brew livecheck

The brew livecheck command finds the newest version of a formula or cask’s software by checking upstream. Livecheck has strategies to identify versions from various sources, such as Git repositories, websites, etc.

Behavior

When livecheck isn’t given instructions for how to check for upstream versions, it does the following by default:

  1. For formulae: Collect the head, stable, and homepage URLs, in that order. For casks: Collect the url and homepage URLs, in that order.
  2. Determine if any strategies apply to the first URL. If not, try the next URL.
  3. If a strategy can be applied, use it to check for new versions.
  4. Return the newest version (or an error if versions could not be found at any available URLs).

It’s sometimes necessary to override this default behavior to create a working check for a formula/cask. If a source doesn’t provide the newest version, we need to check a different one. If livecheck doesn’t correctly match version text, we need to provide an appropriate regex.

This can be accomplished by adding a livecheck block to the formula/cask. For more information on the available methods, please refer to the Livecheck class documentation.

Creating a check

  1. Use the debug output to understand the situation. brew livecheck --debug <formula>|<cask> provides information about which URLs livecheck tries, any strategies that apply, matched versions, etc.

  2. Research available sources to select a URL. Try removing the file name from stable/url, to see if this is a directory listing page. If that doesn’t work, try to find a page that links to the file (e.g. a download page). If it’s not possible to find the newest version on the website, try checking other sources from the formula/cask. When necessary, search for other sources outside of the formula/cask.

  3. Create a regex, if necessary. If the check works without a regex and wouldn’t benefit from having one, it’s usually fine to omit it. More information on creating regexes can be found in the regex guidelines section.

General guidelines

URL guidelines

Regex guidelines

The livecheck block regex restricts matches to a subset of the fetched content and uses a capture group around the version text.

Example livecheck blocks

The following examples cover a number of patterns that you may encounter. These are intended to be representative samples and can be easily adapted.

When in doubt, start with one of these examples instead of copy-pasting a livecheck block from a random formula/cask.

File names

  livecheck do
    url "https://www.example.com/downloads/"
    regex(/href=.*?example[._-]v?(\d+(?:\.\d+)+)\.t/i)
  end

When matching the version from a file name on an HTML page, we often restrict matching to href attributes. href=.*? will match the opening delimiter (", ') as well as any part of the URL before the file name.

We sometimes make this more explicit to exclude unwanted matches. URLs with a preceding path can use href=.*?/ and others can use href=["']?. For example, this is necessary when the page also contains unwanted files with a longer prefix (another-example-1.2.tar.gz).

Version directories

  livecheck do
    url "https://www.example.com/releases/example/"
    regex(%r{href=["']?v?(\d+(?:\.\d+)+)/?["' >]}i)
  end

When checking a directory listing page, sometimes files are separated into version directories (e.g. 1.2.3/). In this case, we must identify versions from the directory names.

Git tags

  livecheck do
    url :stable
    regex(/^v?(\d+(?:\.\d+)+)$/i)
  end

When the stable URL uses the Git strategy, the regex above will only match tags like 1.2/v1.2, etc.

If tags include the software name as a prefix (e.g. example-1.2.3), it’s easy to modify the regex accordingly: /^example[._-]v?(\d+(?:\.\d+)+)$/i

PageMatch strategy block

  livecheck do
    url :homepage
    regex(/href=.*?example[._-]v?(\d{4}-\d{2}-\d{2})\.t/i)
    strategy :page_match do |page, regex|
      page.scan(regex).map { |match| match&.first&.gsub(/\D/, "") }
    end
  end

When necessary, a strategy block allows us to have greater flexibility in how upstream version information is matched and processed. Currently, they’re only used when the upstream version format needs to be manipulated to match the formula/cask format. In the example above, we’re converting a date format like 2020-01-01 into 20200101.

The PageMatch strategy block style seen here also applies to any strategy that uses PageMatch internally.

Git strategy block

  livecheck do
    url :stable
    regex(/^(\d{4}-\d{2}-\d{2})$/i)
    strategy :git do |tags, regex|
      tags.map { |tag| tag[regex, 1]&.gsub(/\D/, "") }.compact
    end
  end

A strategy block for Git is a bit different, as the block receives an array of tag strings instead of a page content string. Similar to the PageMatch example, this is converting tags with a date format like 2020-01-01 into 20200101.

Skip

  livecheck do
    skip "No version information available"
  end

Livecheck automatically skips some formulae/casks for a number of reasons (deprecated, disabled, discontinued, etc.). However, on rare occasions we need to use a livecheck block to do a manual skip. The skip method takes a string containing a very brief reason for skipping.

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