units-filter(1) is a parser for physical and chemical quantities

## SYNOPSIS

units-filter -s  -o  -l

## DESCRIPTION

units-filter

is a basic standalone parser written in C language, flex and bison. It inputs strings like "1.5e3 nN.m.s^-1" (it could be the time growth ratio of a torque) and outputs the value in standard SI unit, followed by the physical dimension of this value.

## OPTIONS

-s

Like Significant.

Takes in account the number of significant digits. For example 1.0 m contains 2 significant digits, while 0.00100 contains 3 significant digits. It is possible to enforce the number of significant digits by using a special syntax : if units-filter parses the input "1.0m#6", it interprets it as a value with exactly 6 significant digits, like "1.00000 m". The number following the # sign is the forced number of significant digits. The number of significant digits appears just before the last zero in the output of the command (this zero is a placeholder for future extensions).

-o

Like Output.

Outputs a correct representation of the physical quantity with its physical unit in the International System notation. There may be some simplification with usual units. For example, a newton will be represented by the unit N in place of m.kg.s^-2. The value is expressed as a floating number with one digit before the decimal point, and as many digits in the mantissa as necessary to fit the desired number of significant digits (see an example below). It is possible to enforce the output unit : just add a colon and the desired unit at the end of the input. If this unit is homogeneous with the former one, it will be used to format the output.

-l

Like LaTeX.

Outputs a correct representation of the physical quantity with its physical unit in the International System notation, in LaTeX language.

## EXAMPLES

Establish the SI value and unit exponent of a quantity in the mksa system:

~$echo 1.5e3 nN.m.s^-1 | units-filter 1.5e-6 2 1 -3 0 0 0 0 which means : 1.5e-6 (SI unit) m^2.kg.s^-3 Compare different physical quantities: ~$ e1=$(echo "1.2e-3 V" | units-filter) ~$ e2=$(echo "1200e3 nWb/s"| units-filter) ~$ if [ "$e1" = "$e2" ]; then echo ok; else echo ko; fi

ok

... which emphasizes that webers by unit time are the same as volts.

Playing with the number of significant digits:

~$echo "0.00100m" | src/units-filter -s 0.001 1 0 0 0 0 0 0 3 0 ~$ echo "0.00100m #2" | src/units-filter -s

0.001 1 0 0 0 0 0 0 2 0

Giving a value for the relative precision:

~$echo "1kV~2" | units-filter -o 1e+03 V +-2% Turning on the LaTeX output: ~$ echo "1kohm+-2%" | units-filter -l

1\times 10^{+03}\, \Omega \pm 2\,\%

Turning on the output of a canonical physical notation:

~$echo "1.0 m.kg.s^-2 #7" | units-filter -o 1.000000e+00N Choosing a non-standard unit for the output: ~$ echo 1800C:A.h| units-filter -o

5.000e-01 A.h

## KNOWN BUGS

Few units out of the mksa system are successfully parsed.