README.md

Introduction

This is a parser generator whose output is a parser which produces an AST for consumption by @orbital-frame/core.

Installing

npm install --save @orbital-frame/parser

The command grammar is a modified subset of bash's grammar:

• command
• options
  • short
  • long
• arguments
• pipes
• multiple commands per line
• command substitution
  • interpolated commands can be used as either arguments or option values
• variables
• functions
  • including optional lexical scoping

AST

The grammar can be found here.

Example

The command

CHANNEL="#random"; channel-history $CHANNEL | filter --user $(whoami)

parses to

{
   "type": "Program",
   "body": [
      {
         "type": "Assignment",
         "body": [
            "CHANNEL",
            "#random"
         ]
      },
      {
         "type": "Pipeline",
         "body": [
            {
               "type": "Command",
               "body": [
                  "channel-history",
                  {
                     "type": "Argument",
                     "body": [
                        {
                           "type": "Variable",
                           "body": [
                              "CHANNEL"
                           ]
                        }
                     ]
                  }
               ]
            },
            {
               "type": "Command",
               "body": [
                  "filter",
                  [
                     {
                        "type": "Option",
                        "body": [
                           "user",
                           {
                              "type": "Argument",
                              "body": [
                                 {
                                    "type": "Interpolation",
                                    "body": [
                                       {
                                          "type": "Pipeline",
                                          "body": [
                                             {
                                                "type": "Command",
                                                "body": [
                                                   "whoami"
                                                ]
                                             }
                                          ]
                                       }
                                    ]
                                 }
                              ]
                           }
                        ]
                     }
                  ]
               ]
            }
         ]
      }
   ]
}

Differences from bash

Orbital Frame uses a stricter grammar than bash and in doing so avoids some annoying and perhaps surprising edge cases.

---

In bash, variables are expanded in place so things like this are allowed:

ARG="-n"; echo $ARG test

which would allow -n to be used to specify an option. Orbital Frame, however, only allows variables to be used as arguments to commands and command options.

---

Bash allows evaluating strings as options so the following

echo "-n" test

will print "test" without a newline character while Orbital Frame passes both "-n" and "test" as arguments to echo

---

Bash also allows similar behavior with regards to command interpolation. In bash,

echo $(echo "-n ") test

will print "test" without a newline character while Orbital Frame passes both "-n" (the evaluation of the interpolated command) and "test" as arguments to echo.

---

Bash treats single- and double-quoted strings differently, where double-quoted strings allow interpolation and single-quoted strings do not. Orbital Frame doesn't allow string interpolation at all (at least for now).