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nosh: an experimental shell based on Node.js

nosh is essentially a normal Node.js REPL, except any function not already defined in the REPL context can be used to run an executable from your PATH:

> ls()
README.md
bin
node_modules
package.json
yarn.lock
undefined

The function takes optional arguments that are passed along:

> echo("hello world")
hello world

By default the function will print stdout and stderr and return an object that acts like a Promise (resolves or rejects when the command finishes). The REPL understands promises, and waits for it to resolve before printing the result and allowing the user to continue entering commands.

The returned object also has other useful functionality you can chain.

You can chain other commands, in which case stdout of the process is piped to stdin of the next process, like the | operator in most shells:

> echo("hello world").cat()
hello world

(equivalent to echo "hello world" | cat)

This works for any length pipeline, of course:

> echo("hello world").cat().cat().cat().wc()
    1       2      12

You can call .lines() to get a promise that resolves to an array of lines:

> ls().lines()
[ 'README.md', 'bin', 'node_modules', 'package.json', 'yarn.lock' ]

Or .string() to get the output as a single string:

> ls().string()
'README.md\nbin\nnode_modules\npackage.json\nyarn.lock'

Non-zero exit codes will cause the promise to reject:

> sh("-c", "false")
Thrown: 1

(this example uses sh("-c", "false") instead of false directly, because the latter is already defined in JavaScript)

You can instead call .code() to not reject, but instead return a promise that resolves to the exit code:

> sh("-c", "false").code()
1

(equivalent to sh -c "false"; echo $?)

"Command substitution" works, so you can pass any command as an argument to another command:

> echo(echo("hello world"))
hello world

(equivalent to echo(await echo("hello world").string()), or echo $(echo "hello world") in most shells)

"Process substition" also works, so you can pass the output of a command as a file to another command:

> cat(echo("hello world").stdout)
hello world
> echo(echo("hello").stdout)
/dev/fd/3

(equivalent to cat <(echo "hello world") in most shells)

In fact, this works with any Stream, not just stdout of sub-processes:

> cat(require("net").connect(23, towel.blinkenlights.nl))

TODO

  • Observables?
  • Support set -e, set -o pipefail, and various other shell behaviors
  • Support top-level await
  • Support various other helper methods on Process.
  • Alternative syntaxes (``sh`echo hello```)
  • History (currently only works on Node 11)
  • Pick a name that's available in NPM