Watchman file queries consist of 1 or more generators that feed files through the expression evaluator.

Generators

Generators are analogous to the list of paths that you specify when using the find(1) utility, but are implemented in watchman with a bit of a twist because watchman doesn’t need to crawl the filesystem in realtime and instead maintains a couple of indexes over the tree.

A query may specify any number of generators; each generator will emit its list of files and this may mean that you see the same file output more than once if you specified the use of multiple generators that all produce the same file.

Watchman provides 5 generators:

  • since: produces a list of files that were modified since a specific clockspec.
  • suffix: produces a list of files that have a particular suffix.
  • glob: efficiently pattern match a list of files based on their names.
  • path: produces a list of files based on their path and depth.
  • all: produces a list of all known files

De-duplicating results

Since 4.7.

If your query uses multiple generators, or configures the path generator with paths that yield multiple results, the default behavior (for backwards compatibility reasons) is to emit those duplicate results in the query output.

You may ask Watchman to de-duplicate results for you by enabling the dedup_results boolean in your query:

$ watchman -j <<-EOT
["query", "/path/to/root", {
  "path": ["bar", "bar"],
  "dedup_results": true
}]
EOT

You may test for this feature using an extended version command and requesting the capability name dedup_results.

Since Generator

The since generator produces a list of files that were modified since a specific clockspec.

The following query will consider the set of files changed since the last query using the named cursor mycursor and then pass them to the expression evaluator to be filtered to just those that are files:

$ watchman -j <<-EOT
["query", "/path/to/root", {
  "since": "n:mycursor",
  "expression": ["type", "f"]
}]
EOT

If the since parameter value is blank, was produced by a different watchman process (in other words, the watchman process was restarted between the time that the value was obtained and the time the query was issued) or is a named cursor that has not yet been used in a query, the since generator will consider the state to be a fresh instance and its behavior is modified:

A fresh instance result set will only include files that currently exist and will generate file nodes that are always considered to be new.

If the query was configured with the empty_on_fresh_instance property set to true then the result set will be empty and the is_fresh_instance property will be set to true in the result object.

The since generator also knows how to talk to source control; you can read more about that here.

The since generator does not consider the targets of symlinks. In particular, the since generator may not produce a symlink in the following cases:

  • The symlink’s target was a file, and the file is since modified.
  • The symlink’s target was a file, and the file is since deleted or replaced with a different file.
  • An ancestor of the symlink’s target was created or deleted or modified.
  • The symlink’s target was a directory, and a file is since added or removed from that directory.

Suffix Generator

The suffix generator produces a list of files that have a particular suffix or set of suffixes. The value can be either a string or an array of strings.

$ watchman -j <<-EOT
["query", "/path/to/root", {
  "suffix": "js"
}]
EOT
$ watchman -j <<-EOT
["query", "/path/to/root", {
  "suffix": ["js", "css"]
}]
EOT

If the suffix generator is given an empty array, it produces no files.

The suffix generator can produce symlinks.

The suffix generator does not follow symlinks. For example, a symlink to /etc will not cause a "suffix": "conf" query to search within /etc and produce /etc/resolv.conf.

Glob Generator

Since 4.7.

The glob generator produces a list of files by matching against your input list of patterns. It does this by building a tree from the glob expression(s) and walking both the expression and the in-memory filesystem tree concurrently.

This query will yield a list of all of the C source and header files found directly in the src dir:

$ watchman -j <<-EOT
["query", "/path/to/root", {
  "glob": ["src/*.c", "src/*.h"],
  "fields": ["name"]
}]

This query will yield a list of all of the C source and header files found in any subdirectories of the root:

$ watchman -j <<-EOT
["query", "/path/to/root", {
  "glob": ["**/*.c", "**/*.h"],
  "fields": ["name"]
}]

Note that it is more efficient to use the suffix generator together with a dirname expression term for such a broadly scoped query as it results in fewer comparisons. This example is included as an illustration of recursive globbing.

The glob generator implicitly enables dedup_results mode.

If the glob generator is given an empty array, it produces no files.

The glob generator can produce symlinks.

The glob generator does not follow symlinks. For example, a symlink to /etc will not cause a "glob": ["**/resolv.conf"] query to search within /etc and produce /etc/resolv.conf.

Path Generator

The path generator produces a list of files based on their path and depth. Depth controls how far watchman will search down the directory tree for files.

The path generator expects an array of path specifiers. Each path specifier can be either a string or an object and each will produce a set of files.

If it is a string then it is treated as the value for path with depth set to infinite. If an object, the fields path (a string) and depth (an integer) must be supplied.

Paths are relative to the root, so if watchman is watching /foo/, path bar refers to /foo/bar.

A depth value of 0 means only files and directories which are contained in this path. A depth value of -1 means no limit on the depth.

The following path generators are equivalent:

$ watchman -j <<-EOT
["query", "/path/to/root", {
  "path": ["bar"]
}]
EOT
$ watchman -j <<-EOT
["query", "/path/to/root", {
  "path": [{"path": "bar", "depth": -1}]
}]
EOT

If the path generator is given an empty array, it produces no files.

The path generator can produce symlinks.

The path generator does not follow symlinks.

All Generator

The all generator produces a list of all file nodes. It is the default generator and is used in the case where no other generators were explicitly specified.

$ watchman -j <<-EOT
["query", "/path/to/root", {
}]
EOT

The all generator can produce symlinks.

The all generator does not follow symlinks.

Expressions

A watchman query expression consists of 0 or more expression terms. If no terms are provided then each file evaluated is considered a match (equivalent to specifying a single true expression term).

Otherwise, the expression is evaluated against the file and produces a boolean result. If that result is true then the file is considered a match and is added to the output set.

An expression term is canonically represented as a JSON array whose zeroth element is a string containing the term name.

["termname", arg1, arg2]

If the term accepts no arguments you may use a short form that consists of just the term name expressed as a string:

"true"

Expressions that match against file names may match against either the basename or the wholename of the file. The basename is the name of the file within its containing directory. The wholename is the name of the file relative to the watched root.

You can find a list of all possible expression terms in the sidebar on the left of this page.

Relative roots

Since 3.3.

Watchman supports optionally evaluating queries with respect to a path within a watched root. This is used with the relative_root parameter:

["query", "/path/to/watched/root", {
  "relative_root": "project1",
}]

Setting a relative root results in the following modifications to queries:

  • The path generator is evaluated with respect to the relative root. In the above example, "path": ["dir"] will return all files inside /path/to/watched/root/project1/dir.
  • The input expression is evaluated with respect to the relative root. In the above example, "expression": ["match", "dir/*.txt", "wholename"] will return all files inside /path/to/watched/root/project1/dir/ that match the glob *.txt.
  • Paths inside the relative root are returned with the relative root stripped off. For example, a path project1/dir/file.txt would be returned as dir/file.txt.
  • Paths outside the relative root are not returned.

Relative roots behave similarly to a separate Watchman watch on the subdirectory, without any of the system overhead that that imposes. This is useful for large repositories, where your script or tool is only interested in a particular directory inside the repository.