Terminal SGR Indexed Color Field Parser

Description

Parse exactly one SGR 38/48;5;n indexed color field, not an arbitrary SGR stream or terminal palette lookup.

Terminal escape sequences can encode cursor commands, text styles and other controls inside ordinary text. SGR changes selected graphic attributes; CSI and OSC tokens have different framing. These tools operate on explicit strings and records, with a deliberately limited parser or style model rather than an emulated screen.^[1]

Parse exactly one SGR 38/48;5;n indexed color field, not an arbitrary SGR stream or terminal palette lookup.

When to use this tool

Use this tool to parse exactly one SGR 38/48;5;n indexed color field, not an arbitrary SGR stream or terminal palette lookup.

How to use the tool and how it works

Enter parameters using the field definitions below.
Run the operation. Correct input errors before interpreting an output.
Read result.background, result.index. Use the ordering, boundary rules and absence conditions described below.

Require exactly [38 or 48, 5, index], validate index from 0 through 255, and return it with a background flag.^[2]

Input field	Meaning and units	Accepted input
parameters	Explicit numeric SGR parameters, in sequence order.	Dense list of at most 128 finite numbers; integer/shape constraints above also apply.

Output field	Interpretation
result	Object containing the named fields below.
result.background	True for a background-color field, false for foreground.
result.index	Palette color index from 0 through 255.

json

{
  "input": {
    "parameters": [
      38,
      5,
      200
    ]
  },
  "output": {
    "result": {
      "background": false,
      "index": 200
    }
  }
}

Limitations and assumptions

Palette appearance depends on the terminal; this records an index rather than an RGB color.
Source spans use zero-based UTF-16 offsets with exclusive ends; byte totals, where returned, use UTF-8. Escape tokens are represented as JSON escapes in the example and are not executed by this description.
Every declared top-level input field is required and unexpected fields are rejected. Ordinary strings are limited to 8,192 UTF-16 code units and lists to 128 entries, with tighter operation-specific bounds where stated. JSON text has bounded nesting and node counts.
Numeric outputs must be finite and no larger in absolute magnitude than the safe-integer limit; operations returning exact large integers use decimal text. Positions are zero-based and spans end exclusively unless the operation explicitly states a different convention.

Alternative or Complementary methods

Use token inspection for source offsets and style replay for the supported attributes. A real terminal emulator is needed to determine screen contents, terminal-specific rendering or device behavior.

References

ECMA-48: Control Functions for Coded Character Sets — Ecma International
Tool behavior and example: Terminal SGR Indexed Color Field Parser — tool.io

Similar or alternative tools

Terminal SGR RGB Color Field Parser
Parse exactly one SGR 38/48;2;r;g;b truecolor field with byte channels; no colon syntax, color-space field or terminal gamut guarantee.
Terminal SGR Background Color Token
Format an explicit 0–255 indexed SGR background color field; no RGB palette mapping or terminal display guarantee.