README.md

SemVer

The semver package provides the ability to work with Semantic Versions in Go. Specifically it provides the ability to:

• Parse semantic versions
• Sort semantic versions
• Check if a semantic version fits within a set of constraints
• Optionally work with a v prefix

Parsing Semantic Versions

To parse a semantic version use the NewVersion function. For example,

    v, err := semver.NewVersion("1.2.3-beta.1+build345")

If there is an error the version wasn't parseable. The version object has methods to get the parts of the version, compare it to other versions, convert the version back into a string, and get the original string. For more details please see the documentation.

Sorting Semantic Versions

A set of versions can be sorted using the sort package from the standard library. For example,

    raw := []string{"1.2.3", "1.0", "1.3", "2", "0.4.2",}
    vs := make([]*semver.Version, len(raw))
	for i, r := range raw {
		v, err := semver.NewVersion(r)
		if err != nil {
			t.Errorf("Error parsing version: %s", err)
		}

		vs[i] = v
	}

	sort.Sort(semver.Collection(vs))

Checking Version Constraints

Checking a version against version constraints is one of the most featureful parts of the package.

    c, err := semver.NewConstraint(">= 1.2.3")
    if err != nil {
        // Handle constraint not being parseable.
    }

    v, _ := semver.NewVersion("1.3")
    if err != nil {
        // Handle version not being parseable.
    }
    // Check if the version meets the constraints. The a variable will be true.
    a := c.Check(v)

Basic Comparisons

There are two elements to the comparisons. First, a comparison string is a list of comma separated and comparisons. These are then separated by || separated or comparisons. For example, ">= 1.2, < 3.0.0 || >= 4.2.3" is looking for a comparison that's greater than or equal to 1.2 and less than 3.0.0 or is greater than or equal to 4.2.3.

The basic comparisons are:

• =: equal (aliased to no operator)
• !=: not equal
• >: greater than
• <: less than
• >=: greater than or equal to
• <=: less than or equal to

Working With Pre-release Versions

Pre-releases, for those not familiar with them, are used for software releases prior to stable or generally available releases. Examples of pre-releases include development, alpha, beta, and release candidate releases. A pre-release may be a version such as 1.2.3-beta.1 while the stable release would be 1.2.3. In the order of precidence, pre-releases come before their associated releases. In this example 1.2.3-beta.1 < 1.2.3.

According to the Semantic Version specification pre-releases may not be API compliant with their release counterpart. It says,

A pre-release version indicates that the version is unstable and might not satisfy the intended compatibility requirements as denoted by its associated normal version.

SemVer comparisons without a pre-release comparator will skip pre-release versions. For example, >=1.2.3 will skip pre-releases when looking at a list of releases while >=1.2.3-0 will evaluate and find pre-releases.

The reason for the 0 as a pre-release version in the example comparison is because pre-releases can only contain ASCII alphanumerics and hyphens (along with . separators), per the spec. Sorting happens in ASCII sort order, again per the spec. The lowest character is a 0 in ASCII sort order (see an ASCII Table)

Understanding ASCII sort ordering is important because A-Z comes before a-z. That means >=1.2.3-BETA will return 1.2.3-alpha. What you might expect from case sensitivity doesn't apply here. This is due to ASCII sort ordering which is what the spec specifies.

Hyphen Range Comparisons

There are multiple methods to handle ranges and the first is hyphens ranges. These look like:

• 1.2 - 1.4.5 which is equivalent to >= 1.2, <= 1.4.5
• 2.3.4 - 4.5 which is equivalent to >= 2.3.4, <= 4.5

Wildcards In Comparisons

The x, X, and * characters can be used as a wildcard character. This works for all comparison operators. When used on the = operator it falls back to the pack level comparison (see tilde below). For example,

• 1.2.x is equivalent to >= 1.2.0, < 1.3.0
• >= 1.2.x is equivalent to >= 1.2.0
• <= 2.x is equivalent to <= 3
• * is equivalent to >= 0.0.0

Tilde Range Comparisons (Patch)

The tilde (~) comparison operator is for patch level ranges when a minor version is specified and major level changes when the minor number is missing. For example,

• ~1.2.3 is equivalent to >= 1.2.3, < 1.3.0
• ~1 is equivalent to >= 1, < 2
• ~2.3 is equivalent to >= 2.3, < 2.4
• ~1.2.x is equivalent to >= 1.2.0, < 1.3.0
• ~1.x is equivalent to >= 1, < 2

Caret Range Comparisons (Major)

The caret (^) comparison operator is for major level changes. This is useful when comparisons of API versions as a major change is API breaking. For example,

• ^1.2.3 is equivalent to >= 1.2.3, < 2.0.0
• ^1.2.x is equivalent to >= 1.2.0, < 2.0.0
• ^2.3 is equivalent to >= 2.3, < 3
• ^2.x is equivalent to >= 2.0.0, < 3

Validation

In addition to testing a version against a constraint, a version can be validated against a constraint. When validation fails a slice of errors containing why a version didn't meet the constraint is returned. For example,

    c, err := semver.NewConstraint("<= 1.2.3, >= 1.4")
    if err != nil {
        // Handle constraint not being parseable.
    }

    v, _ := semver.NewVersion("1.3")
    if err != nil {
        // Handle version not being parseable.
    }

    // Validate a version against a constraint.
    a, msgs := c.Validate(v)
    // a is false
    for _, m := range msgs {
        fmt.Println(m)

        // Loops over the errors which would read
        // "1.3 is greater than 1.2.3"
        // "1.3 is less than 1.4"
    }

Contribute

If you find an issue or want to contribute please file an issue or create a pull request.