An implementation of the unix “cat” program

Concepts

  • Use the Deno runtime API to output the contents of a file to the console
  • Deno.args accesses the command line arguments
  • Deno.open is used to get a handle to a file
  • Deno.copy is used to transfer data from the file to the output stream
  • Files should be closed when you are finished with them
  • Modules can be run directly from remote URLs

Example

In this program each command-line argument is assumed to be a filename, the file is opened, and printed to stdout (e.g. the console).

  1. /**
  2. * cat.ts
  3. */
  4. for (let i = 0; i < Deno.args.length; i++) {
  5. const filename = Deno.args[i];
  6. const file = await Deno.open(filename);
  7. await Deno.copy(file, Deno.stdout);
  8. file.close();
  9. }

To run the program:

  1. deno run --allow-read https://deno.land/std@$STD_VERSION/examples/cat.ts /etc/passwd