extensions/git/src/util.ts/grep
export async function grep(filename: string, pattern: RegExp): Promise<boolean> {
	return new Promise<boolean>((c, e) => {
		const fileStream = createReadStream(filename, { encoding: 'utf8' });
		const stream = byline(fileStream);
		stream.on('data', (line: string) => {
			if (pattern.test(line)) {
				fileStream.close();
				c(true);
			}
		});

		stream.on('error', e);
		stream.on('end', () => c(false));
	});
}