npm-install(1) -- Install a package
===================================

## SYNOPSIS

    npm install (with no args, in package dir)
    npm install [<@scope>/]<name>
    npm install [<@scope>/]<name>@<tag>
    npm install [<@scope>/]<name>@<version>
    npm install [<@scope>/]<name>@<version range>
    npm install <tarball file>
    npm install <tarball url>
    npm install <folder>

    alias: npm i
    common options: [-S|--save|-D|--save-dev|-O|--save-optional] [-E|--save-exact] [--dry-run]

## DESCRIPTION

This command installs a package, and any packages that it depends on. If the
package has a shrinkwrap file, the installation of dependencies will be driven
by that. See npm-shrinkwrap(1).

A `package` is:

* a) a folder containing a program described by a package.json file
* b) a gzipped tarball containing (a)
* c) a url that resolves to (b)
* d) a `<name>@<version>` that is published on the registry (see `npm-registry(7)`) with (c)
* e) a `<name>@<tag>` that points to (d)
* f) a `<name>` that has a "latest" tag satisfying (e)
* g) a `<git remote url>` that resolves to (a)

Even if you never publish your package, you can still get a lot of
benefits of using npm if you just want to write a node program (a), and
perhaps if you also want to be able to easily install it elsewhere
after packing it up into a tarball (b).


* `npm install` (in package directory, no arguments):

    Install the dependencies in the local node_modules folder.

    In global mode (ie, with `-g` or `--global` appended to the command),
    it installs the current package context (ie, the current working
    directory) as a global package.

    By default, `npm install` will install all modules listed as dependencies.
    With the `--production` flag (or when the `NODE_ENV` environment variable
    is set to `production`), npm will not install modules listed in
    `devDependencies`.

* `npm install <folder>`:

    Install a package that is sitting in a folder on the filesystem.

* `npm install <tarball file>`:

    Install a package that is sitting on the filesystem.  Note: if you just want
    to link a dev directory into your npm root, you can do this more easily by
    using `npm link`.

    Example:

          npm install ./package.tgz

* `npm install <tarball url>`:

    Fetch the tarball url, and then install it.  In order to distinguish between
    this and other options, the argument must start with "http://" or "https://"

    Example:

          npm install https://github.com/indexzero/forever/tarball/v0.5.6

* `npm install [<@scope>/]<name> [-S|--save|-D|--save-dev|-O|--save-optional]`:

    Do a `<name>@<tag>` install, where `<tag>` is the "tag" config. (See
    `npm-config(7)`.)

    In most cases, this will install the latest version
    of the module published on npm.

    Example:

          npm install sax

    `npm install` takes 3 exclusive, optional flags which save or update
    the package version in your main package.json:

    * `-S, --save`: Package will appear in your `dependencies`.

    * `-D, --save-dev`: Package will appear in your `devDependencies`.

    * `-O, --save-optional`: Package will appear in your `optionalDependencies`.

    When using any of the above options to save dependencies to your
    package.json, there is an additional, optional flag:

    * `-E, --save-exact`: Saved dependencies will be configured with an
      exact version rather than using npm's default semver range
      operator.

    Further, if you have an `npm-shrinkwrap.json` then it will be updated as
    well.

    `<scope>` is optional. The package will be downloaded from the registry
    associated with the specified scope. If no registry is associated with
    the given scope the default registry is assumed. See `npm-scope(7)`.

    Note: if you do not include the @-symbol on your scope name, npm will
    interpret this as a GitHub repository instead, see below. Scopes names
    must also be followed by a slash.

    Examples:

          npm install sax --save
          npm install githubname/reponame
          npm install @myorg/privatepackage
          npm install node-tap --save-dev
          npm install dtrace-provider --save-optional
          npm install readable-stream --save --save-exact


    **Note**: If there is a file or folder named `<name>` in the current
    working directory, then it will try to install that, and only try to
    fetch the package by name if it is not valid.

* `npm install [<@scope>/]<name>@<tag>`:

    Install the version of the package that is referenced by the specified tag.
    If the tag does not exist in the registry data for that package, then this
    will fail.

    Example:

          npm install sax@latest
          npm install @myorg/mypackage@latest

* `npm install [<@scope>/]<name>@<version>`:

    Install the specified version of the package.  This will fail if the
    version has not been published to the registry.

    Example:

          npm install sax@0.1.1
          npm install @myorg/privatepackage@1.5.0

* `npm install [<@scope>/]<name>@<version range>`:

    Install a version of the package matching the specified version range.  This
    will follow the same rules for resolving dependencies described in `package.json(5)`.

    Note that most version ranges must be put in quotes so that your shell will
    treat it as a single argument.

    Example:

          npm install sax@">=0.1.0 <0.2.0"
          npm install @myorg/privatepackage@">=0.1.0 <0.2.0"

* `npm install <git remote url>`:

    Installs the package from the hosted git provider, cloning it with
    `git`. First it tries via the https (git with github) and if that fails, via ssh.

          <protocol>://[<user>[:<password>]@]<hostname>[:<port>][:][/]<path>[#<commit-ish>]

    `<protocol>` is one of `git`, `git+ssh`, `git+http`, or
    `git+https`.  If no `<commit-ish>` is specified, then `master` is
    used.

    The following git environment variables are recognized by npm and will be added
    to the environment when running git:

    * `GIT_ASKPASS`
    * `GIT_PROXY_COMMAND`
    * `GIT_SSH`
    * `GIT_SSH_COMMAND`
    * `GIT_SSL_CAINFO`
    * `GIT_SSL_NO_VERIFY`

    See the git man page for details.

    Examples:

          npm install git+ssh://git@github.com:npm/npm.git#v1.0.27
          npm install git+https://isaacs@github.com/npm/npm.git
          npm install git://github.com/npm/npm.git#v1.0.27
          GIT_SSH_COMMAND='ssh -i ~/.ssh/custom_ident' npm install git+ssh://git@github.com:npm/npm.git

* `npm install <githubname>/<githubrepo>[#<commit-ish>]`:
* `npm install github:<githubname>/<githubrepo>[#<commit-ish>]`:

    Install the package at `https://github.com/githubname/githubrepo` by
    attempting to clone it using `git`.

    If you don't specify a *commit-ish* then `master` will be used.

    Examples:

          npm install mygithubuser/myproject
          npm install github:mygithubuser/myproject

* `npm install gist:[<githubname>/]<gistID>[#<commit-ish>]`:

    Install the package at `https://gist.github.com/gistID` by attempting to
    clone it using `git`. The GitHub username associated with the gist is
    optional and will not be saved in `package.json` if `-S` or `--save` is used.

    If you don't specify a *commit-ish* then `master` will be used.

    Example:

          npm install gist:101a11beef

* `npm install bitbucket:<bitbucketname>/<bitbucketrepo>[#<commit-ish>]`:

    Install the package at `https://bitbucket.org/bitbucketname/bitbucketrepo`
    by attempting to clone it using `git`.

    If you don't specify a *commit-ish* then `master` will be used.

    Example:

          npm install bitbucket:mybitbucketuser/myproject

* `npm install gitlab:<gitlabname>/<gitlabrepo>[#<commit-ish>]`:

    Install the package at `https://gitlab.com/gitlabname/gitlabrepo`
    by attempting to clone it using `git`.

    If you don't specify a *commit-ish* then `master` will be used.

    Example:

          npm install gitlab:mygitlabuser/myproject

You may combine multiple arguments, and even multiple types of arguments.
For example:

    npm install sax@">=0.1.0 <0.2.0" bench supervisor

The `--tag` argument will apply to all of the specified install targets. If a
tag with the given name exists, the tagged version is preferred over newer
versions.

The `--dry-run` argument will report in the usual way what the install would
have done without actually installing anything.

The `-f` or `--force` argument will force npm to fetch remote resources even if a
local copy exists on disk.

    npm install sax --force

The `-g` or `--global` argument will cause npm to install the package globally
rather than locally.  See `npm-folders(5)`.

The `--link` argument will cause npm to link global installs into the
local space in some cases.

The `--no-bin-links` argument will prevent npm from creating symlinks for
any binaries the package might contain.

The `--no-optional` argument will prevent optional dependencies from
being installed.

The `--no-shrinkwrap` argument, which will ignore an available
shrinkwrap file and use the package.json instead.

The `--nodedir=/path/to/node/source` argument will allow npm to find the
node source code so that npm can compile native modules.

The `--only={prod[uction]|dev[elopment]}` argument will cause either only
`devDependencies` or only non-`devDependencies` to be installed regardless of the `NODE_ENV`.

See `npm-config(7)`.  Many of the configuration params have some
effect on installation, since that's most of what npm does.

## ALGORITHM

To install a package, npm uses the following algorithm:

    load the existing node_modules tree from disk
    clone the tree
    fetch the package.json and assorted metadata and add it to the clone
    walk the clone and add any missing dependencies
      dependencies will be added as close to the top as is possible
      without breaking any other modules
    compare the original tree with the cloned tree and make a list of
    actions to take to convert one to the other
    execute all of the actions, deepest first
      kinds of actions are install, update, remove and move

For this `package{dep}` structure: `A{B,C}, B{C}, C{D}`,
this algorithm produces:

    A
    +-- B
    +-- C
    +-- D

That is, the dependency from B to C is satisfied by the fact that A
already caused C to be installed at a higher level. D is still installed
at the top level because nothing conflicts with it.

For `A{B,C}, B{C,D@1}, C{D@2}`, this algorithm produces:

    A
    +-- B
    +-- C
       `-- D@2
    +-- D@1

Because B's D@1 will be installed in the top level, C now has to install D@2
privately for itself.

See npm-folders(5) for a more detailed description of the specific
folder structures that npm creates.

### Limitations of npm's Install Algorithm

There are some very rare and pathological edge-cases where a cycle can
cause npm to try to install a never-ending tree of packages.  Here is
the simplest case:

    A -> B -> A' -> B' -> A -> B -> A' -> B' -> A -> ...

where `A` is some version of a package, and `A'` is a different version
of the same package.  Because `B` depends on a different version of `A`
than the one that is already in the tree, it must install a separate
copy.  The same is true of `A'`, which must install `B'`.  Because `B'`
depends on the original version of `A`, which has been overridden, the
cycle falls into infinite regress.

To avoid this situation, npm flat-out refuses to install any
`name@version` that is already present anywhere in the tree of package
folder ancestors.  A more correct, but more complex, solution would be
to symlink the existing version into the new location.  If this ever
affects a real use-case, it will be investigated.

## SEE ALSO

* npm-folders(5)
* npm-update(1)
* npm-link(1)
* npm-rebuild(1)
* npm-scripts(7)
* npm-build(1)
* npm-config(1)
* npm-config(7)
* npmrc(5)
* npm-registry(7)
* npm-tag(1)
* npm-rm(1)
* npm-shrinkwrap(1)
