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## An implementation of the unix "cat" program
In this program each command-line argument is assumed to be a filename, the file
is opened, and printed to stdout.
```ts
for (let i = 0; i < Deno.args.length; i++) {
let filename = Deno.args[i];
let file = await Deno.open(filename);
await Deno.copy(file, Deno.stdout);
file.close();
}
```
The `copy()` function here actually makes no more than the necessary kernel ->
userspace -> kernel copies. That is, the same memory from which data is read
from the file, is written to stdout. This illustrates a general design goal for
I/O streams in Deno.
Try the program:
```shell
deno run --allow-read https://deno.land/std/examples/cat.ts /etc/passwd
```
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