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+npm-folders(1) -- Folder Structures Used by npm
+===============================================
+
+## DESCRIPTION
+
+npm puts various things on your computer. That's its job.
+
+This document will tell you what it puts where.
+
+### tl;dr
+
+* Local install (default): puts stuff in `./node_modules` of the current
+ package root.
+* Global install (with `-g`): puts stuff in /usr/local or wherever node
+ is installed.
+* Install it **locally** if you're going to `require()` it.
+* Install it **globally** if you're going to run it on the command line.
+* If you need both, then install it in both places, or use `npm link`.
+
+### prefix Configuration
+
+The `prefix` config defaults to the location where node is installed.
+On most systems, this is `/usr/local`, and most of the time is the same
+as node's `process.installPrefix`.
+
+On windows, this is the exact location of the node.exe binary. On Unix
+systems, it's one level up, since node is typically installed at
+`{prefix}/bin/node` rather than `{prefix}/node.exe`.
+
+When the `global` flag is set, npm installs things into this prefix.
+When it is not set, it uses the root of the current package, or the
+current working directory if not in a package already.
+
+### Node Modules
+
+Packages are dropped into the `node_modules` folder under the `prefix`.
+When installing locally, this means that you can
+`require("packagename")` to load its main module, or
+`require("packagename/lib/path/to/sub/module")` to load other modules.
+
+Global installs on Unix systems go to `{prefix}/lib/node_modules`.
+Global installs on Windows go to `{prefix}/node_modules` (that is, no
+`lib` folder.)
+
+If you wish to `require()` a package, then install it locally.
+
+### Executables
+
+When in global mode, executables are linked into `{prefix}/bin` on Unix,
+or directly into `{prefix}` on Windows.
+
+When in local mode, executables are linked into
+`./node_modules/.bin` so that they can be made available to scripts run
+through npm. (For example, so that a test runner will be in the path
+when you run `npm test`.)
+
+### Man Pages
+
+When in global mode, man pages are linked into `{prefix}/share/man`.
+
+When in local mode, man pages are not installed.
+
+Man pages are not installed on Windows systems.
+
+### Cache
+
+See `npm-cache(1)`. Cache files are stored in `~/.npm` on Posix, or
+`~/npm-cache` on Windows.
+
+This is controlled by the `cache` configuration param.
+
+### Temp Files
+
+Temporary files are stored by default in the folder specified by the
+`tmp` config, which defaults to the TMPDIR, TMP, or TEMP environment
+variables, or `/tmp` on Unix and `c:\windows\temp` on Windows.
+
+Temp files are given a unique folder under this root for each run of the
+program, and are deleted upon successful exit.
+
+## More Information
+
+When installing locally, npm first tries to find an appropriate
+`prefix` folder. This is so that `npm install foo@1.2.3` will install
+to the sensible root of your package, even if you happen to have `cd`ed
+into some other folder.
+
+Starting at the $PWD, npm will walk up the folder tree checking for a
+folder that contains either a `package.json` file, or a `node_modules`
+folder. If such a thing is found, then that is treated as the effective
+"current directory" for the purpose of running npm commands. (This
+behavior is inspired by and similar to git's .git-folder seeking
+logic when running git commands in a working dir.)
+
+If no package root is found, then the current folder is used.
+
+When you run `npm install foo@1.2.3`, then the package is loaded into
+the cache, and then unpacked into `./node_modules/foo`. Then, any of
+foo's dependencies are similarly unpacked into
+`./node_modules/foo/node_modules/...`.
+
+Any bin files are symlinked to `./node_modules/.bin/`, so that they may
+be found by npm scripts when necessary.
+
+### Global Installation
+
+If the `global` configuration is set to true, then npm will
+install packages "globally".
+
+For global installation, packages are installed roughly the same way,
+but using the folders described above.
+
+### Cycles, Conflicts, and Folder Parsimony
+
+Cycles are handled using the property of node's module system that it
+walks up the directories looking for `node_modules` folders. So, at every
+stage, if a package is already installed in an ancestor `node_modules`
+folder, then it is not installed at the current location.
+
+Consider the case above, where `foo -> bar -> baz`. Imagine if, in
+addition to that, baz depended on bar, so you'd have:
+`foo -> bar -> baz -> bar -> baz ...`. However, since the folder
+structure is: `foo/node_modules/bar/node_modules/baz`, there's no need to
+put another copy of bar into `.../baz/node_modules`, since when it calls
+require("bar"), it will get the copy that is installed in
+`foo/node_modules/bar`.
+
+This shortcut is only used if the exact same
+version would be installed in multiple nested `node_modules` folders. It
+is still possible to have `a/node_modules/b/node_modules/a` if the two
+"a" packages are different versions. However, without repeating the
+exact same package multiple times, an infinite regress will always be
+prevented.
+
+Another optimization can be made by installing dependencies at the
+highest level possible, below the localized "target" folder.
+
+#### Example
+
+Consider this dependency graph:
+
+ foo
+ +-- blerg@1.2.5
+ +-- bar@1.2.3
+ | +-- blerg@1.x (latest=1.3.7)
+ | +-- baz@2.x
+ | | `-- quux@3.x
+ | | `-- bar@1.2.3 (cycle)
+ | `-- asdf@*
+ `-- baz@1.2.3
+ `-- quux@3.x
+ `-- bar
+
+In this case, we might expect a folder structure like this:
+
+ foo
+ +-- node_modules
+ +-- blerg (1.2.5) <---[A]
+ +-- bar (1.2.3) <---[B]
+ | +-- node_modules
+ | | `-- baz (2.0.2) <---[C]
+ | | `-- node_modules
+ | | `-- quux (3.2.0)
+ | `-- asdf (2.3.4)
+ `-- baz (1.2.3) <---[D]
+ `-- node_modules
+ `-- quux (3.2.0) <---[E]
+
+Since foo depends directly on bar@1.2.3 and baz@1.2.3, those are
+installed in foo's `node_modules` folder.
+
+Even though the latest copy of blerg is 1.3.7, foo has a specific
+dependency on version 1.2.5. So, that gets installed at [A]. Since the
+parent installation of blerg satisfie's bar's dependency on blerg@1.x,
+it does not install another copy under [B].
+
+Bar [B] also has dependencies on baz and asdf, so those are installed in
+bar's `node_modules` folder. Because it depends on `baz@2.x`, it cannot
+re-use the `baz@1.2.3` installed in the parent `node_modules` folder [D],
+and must install its own copy [C].
+
+Underneath bar, the `baz->quux->bar` dependency creates a cycle.
+However, because `bar` is already in `quux`'s ancestry [B], it does not
+unpack another copy of bar into that folder.
+
+Underneath `foo->baz` [D], quux's [E] folder tree is empty, because its
+dependency on bar is satisfied by the parent folder copy installed at [B].
+
+For a graphical breakdown of what is installed where, use `npm ls`.
+
+### Publishing
+
+Upon publishing, npm will look in the `node_modules` folder. If any of
+the items there are not in the `bundledDependencies` array, then they will
+not be included in the package tarball.
+
+This allows a package maintainer to install all of their dependencies
+(and dev dependencies) locally, but only re-publish those items that
+cannot be found elsewhere. See `npm-json(1)` for more information.
+
+## SEE ALSO
+
+* npm-faq(1)
+* npm-json(1)
+* npm-install(1)
+* npm-pack(1)
+* npm-cache(1)
+* npm-config(1)
+* npm-publish(1)

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