si

NAME

si - parse, convert, and format physical quantities using SI units

SYNOPSIS

si [OPTIONS] VALUE
si --completions SHELL
si --version
si --help

DESCRIPTION

si is a command-line utility for parsing, converting, and formatting physical quantities expressed using the International System of Units (SI).

A quantity consists of a numeric value followed by a unit expression. Unit expressions support multiplication, division, exponentiation, and grouping using ASCII infix notation.

Quantities can be converted to a specified target unit, with dimensional compatibility checked during conversion. Output can be formatted in several representations, including UTF-8 encoded symbols, plain text, JSON, and LaTeX.

Numeric output supports configurable decimal precision and notation, including general, fixed-point, scientific, and E-notation.

OPTIONS

-n, --notation NOTATION

Set numeric notation. Supported values are general, fixed, scientific, e, and E.

-o, --output FORMAT

Set output format. Supported values are ascii, utf, json.

-p, --precision INTEGER

Set decimal precision (default: 3).

-u, --unit UNIT

Convert the quantity to the specified target unit representation.

-c, --completions SHELL

Generate shell completions for Bash or Zsh.

-v, --version

Display version information.

-h, --help

Display help information.

UNIT FORMATTING SYNTAX

The ‘-u‘, ‘--unit‘ option accepts a restricted syntax for specifying the target unit representation. Expressions must use ASCII unit symbols (eg. kg, us, ohm) and the following operators:

Symbols

	•		Multiplication *
	•		Division /
	•		Exponentiation ^
	•		Positive exponent +
	•		Negative exponent -
	•		Grouping ()

Valid examples

	•		kg*m/s^2
	•		mol/L
	•		uF/cm^2
	•		kWh
	•		m^3/s

Unicode operator variants, superscript exponents, alternative multiplication symbols, and alternative spellings of unit symbols are not supported.

UNIT PARSING SYNTAX

The parser accepts numeric quantities using fixed-point or scientific notation.

Unit expressions are parsed more permissively than the format syntax in order to accommodate common variations in notation.

Valid examples

	•		uohm*m^-2 -> µΩ·m⁻²
	•		μohmm*-2 -> µΩ·m⁻²
	•		µΩ·m⁻² -> µΩ·m⁻²
	•		uΩ×m^−2 -> µΩ·m⁻²
	•		μΩ⋅m⁻² -> µΩ·m⁻²

In addition to ASCII representations, the parser accepts the following UTF-8 encoded characters:

Multiplication

	•		ASTERISK (U+002A)
	•		ASTERISK OPERATOR (U+2217)
	•		STAR OPERATOR (U+22C6)
	•		MULTIPLICATION SIGN (U+00D7)
	•		MIDDLE DOT (U+00B7)
	•		HYPHENATION POINT (U+2027)
	•		BULLET OPERATOR (U+2219)
	•		DOT OPERATOR (U+22C5)
	•		LATIN LETTER SINOLOGICAL DOT (U+A78F)

Exponentiation

	•		CIRCUMFLEX ACCENT (U+005E)
	•		ASTERISK ASTERISK (U+002A U+002A)

Superscript digits

	•		SUPERSCRIPT ZERO (U+2070)
	•		SUPERSCRIPT ONE (U+00B9)
	•		SUPERSCRIPT TWO (U+00B2)
	•		SUPERSCRIPT THREE (U+00B3)
	•		SUPERSCRIPT FOUR (U+2074)
	•		SUPERSCRIPT FIVE (U+2075)
	•		SUPERSCRIPT SIX (U+2076)
	•		SUPERSCRIPT SEVEN (U+2077)
	•		SUPERSCRIPT EIGHT (U+2078)
	•		SUPERSCRIPT NINE (U+2079)

Exponent signs

	•		PLUS SIGN (U+002B)
	•		SUPERSCRIPT PLUS SIGN (U+207A)
	•		HYPHEN-MINUS (U+002D)
	•		HYPHEN (U+2010)
	•		MINUS SIGN (U+2212)
	•		SUPERSCRIPT MINUS (U+207B)

Grouping

	•		LEFT PARENTHESIS (U+0028)
	•		RIGHT PARENTHESIS (U+0029)
	•		LEFT CURLY BRACKET (U+007B)
	•		RIGHT CURLY BRACKET (U+007D)

Micro prefix

	•		MICRO SIGN (U+00B5)
	•		GREEK SMALL LETTER MU (U+03BC)

Ohm

	•		‘OHM SIGN‘ (U+2126)
	•		‘GREEK CAPITAL LETTER OMEGA‘ (U+03A9)

These variations are accepted when parsing input quantities. They do not necessarily apply to target unit expressions or determine how units are formatted in output.

Whitespace is permitted between expression components.