=123

fetch --repo="https://github.com/foo/bar" --tag="0.1.5" /tmp

Usage Example 4

Download all files from the latest commit on the sample-branch branch, and save them to /tmp:

fetch --repo="https://github.com/foo/bar" --branch="sample-branch" /tmp/josh1

Usage Example 5

Download all files from the git commit f32a08313e30f116a1f5617b8b68c11f1c1dbb61, and save them to /tmp:

fetch --repo="https://github.com/foo/bar" --commit="f32a08313e30f116a1f5617b8b68c11f1c1dbb61" /tmp/josh1

Usage Example 6

Download the release asset foo.exe from a GitHub release where the tag is exactly 0.1.5, and save it to /tmp:

fetch --repo="https://github.com/foo/bar" --tag="0.1.5" --release-asset="foo.exe" /tmp

Usage Example 7

Download the release asset foo.exe from a GitHub release hosted on a GitHub Enterprise instance running at ghe.mycompany.com where the tag is exactly 0.1.5, and save it to /tmp:

fetch --repo="https://ghe.mycompany.com/foo/bar" --tag="0.1.5" --release-asset="foo.exe" /tmp

License

This code is released under the MIT License. See LICENSE.txt.

TODO

• Introduce code verification using something like GPG signatures or published checksums
• Explicitly test for exotic repo and org names
• Apply stricter parsing for repo-filter command-line arg