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npm-scripts(7) -- How npm handles the "scripts" field
=====================================================
## DESCRIPTION
npm supports the "scripts" property of the package.json script, for the
following scripts:
* prepublish:
Run BEFORE the package is published. (Also run on local `npm
install` without any arguments.)
* publish, postpublish:
Run AFTER the package is published.
* preinstall:
Run BEFORE the package is installed
* install, postinstall:
Run AFTER the package is installed.
* preuninstall, uninstall:
Run BEFORE the package is uninstalled.
* postuninstall:
Run AFTER the package is uninstalled.
* preversion, version:
Run BEFORE bump the package version.
* postversion:
Run AFTER bump the package version.
* pretest, test, posttest:
Run by the `npm test` command.
* prestop, stop, poststop:
Run by the `npm stop` command.
* prestart, start, poststart:
Run by the `npm start` command.
* prerestart, restart, postrestart:
Run by the `npm restart` command. Note: `npm restart` will run the
stop and start scripts if no `restart` script is provided.
Additionally, arbitrary scripts can be executed by running `npm
run-script <stage>`. *Pre* and *post* commands with matching
names will be run for those as well (e.g. `premyscript`, `myscript`,
`postmyscript`).
## COMMON USES
If you need to perform operations on your package before it is used, in a way
that is not dependent on the operating system or architecture of the
target system, use a `prepublish` script. This includes
tasks such as:
* Compiling CoffeeScript source code into JavaScript.
* Creating minified versions of JavaScript source code.
* Fetching remote resources that your package will use.
The advantage of doing these things at `prepublish` time is that they can be done once, in a
single place, thus reducing complexity and variability.
Additionally, this means that:
* You can depend on `coffee-script` as a `devDependency`, and thus
your users don't need to have it installed.
* You don't need to include minifiers in your package, reducing
the size for your users.
* You don't need to rely on your users having `curl` or `wget` or
other system tools on the target machines.
## DEFAULT VALUES
npm will default some script values based on package contents.
* `"start": "node server.js"`:
If there is a `server.js` file in the root of your package, then npm
will default the `start` command to `node server.js`.
* `"install": "node-gyp rebuild"`:
If there is a `binding.gyp` file in the root of your package and you
haven't defined your own `install` or `preinstall` scripts, npm will
default the `install` command to compile using node-gyp.
## USER
If npm was invoked with root privileges, then it will change the uid
to the user account or uid specified by the `user` config, which
defaults to `nobody`. Set the `unsafe-perm` flag to run scripts with
root privileges.
## ENVIRONMENT
Package scripts run in an environment where many pieces of information
are made available regarding the setup of npm and the current state of
the process.
### path
If you depend on modules that define executable scripts, like test
suites, then those executables will be added to the `PATH` for
executing the scripts. So, if your package.json has this:
{ "name" : "foo"
, "dependencies" : { "bar" : "0.1.x" }
, "scripts": { "start" : "bar ./test" } }
then you could run `npm start` to execute the `bar` script, which is
exported into the `node_modules/.bin` directory on `npm install`.
### package.json vars
The package.json fields are tacked onto the `npm_package_` prefix. So,
for instance, if you had `{"name":"foo", "version":"1.2.5"}` in your
package.json file, then your package scripts would have the
`npm_package_name` environment variable set to "foo", and the
`npm_package_version` set to "1.2.5"
### configuration
Configuration parameters are put in the environment with the
`npm_config_` prefix. For instance, you can view the effective `root`
config by checking the `npm_config_root` environment variable.
### Special: package.json "config" object
The package.json "config" keys are overwritten in the environment if
there is a config param of `<name>[@<version>]:<key>`. For example,
if the package.json has this:
{ "name" : "foo"
, "config" : { "port" : "8080" }
, "scripts" : { "start" : "node server.js" } }
and the server.js is this:
http.createServer(...).listen(process.env.npm_package_config_port)
then the user could change the behavior by doing:
npm config set foo:port 80
### current lifecycle event
Lastly, the `npm_lifecycle_event` environment variable is set to
whichever stage of the cycle is being executed. So, you could have a
single script used for different parts of the process which switches
based on what's currently happening.
Objects are flattened following this format, so if you had
`{"scripts":{"install":"foo.js"}}` in your package.json, then you'd
see this in the script:
process.env.npm_package_scripts_install === "foo.js"
## EXAMPLES
For example, if your package.json contains this:
{ "scripts" :
{ "install" : "scripts/install.js"
, "postinstall" : "scripts/install.js"
, "uninstall" : "scripts/uninstall.js"
}
}
then `scripts/install.js` will be called for the install
and post-install stages of the lifecycle, and `scripts/uninstall.js`
will be called when the package is uninstalled. Since
`scripts/install.js` is running for two different phases, it would
be wise in this case to look at the `npm_lifecycle_event` environment
variable.
If you want to run a make command, you can do so. This works just
fine:
{ "scripts" :
{ "preinstall" : "./configure"
, "install" : "make && make install"
, "test" : "make test"
}
}
## EXITING
Scripts are run by passing the line as a script argument to `sh`.
If the script exits with a code other than 0, then this will abort the
process.
Note that these script files don't have to be nodejs or even
javascript programs. They just have to be some kind of executable
file.
## HOOK SCRIPTS
If you want to run a specific script at a specific lifecycle event for
ALL packages, then you can use a hook script.
Place an executable file at `node_modules/.hooks/{eventname}`, and
it'll get run for all packages when they are going through that point
in the package lifecycle for any packages installed in that root.
Hook scripts are run exactly the same way as package.json scripts.
That is, they are in a separate child process, with the env described
above.
## BEST PRACTICES
* Don't exit with a non-zero error code unless you *really* mean it.
Except for uninstall scripts, this will cause the npm action to
fail, and potentially be rolled back. If the failure is minor or
only will prevent some optional features, then it's better to just
print a warning and exit successfully.
* Try not to use scripts to do what npm can do for you. Read through
`package.json(5)` to see all the things that you can specify and enable
by simply describing your package appropriately. In general, this
will lead to a more robust and consistent state.
* Inspect the env to determine where to put things. For instance, if
the `npm_config_binroot` environment variable is set to `/home/user/bin`, then
don't try to install executables into `/usr/local/bin`. The user
probably set it up that way for a reason.
* Don't prefix your script commands with "sudo". If root permissions
are required for some reason, then it'll fail with that error, and
the user will sudo the npm command in question.
* Don't use `install`. Use a `.gyp` file for compilation, and `prepublish`
for anything else. You should almost never have to explicitly set a
preinstall or install script. If you are doing this, please consider if
there is another option. The only valid use of `install` or `preinstall`
scripts is for compilation which must be done on the target architecture.
## SEE ALSO
* npm-run-script(1)
* package.json(5)
* npm-developers(7)
* npm-install(1)
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