GNOME JavaScript

File Operations

The best way to operate on files in GJS is with Gio.Fileopen in new window, which is an abstraction of a file that can be treated like an object.

In contrast to the low-level functions available in GLib, Gio.File supports asynchronous operations and many utility functions for creating, reading, writing and querying information.

Getting a File Object

Before you can create, read or write a file you need to create a Gio.File object to operate on. Below is a simple example of create a Gio.File instance for a file path:

const {Gio, GLib} = imports.gi;

// This is a useful method for building file paths from GLib. It will use the
// correct path separator for the current operating system (eg. `/` or `\`)
const filepath = GLib.build_filenamev([GLib.get_home_dir(), 'test-file.txt']);

const file = Gio.File.new_for_path(filepath);
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You can also create a Gio.File instance from a URI, such as file:// URIs. Note that while this function will never fail to return a Gio.File object for a well-formed URI, operations on the file will only succeed if the URI type is supported.

const {Gio} = imports.gi;

const file = Gio.File.new_for_uri('file:///home/username/test-file.txt');
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Creating Files and Folders

A Gio.File object is only a representation of a file. To create a regular file on disk, you can use Gio.File.create()open in new window:

const {GLib, Gio} = imports.gi;

const file = Gio.File.new_for_path('test-file.txt');

// Synchronous, blocking method
const outputStream = file.create(Gio.FileCreateFlags.NONE, null);

// Asynchronous, non-blocking method
const outputStream = await new Promise((resolve, reject) => {
    file.create_async(
        Gio.FileCreateFlags.NONE,
        GLib.PRIORITY_DEFAULT,
        null,
        (file_, result) => {
            try {
                resolve(file.create_finish(result));
            } catch (e) {
                reject(e);
            }
        }
    );
});
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If the file already exists, then Gio.File.create() will throw an error. If you want to replace an existing file, use Gio.File.replace()open in new window instead and pass Gio.FileCreateFlags.REPLACE_DESTINATION in the flags argument.

Both Gio.File.create() and Gio.File.replace() open the file in write mode and return a Gio.FileOutputStreamopen in new window so that you can follow these calls by writing to the stream:

const bytesWritten = await new Promise((resolve, reject) => {
    outputStream.write_bytes_async(
        new GLib.Bytes('some file content'),
        GLib.PRIORITY_DEFAULT,
        null,
        (stream_, result) => {
            try {
                resolve(outputStream.write_bytes_finish(result));
            } catch (e) {
                reject(e);
            }
        }
    );
});
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To create a directory instead, you can use Gio.File.make_directory()open in new window:

const {GLib, Gio} = imports.gi;

const file = Gio.File.new_for_path('test-directory');

// Synchronous, blocking method
file.make_directory(null);

// Asynchronous, non-blocking method
await new Promise((resolve, reject) => {
    file.make_directory_async(
        GLib.PRIORITY_DEFAULT,
        null,
        (file_, result) => {
            try {
                resolve(file.make_directory_finish(result));
            } catch (e) {
                reject(e);
            }
        }
    );
});
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Note that this function will not make directories recursively, so you must use Gio.File.make_directory_with_parents()open in new window if you do want to do this manually:

const {GLib, Gio} = imports.gi;

const file = Gio.File.new_for_path('test-directory');
const child = file.get_child('test-subdirectory');

// Synchronous, blocking method
child.make_directory_with_parents(null);
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Unfortunately, there is no asynchronous version of this method in GIO.

Simple Reading and Writing

For simple operations like loading the contents of a file or writing contents out to file, you probably don't want to bother with I/O streams.

Reading File Contents

To read the contents of a file, you can use Gio.File.load_contents()open in new window:

const {GLib, Gio} = imports.gi;

const file = Gio.File.new_for_path('test-file.txt');

// Synchronous, blocking method
const [, contents, etag] = file.load_contents(null);

// Asynchronous, non-blocking method
const [, contents, etag] = await new Promise((resolve, reject) => {
    file.load_contents_async(
        null,
        (file_, result) => {
            try {
                resolve(file.load_contents_finish(result));
            } catch (e) {
                reject(e);
            }
        }
    );
});
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The result of this operation will be a Uint8Arrayopen in new window. To convert this to a string, you can use TextDecoder()open in new window or ByteArray.toString():

// GJS >= 1.70 (GNOME 41)
const decoder = new TextDecoder('utf-8');
const contentsString = decoder.decode(contents);

// GJS < 1.70 (GNOME 40 or older)
const ByteArray = imports.byteArray;
const contentsString = ByteArray.toString(contents);
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Writing File Contents

To write contents to a file, you can use Gio.File.replace_contents()open in new window

Note that when writing contents asynchronously, it is strongly advised that you use Gio.File.replace_contents_bytes_async()open in new window. Not doing so may lead to file corruption if you are not very careful with the lifetime of the data.

const {GLib, Gio} = imports.gi;

const file = Gio.File.new_for_path('test-file.txt');

// Synchronous, blocking method
const [, etag] = file.replace_contents('some file contents', null, false,
    Gio.FileCreateFlags.REPLACE_DESTINATION, null);

// Asynchronous, non-blocking method
const [, etag] = await new Promise((resolve, reject) => {
    file.replace_contents_bytes_async(
        new GLib.Bytes('some file contents'),
        null,
        false,
        Gio.FileCreateFlags.REPLACE_DESTINATION,
        null,
        (file_, result) => {
            try {
                resolve(file.replace_contents_finish(result));
            } catch (e) {
                reject(e);
            }
        }
    );
});
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Opening File Streams

When you want to perform more complicated operations on files or pipe the data to or from another source, you can open IO streams for a file instead.

For example, to open file in read-only mode you can use Gio.File.read()open in new window:

const {Gio, GLib} = imports.gi;

const file = Gio.File.new_for_path('test-file.txt');

// Synchronous, blocking method
const inputStream = file.read(null);

// Asynchronous, non-blocking method
const inputStream = await new Promise((resolve, reject) => {
    file.read_async(
        GLib.PRIORITY_DEFAULT,
        null,
        (file_, result) => {
            try {
                resolve(file.read_finish(result));
            } catch (e) {
                reject(e);
            }
        }
    );
});
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This will return a Gio.FileInputStreamopen in new window so that you can follow this call by reading from the stream:

const contentsBytes = await new Promise((resolve, reject) => {
    inputStream.read_bytes_async(
        4096,
        GLib.PRIORITY_DEFAULT,
        null,
        (stream_, result) => {
            try {
                resolve(inputStream.read_bytes_finish(result));
            } catch (e) {
                reject(e);
            }
        }
    );
});
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To open file in read-write mode instead, you can use Gio.File.open_readwrite()open in new window:

const {GLib, Gio} = imports.gi;

const file = Gio.File.new_for_path('test-file.txt');

// Synchronous, blocking method
const ioStream = file.open_readwrite(null);

// Asynchronous, non-blocking method
const ioStream = await new Promise((resolve, reject) => {
    file.open_readwrite_async(
        GLib.PRIORITY_DEFAULT,
        null,
        (file_, result) => {
            try {
                resolve(file.open_readwrite_finish(result));
            } catch (e) {
                reject(e);
            }
        }
    );
});
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This will return a Gio.FileIOStreamopen in new window, which holds both an Gio.FileInputStream you can use for reading and a Gio.FileOutputStream you can use for writing:

const inputStream = ioStream.get_input_stream();
const outputStream = ioStream.get_output_stream();
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There are several other comparable methods you can use, depending on what operations you want to perform. See the documentation for the following methods for details:

Copying and Moving Files

To copy files from one location to another, you will need a Gio.File object for both the source and target locations. Once you have those, you can use Gio.File.copy()open in new window to copy the file.

Be sure to review the Gio.FileCopyFlagsopen in new window documentation, to select the correct flags for the operation you want to perform.

Note that Gio.File.copy() will not copy non-empty directories, nor will it recursively copy files. To do that you must recursively copy files manually.

const {Gio, GLib} = imports.gi;

const source = Gio.File.new_for_path('test-file.txt');
const target = Gio.File.new_for_path('test-copy.txt');

// Synchronous, blocking method
source.copy(target, Gio.FileCopyFlags.NONE, null, null);

// Asynchronous, non-blocking method
await new Promise((resolve, reject) => {
    source.copy_async(
        target,
        Gio.FileCopyFlags.NONE,
        GLib.PRIORITY_DEFAULT,
        null,
        (file_, result) => {
            try {
                resolve(file.copy_finish(result));
            } catch (e) {
                reject(e);
            }
        }
    );
});
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If you want to move a file instead of copying it, you can use Gio.File.move()open in new window. Unlike Gio.File.copy(), this function can move entire directories of files.

const {Gio, GLib} = imports.gi;

const source = Gio.File.new_for_path('test-file.txt');
const target = Gio.File.new_for_path('test-move.txt');

// Synchronous, blocking method
source.move(target, Gio.FileCopyFlags.NONE, null, null);

// Asynchronous, non-blocking method
await new Promise((resolve, reject) => {
    source.copy_async(
        target,
        Gio.FileCopyFlags.NONE,
        GLib.PRIORITY_DEFAULT,
        null,
        (file_, result) => {
            try {
                resolve(file.move_finish(result));
            } catch (e) {
                reject(e);
            }
        }
    );
});
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Deleting Files

To delete files, you can use Gio.File.delete()open in new window:

const {GLib, Gio} = imports.gi;

const file = Gio.File.new_for_path('test-file.txt');

// Synchronous, blocking method
file.delete(null);

// Asynchronous, non-blocking method
await new Promise((resolve, reject) => {
    file.delete_async(
        GLib.PRIORITY_DEFAULT,
        null,
        (file_, result) => {
            try {
                resolve(file.delete_finish(result));
            } catch (e) {
                reject(e);
            }
        }
    );
});
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Note that Gio.File.delete() will not delete non-empty directories, nor will it recursively delete files. To do that you must recursively delete files manually.

You may, however, use Gio.File.trash()open in new window to send entire directories of files to the user's Trash:

const {GLib, Gio} = imports.gi;

const file = Gio.File.new_for_path('test-file.txt');

// Synchronous, blocking method
file.trash(null);

// Asynchronous, non-blocking method
await new Promise((resolve, reject) => {
    file.trash_async(
        GLib.PRIORITY_DEFAULT,
        null,
        (file_, result) => {
            try {
                resolve(file.trash_finish(result));
            } catch (e) {
                reject(e);
            }
        }
    );
});
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Getting File Information

To query file information, you can use Gio.File.query_info()open in new window which will return a Gio.FileInfoopen in new window. Depending on the attributes you request, the returned Gio.FileInfo object can be used to retrieve different information about the file.

In the example below, all the standard attributes are pulled in by passing the string standard::*. This could also be a list of specific namespaces and attributes like standard::name,standard::type,unix::uid, but usually everything you need will be included in standard::*.

You will also notice the flag Gio.FileQueryInfoFlags.NOFOLLOW_SYMLINKS, which indicates that if the Gio.File object represents a symbolic link that the info for the link itself is being requested, not the file it points to.

const {GLib, Gio} = imports.gi;

const file = Gio.File.new_for_path('test-file.txt');

// Synchronous, blocking method
const info = file.query_info('standard::*',
    Gio.FileQueryInfoFlags.NOFOLLOW_SYMLINKS, null);

// Asynchronous, non-blocking method
const info = await new Promise((resolve, reject) => {
    file.query_info_async(
        'standard::*',
        Gio.FileQueryInfoFlags.NOFOLLOW_SYMLINKS,
        GLib.PRIORITY_DEFAULT,
        (file_, result) => {
            try {
                resolve(file.query_info_finish(result));
            } catch (e) {
                reject(e);
            }
        }
    );
});
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For attributes in the standard namespace there are convenience methods like Gio.FileInfo.get_size()open in new window, but others require methods like Gio.FileInfo.get_attribute_uint32()open in new window:

// Attributes in the `standard` namespace
const fileName = info.get_name();
const fileSize = info.get_size();

// Attributes in other namespaces
const unixMode = info.get_attribute_uint32('unix::uid');
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Navigating files and directories is quite simple, if you already know what you're looking for. The Gio.File.get_child()open in new window and Gio.File.get_parent()open in new window methods take a string and return a Gio.File object for that path:

const {Gio, GLib} = imports.gi;

// Our starting point, in the current working directory
const cwd = Gio.File.new_for_path('.');

// A child of the directory
const childFile = cwd.get_child('test-file.txt');

// The parent directory
const parentDir = cwd.get_parent();

// A child of the parent directory
const parentFile = parentDir.get_child('parent-file.txt');
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If you don't know the files you're looking for, you can instead list the files and iterate them with Gio.File.enumerate_children()open in new window. This method will return a Gio.FileEnumeratoropen in new window that you can call Gio.FileEnumerator.next_file()open in new window on to retrieve a Gio.FileInfo object for each file:

const {Gio, GLib} = imports.gi;

const directory = Gio.File.new_for_path('.');

// Synchronous, blocking method
const iter = directory.enumerate_children('standard::*',
    Gio.FileQueryInfoFlags.NOFOLLOW_SYMLINKS, null);

while (true) {
    const info = iter.next_file(null);
    
    if (info == null)
        break;
        
    log(info.get_name()); 
}

// Asynchronous, non-blocking method
const iter = await new Promise((resolve, reject) => {
    directory.enumerate_children_async(
        'standard::*',
        Gio.FileQueryInfoFlags.NOFOLLOW_SYMLINKS,
        GLib.PRIORITY_DEFAULT,
        cancellable,
        (file_, result) => {
            try {
                resolve(directory.enumerate_children_finish(result));
            } catch (e) {
                reject(e);
            }
        }
    );
});

while (true) {
    const infos = await new Promise((resolve, reject) => {
        iter.next_files_async(
            10, // max results
            GLib.PRIORITY_DEFAULT,
            null,
            (iter_, res) => {
                try {
                    resolve(iter.next_files_finish(res));
                } catch (e) {
                    reject(e);
                }
            }
        );
    });

    if (infos.length === 0)
        break;
        
    for (const info of infos)
        log(info.get_name());
}
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Monitoring Files and Directories

It is possible to monitor files and directories for changes with Gio.File. You can use Gio.File.monitor()open in new window to monitor a file or directory for changes.

Be sure to review the Gio.FileMonitorFlagsopen in new window documentation, to select the correct flags for the operations you want to monitor.

const {Gio, GLib} = imports.gi;

const directory = Gio.File.new_for_path('.');

const fileMonitor = file.monitor(Gio.FileMonitorFlags.WATCH_MOVES, null);

fileMonitor.connect('changed', (file, otherFile, eventType) => {
    switch (eventType) {
        case Gio.FileMonitorEvent.CHANGED:
            log(`${otherFile.get_basename()} was changed`);
            break;
            
        case Gio.FileMonitorEvent.DELETED:
            log(`${otherFile.get_basename()} was deleted`);
            break;
            
        case Gio.FileMonitorEvent.CREATED:
            log(`${otherFile.get_basename()} was created`);
            break;
            
        case Gio.FileMonitorEvent.MOVED_IN:
            log(`${otherFile.get_basename()} was moved into the directory`);
            break;
            
        case Gio.FileMonitorEvent.MOVED_OUT:
            log(`${otherFile.get_basename()} was moved out of the directory`);
            break;
    }
});
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Note that you must hold a reference to the returned Gio.FileMonitoropen in new window object.

Complex Examples

A few more complex examples may be useful, to show how Gio.File can be used to solve large or complicated problems without blocking the main thread.

Recursively Deleting a Directory

Although Gio.File.trash() may be used to send non-empty directories to the Trash, deleting an entire directory of files is still a pretty common task.

It is also useful way to demonstrate how to walk a tree of files and call a function on each file based on its type.

const {GLib, Gio} = imports.gi;


// Note that we could inline this function, but we will make it discrete to show
// how you can recursively call any function on files and folders.
function deleteFile(file, cancellable = null) {
    return new Promise((resolve, reject) => {
        file.delete_async(
            GLib.PRIORITY_DEFAULT,
            cancellable,
            (_file, res) => {
                try {
                    resolve(file.delete_finish(res));
                } catch (e) {
                    reject(e);
                }
            }
        );
    });
}

/**
 * Recursively delete @file and any children it may have.
 *
 * @param {Gio.File} file - the file or directory to delete
 * @param {Gio.Cancellable} [cancellable] - optional cancellable
 * @return {Promise} a Promise for the operation
 */
async function deleteDirectory(file, cancellable = null) {
    try {
        const iter = await new Promise((resolve, reject) => {
            file.enumerate_children_async(
                'standard::type',
                Gio.FileQueryInfoFlags.NOFOLLOW_SYMLINKS,
                GLib.PRIORITY_DEFAULT,
                cancellable,
                (_file, res) => {
                    try {
                        resolve(_file.enumerate_children_finish(res));
                    } catch (e) {
                        reject(e);
                    }
                }
            );
        });

        // We'll collect all the branches and operate on them in parallel
        const branches = [];

        while (true) {
            const infos = await new Promise((resolve, reject) => {
                iter.next_files_async(
                    10, // max files
                    GLib.PRIORITY_DEFAULT,
                    cancellable,
                    (_iter, res) => {
                        try {
                            resolve(_iter.next_files_finish(res));
                        } catch (e) {
                            reject(e);
                        }
                    }
                );
            });

            // If none are returned, we're done here
            if (infos.length === 0)
                break;

            // The type of file will determine whether to recurse or not
            for (const info of infos) {
                const child = iter.get_child(info);
                const type = info.get_file_type();

                let branch;

                switch (type) {
                    case Gio.FileType.REGULAR:
                    case Gio.FileType.SYMBOLIC_LINK:
                        branch = deleteFile(child, cancellable);
                        break;

                    case Gio.FileType.DIRECTORY:
                        branch = deleteDirectory(child, cancellable);
                        break;

                    default:
                        continue;
                }

                branches.push(branch);
            }
        }

        await Promise.all(branches);
    } catch (e) {
        // We may ignore these errors, since a missing file does not need to be
        // deleted, and we may ignore a failure to recurse into a regular file
        if (!e.matches(Gio.IOErrorEnum, Gio.IOErrorEnum.NOT_FOUND) &&
            !e.matches(Gio.IOErrorEnum, Gio.IOErrorEnum.NOT_DIRECTORY))
            throw e;
    } finally {
        // We can return the Promise for deleting the top-level file
        return deleteFile(file, cancellable);
    }
}
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Last Updated: 1/28/2022, 10:52:31 PM
Contributors: Evan Welsh, Andy Holmes, Evan Welsh, Romain Vigier