Using File Watchers
File Watcher is a built-in PyCharm tool that allows you to automatically run a command-line tool like compilers, formatters, or linters when you change or save a file in the IDE.
You can configure a File Watcher from scratch or use one of the available templates. Configured File Watcher can be saved in your project settings or in the IDE settings and used in different projects.
Creating a File Watcher
Create a File Watcher
In the Settings/Preferences dialog (Ctrl+Alt+S), click File Watchers under Tools. The File Watchers page opens showing a list of File Watchers that are already configured in this project and in the IDE.
Click and choose the predefined template from which you want to create a File Watcher. The choice depends on the tool you are going to use. To use a tool that is not on the list, choose Custom. The New Watcher dialog box opens.
In the Name text box, type the name of the File Watcher. By default, PyCharm suggests the name of the selected predefined template.
Configuring the expected type and location of input files
Use the controls in the Files to watch area to define the range of files where you want to apply the File Watcher.
From the File type drop-down list, choose the expected type of input files. The File Watcher will consider only files of this type as subject for analyzing and processing. File types are recognised based on associations between file types and file extensions.
- Choose the Scope in which the File Watcher is applicable. Changes in these files will invoke the File Watcher either immediately or upon save or frame deactivation, depending on the status of the Auto-save edited files to trigger the watcher checkbox.
Choose one of the predefined scopes from the drop-down list. For a project-level File Watcher, you can also click to configure a custom scope in the Scopes dialog that opens.
- Optionally: specify how you want the File Watcher to deal with dependencies. A root file is a file that is not included (e.g. via
import) in any other file within the specified scope.
To run the File Watcher only against root files, select the Track only root files checkbox.
Clear the checkbox to run the File Watcher against the file from which it is invoked and against all the files in which this file is recursively included within the specified scope.
Configuring interaction with the external tool
In the Tool to run on changes area, specify the tool to use, the arguments to pass to it, the expected output file types, etc.
- In the Program text box, specify the path to the executable file of the tool (
.bat, or other depending on the specific tool).
If you are configuring a global file watcher for a tool installed inside a project (e.g. Prettier), you need to specify the path to it using a macro. To use one of the available macros in the path, press the Insert Macro button. For example, with the path $ProjectFileDir$/node_modules/.bin/prettier, the File Watcher will use prettier installed in the project’s node_module folder.
In the Arguments text box, define the arguments to pass to the tool. Arguments are usually specified using macros, for example,
$FileNameWithoutExtension$, that will be replaced with actual file names.
Type the macros manually or click Insert Macro and select the relevant pattern fom the list in the Macros dialog that opens.
- In the Output paths to refresh text box, specify the files where the tool stores its output: the resulting source code, source maps, and dependencies. Based on these settings, PyCharm recognizes the files generated through compilation.
Please note, that changing the value in the Output paths to refresh text box does not make the tool store its output in another place. If you still need to do that, specify the desired custom output location in the Arguments text box: type the output paths with colons as separators and use macros.
Output paths are usually specified using macros. Type the path manually o click Insert Macro and select the relevant pattern from the list.
Expand the Working Directory and Environment Variables hidden area.
Define the environment variables. For example, specify the
PATHvariable for the tools that are required for starting the tool you are configuring but are not referenced in the path to it. In most cases it is Node.js or ruby.exe. Such situation may result from custom manual installation instead of installation through the Node Package Manager (npm) or gem manager.
In the Working Directory text box, specify the directory to which the tool will be applied.
Because the tool is always invoked in the context of a file, the default working directory is the directory of the current file. The default working directory is specified in all predefined templates through a
$FileDir$macros. To specify a custom working directory, type the path to it in the text box, or click and choose the directory in the Select Path dialog box, or click Insert Macro and select the desired macro from the list in the Macros dialog box.
Configuring advanced options
In the Advanced Options area, customize the default behaviour of the File Watcher.
- Specify the events that will invoke the File Watcher:
To invoke the File Watcher as soon as any changes are made to the source code, select the Auto-save edited files to trigger the watcher checkbox.
When the checkbox is cleared, the File Watcher starts upon save ( ) or when you move the focus from PyCharm (on frame deactivation).
By default, the File Watcher wakes up on any saved change, including the updates received from you version control system when you, for example, check out a branch. To ignore such changes and invoke the File Watcher only you update your code in PyCharm, clear the Trigger the watcher on external changes checkbox.
- Specify whether you want the File Watcher to interact with the PyCharm syntax parser:
When the Trigger watcher regardless of syntax errors checkbox is selected, the File Watcher start regardless of the syntactical correctness of a file. The File Watcher will start upon update, save, or frame deactivation, depending on the status of the Auto-save edited files to trigger the watcher checkbox.
When the Trigger watcher regardless of syntax errors checkbox is cleared, the File Watcher ignores all triggers in files that are syntactically invalid and starts only in error-free files.
- Use the Create output file from stdout checkbox to specify how you want to generate the output file.
When the checkbox is selected, PyCharm reads the native tool's output (
standard output stream (stdout)) and generates the resulting files from it.
When the checkbox is cleared, the tool writes its output directly to the files specified in the Output paths to refresh field.
- In the Show console drop-down list, choose when you want the File Watcher to open the console.
Always: with this option, the console always opens after the tool execution is completed.
On error: with this option, the console opens after the tool execution only when the
Exit codeis different from
Never: choose this option to suppress opening the console at all.
Showing information reported by File Watcher in the editor
If the tool configured in the File Watcher reports errors or warnings about your code with the links to the files and specific lines, you can see this information right in the editor:
In File Watcher Problems., enable the inspection
In the Output Filters field of the Edit Watcher dialog, describe the format of the output you want to match. Use the macros
$MESSAGE$for that. You need to avoid using special symbols like braces and dot with
\. The text matched with the
$MESSAGE$macro will be shown in the editor.
The tool reports errors in the following format:
ERROR: /Users/Alice/WebstormProjects/angular-app/src/main.ts[6, 27]: " should be '
ERROR: $FILE_PATH$\[$LINE$, $COLUMN$\]: $MESSAGE$
Saving, enabling and disabling File Watchers
Once you’ve saved the new File Watcher, you can decide if it’s going to be available only in the current project (select Project in the right column) or for all projects (select Global).
To enable or disable a File Watcher, select or clear the checkbox next to it indialog.
To toggle the enable/disable status of a File Watcher, select/clear the checkbox next to it on the File Watchers page of the Settings dialog box. If an error occurs while a File Watcher is running, the File Watcher is automatically disabled. To restore the status, enable the File Watcher manually.
When a File Watcher is enabled, it starts automatically as soon as a file of the selected type and in the selected scope is changed or saved, see Configuring advanced options.
Examples of customizing the behaviour of an external tool in a File Watcher
The only way to influence a third-party tool is to pass arguments to it just as if you were working in the command line mode. These arguments are specific to each tool. Below are two examples of customizing the default output location for the CoffeeScript compiler.
Suppose, you have a project with the following folder structure: By default, the generated files will be stored in the folder where the original file is. You can change this default location and have the generated files stored in the
js folder. Moreover, you can have them stored in a flat list or arranged in the folder structure that repeats the original structure under the
To store all the generated files in the output js folder
In the Arguments text box, type:
--output $ProjectFileDir$\js\$FileDirRelativeToProjectRoot$\ --compile --map $FileName$
In the Output paths to refresh text box, type:As a result, the project tree looks as follows:
Troubleshooting File Watchers
There might be a red error message next to the File Watcher in the list in.
Here is a list of possible errors:
The File Watcher uses a scope that is not defined in this project.
Double-click on the watcher and select an available scope or create a new one.
The project uses a global File Watcher that was removed.
Delete the watcher from the list using the Remove button () or edit it to create a new global watcher with the same name.