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# 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](https://doc.deno.land/builtin/stable#Deno.args) accesses the
command line arguments.
- [Deno.open](https://doc.deno.land/builtin/stable#Deno.open) is used to get a
handle to a file.
- [Deno.copy](https://doc.deno.land/builtin/stable#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).
```ts
/**
* cat.ts
*/
for (const filename of Deno.args) {
const file = await Deno.open(filename);
await Deno.copy(file, Deno.stdout);
file.close();
}
```
To run the program:
```shell
deno run --allow-read https://deno.land/std@$STD_VERSION/examples/cat.ts /etc/passwd
```
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