Checking for file existence

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When creating files it can be useful to first ensure that such a file doesn't already exist. There are a number of ways to do this.

Use the `exists` utility from the std library to check for existence of a file or folder. Note: Can create a race condition if followed by file operation. Consider the alternative below.

import { exists } from "jsr:@std/fs/exists";
await exists("./this_file_or_folder_exists"); // true
await exists("./this_file_or_folder_does_not_exist"); // false

We can also use this function to check if the item on a path is a file or a directory

await exists("./file", { isFile: true }); // true
await exists("./directory", { isFile: true }); // false

Do not use the above function if performing a check directly before another operation on that file. Doing so creates a race condition. The `exists` function is not recommended for that usecase. Consider this alternative which checks for existence of a file without doing any other filesystem operations.

try {
  const stats = await Deno.lstat("example.txt");
} catch (err) {
  if (!(err instanceof Deno.errors.NotFound)) {
    throw err;
  }
  console.log("File does not exist");
}

Run this example locally using the Deno CLI:

deno run --allow-read --allow-write https://docs.deno.com/examples/scripts/checking_file_existence.ts

Checking for file existence

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