Deno for scripting

deno-script.md

Deno for scripting

Foreword

It is largely inspired by kscript. The idea is to leverage the scripting abilities of javascript using Deno. I feel that scripting can be so much fun with Deno as:

• It can import modules from any location on the web,
• It is secure by default. Imported module can run in sandbox.
• It is Supports TypeScript out of the box.
• It is much more that Node

Requirement

• Installing deno.
• Os: Mac, linux
• Make sure that Deno is on the bin path

Script Input Modes

The main mode of operation is deno run <script>. The <script> can be a Javascript *.js or Typescritpt *.ts file , a script URL, - for stdin, a process substitution file handle.

Interpreter Usage

To use Deno as interpreter for a script:

• create an executable in the bin directory /usr/local/bin called deno-script(call it as you want)

#!/bin/bash
#In deno-script
deno run $@

Make it executable

$ chmod u+x deno-script;

• Now when create a script just point todeno-script in the shebang line of your scripts:

#!/usr/bin/env deno-script
// In hello.js
console.log("hello world")
for (let arg of Deno.args) {
    console.log(`arg: ${arg}`)
}

Make it executable

$ chmod u+x hello.js;

Execute it

$ ./hello.js;

You can me a similar script doing the lsjob using Deno API’s!

#!/bin/bash deno-script

for (const dirEntry of Deno.readDirSync("./")) {
      console.log(dirEntry.name);
}

If we execute this script, we will have a error

error: Uncaught PermissionDenied: read access to "./", run again with the --allow-read flag
    at unwrapResponse (rt/10_dispatch_json.js:25:13)
    at sendSync (rt/10_dispatch_json.js:52:12)
    at Object.readDirSync (rt/30_fs.js:105:16)
    at file:///Users/jpi/dev/deno/deno-ls.js:3:29

This is were Deno shine! Deno will not you implicitly have access to to your directories. You need to explicitly ask the permission to Deno.

Your could specify it in the shebang:

#!/bin/bash deno-script --allow-read

For more about Deno security go here.

Inlined Usage

To use kscript in a workflow without creating an additional script file, you can also use one of its supported modes for /inlined usage/.

For the we will modify deno-script a bit

#!/bin/bash
if [[ $1 =~ (--inline|-i) ]]; then
    deno run <(echo $2) "${@:3}"
elif [[ $1 =~ (--pipe|-p) ]]; then
    while read arg; do
        deno run <(echo $2) "$arg"
    done
else
    deno run $@
fi

The following modes are supported:

• Directly provide a js scriptlet as argument

$ deno-script -i "console.log('hello', Deno.args[0])" JP

I can use pipe with it

 ls | xargs -L 1 deno-script -i 'console.log(`file:   ${Deno.args[0]}`)'

-L 1 of options of xargs is to manage the execution of each stream pipe elements (see)

You could get the same result with -pof --p option

ls -la | deno-script -p "console.log('hello', Deno.args[0])"

You can manage several arguments

deno-script -i '
for (let arg of Deno.args) {
    console.log(`arg: ${arg}`)
} ' arg1 arg2 arg3

• Pipe a js snippet into Deno and instruct it to read from stdin by using - as script argument

echo '
console.log("hello world")
' | deno-script -

• Using heredoc (preferred solution for inlining) which gives you some more flexibility to also use single quotes in your script:

deno-script - <<"EOF"
console.log("It's a beautiful day!")
EOF

• Since the piped content is considered as a regular script it can also have dependencies

deno-script - <<"EOF"
  import {hello} from "https://raw.githubusercontent.com/jiraguha/js-playgroud/master/hello-lib.ts"
  hello("JP")
EOF

We could continue and do much more…

nice!