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36 lines
1 KiB
Markdown
36 lines
1 KiB
Markdown
# An implementation of the unix "cat" program
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## Concepts
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- Use the Deno runtime API to output the contents of a file to the console.
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- [Deno.args](https://doc.deno.land/builtin/stable#Deno.args) accesses the
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command line arguments.
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- [Deno.open](https://doc.deno.land/builtin/stable#Deno.open) is used to get a
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handle to a file.
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- [Deno.copy](https://doc.deno.land/builtin/stable#Deno.copy) is used to
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transfer data from the file to the output stream.
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- Files should be closed when you are finished with them
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- Modules can be run directly from remote URLs.
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## Example
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In this program each command-line argument is assumed to be a filename, the file
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is opened, and printed to stdout (e.g. the console).
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```ts
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/**
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* cat.ts
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*/
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for (let i = 0; i < Deno.args.length; i++) {
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const filename = Deno.args[i];
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const file = await Deno.open(filename);
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await Deno.copy(file, Deno.stdout);
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file.close();
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}
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```
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To run the program:
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```shell
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deno run --allow-read https://deno.land/std@$STD_VERSION/examples/cat.ts /etc/passwd
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```
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