composer/doc/articles/versions.md

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    tagline: Version constraints explained.
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# Versions

## Basic Constraints

### Exact

You can specify the exact version of a package. This will tell Composer to
install this version and this version only. If other dependencies require
a different version, the solver will ultimately fail and abort any install
or update procedures.

Example: `1.0.2`

### Range

By using comparison operators you can specify ranges of valid versions. Valid
operators are `>`, `>=`, `<`, `<=`, `!=`.

You can define multiple ranges. Ranges separated by a space (<code>&nbsp;</code>)
or comma (`,`) will be treated as a **logical AND**. A double pipe (`||`)
will be treated as a **logical OR**. AND has higher precedence than OR.

> **Note:** Be careful when using unbounded ranges as you might end up
> unexpectedly installing versions that break backwards compatibility.
> Consider using the [caret](#caret) operator instead for safety.

Examples:

* `>=1.0`
* `>=1.0 <2.0`
* `>=1.0 <1.1 || >=1.2`

### Range (Hyphen)

Inclusive set of versions. Partial versions on the right include are completed
with a wildcard. For example `1.0 - 2.0` is equivalent to `>=1.0.0 <2.1` as the
`2.0` becomes `2.0.*`. On the other hand `1.0.0 - 2.1.0` is equivalent to
`>=1.0.0 <=2.1.0`.

Example: `1.0 - 2.0`

### Wildcard

You can specify a pattern with a `*` wildcard. `1.0.*` is the equivalent of
`>=1.0 <1.1`.

Example: `1.0.*`

## Next Significant Release Operators

### Tilde

The `~` operator is best explained by example: `~1.2` is equivalent to
`>=1.2 <2.0.0`, while `~1.2.3` is equivalent to `>=1.2.3 <1.3.0`. As you can see
it is mostly useful for projects respecting [semantic
versioning](http://semver.org/). A common usage would be to mark the minimum
minor version you depend on, like `~1.2` (which allows anything up to, but not
including, 2.0). Since in theory there should be no backwards compatibility
breaks until 2.0, that works well. Another way of looking at it is that using
`~` specifies a minimum version, but allows the last digit specified to go up.

Example: `~1.2`

> **Note:** Though `2.0-beta.1` is strictly before `2.0`, a version constraint
> like `~1.2` would not install it. As said above `~1.2` only means the `.2`
> can change but the `1.` part is fixed.

> **Note:** The `~` operator has an exception on its behavior for the major
> release number. This means for example that `~1` is the same as `~1.0` as
> it will not allow the major number to increase trying to keep backwards
> compatibility.

### Caret

The `^` operator behaves very similarly but it sticks closer to semantic
versioning, and will always allow non-breaking updates. For example `^1.2.3`
is equivalent to `>=1.2.3 <2.0.0` as none of the releases until 2.0 should
break backwards compatibility. For pre-1.0 versions it also acts with safety
in mind and treats `^0.3` as `>=0.3.0 <0.4.0`.

This is the recommended operator for maximum interoperability when writing
library code.

Example: `^1.2.3`

## Stability

If you are using a constraint that does not explicitly define a stability,
Composer will default interally to `-dev` or `-stable`, depending on the
operator(s) used. This happens transparently.

If you wish to explicitly consider only the stable release in the comparison,
add the suffix `-stable`.

Examples:

 Constraint         | Internally
------------------- | ------------------------
 `1.2.3`            | `=1.2.3.0-stable`
 `>1.2`             | `>1.2.0.0-stable`
 `>=1.2`            | `>=1.2.0.0-dev`
 `>=1.2-stable`     | `>=1.2.0.0-stable`
 `<1.3`             | `<1.3.0.0-dev`
 `<=1.3`            | `<=1.3.0.0-stable`
 `1 - 2`            | `>=1.0.0.0-dev <3.0.0.0-dev`
 `~1.3`             | `>=1.3.0.0-dev <2.0.0.0-dev`
 `1.4.*`            | `>=1.4.0.0-dev <1.5.0.0-dev`

## Test version constraints

You can test version constraints using [semver.mwl.be](http://semver.mwl.be).
Fill in a package name and it will autofill the default version constraint
which Composer would add to your `composer.json` file. You can adjust the
version constraint and the tool will highlight all releases that match.