UNITS(1)

NAME
units - conversion program

SYNTAX
units [-f filename] [-q] [to-unit from-unit]

SUMMARY

-f filename
    Specifies the name of the units data file to load.

-q  Suppresses prompting of the user for units and the display of statistics about the number of units loaded.

from-unit to-unit
    Allows a single unit conversion to be done directly from the command line. The program will not print prompts. It will print out the result of the single specified conversion.

DESCRIPTION
The units program converts quantities expressed in various scales to their equivalents in other scales. The units program can only handle multiplicative scale changes. It cannot convert Centigrade to Fahrenheit, for example. It works interactively by prompting the user for input:
    You have: meters
    You want: feet
            * 3.2808399
            / 0.3048
    You have: cm^3
    You want: gallons
            * 0.00026417205
            / 3785.4118
    You have: meters/s
    You want: furlongs/fortnight
            * 6012.8848
            / 0.00016630952
    You have: 1|2 inch
    You want: cm
            * 1.27
            / 0.78740157
Powers of units can be specified using the '^' character as shown in the example, or by simple concatenation: 'cm3' is equivalent to 'cm^3'. Multiplication of units can be specified by using spaces, a dash or an asterisk. Division of units is indicated by the slash ('/'). Note that multiplication has a higher precedence than division, so 'm/s/s' is the same as 'm/s^2' or 'm/s s'. Division of numbers must be indicated using the vertical bar ('|'). To convert half a meter, you would write '1|2 meter'. If you write '1/2 meter' then the units program would interpret that as equivalent to '0.5/meter'. If you enter incompatible unit types, the units program will print a message indicating that the units are not conformable and it will display the reduced form for each unit:
    You have: ergs/hour
    You want: fathoms kg^2 / day
    conformability error
            2.7777778e-11 kg m^2 / sec^3
            2.1166667e-05 kg^2 m / sec

The conversion information is read from a units data file. The default file includes definitions for most familiar units, abbreviations and metric prefixes. Some constants of nature included are:
pi	ratio of circumference to diameter
c	speed of light
e	charge on an electron
g	acceleration of gravity
force	same as g
mole	Avogadro's number
water	pressure per unit height of water
mercury	pressure per unit height of mercury
au	astronomical unit
The unit 'pound' is a unit of mass. Compound names are run together so 'poundforce' is a unit of force. The unit 'ounce' is also a unit of mass. The fluid ounce is 'floz'. British units that differ from their US counterparts are prefixed with 'br', and currency is prefixed with its country name: 'belgiumfranc', 'britainpound'. When searching for a unit, if the specified string does not appear exactly as a unit name, then the units program will try to remove a trailing 's' or a trailing 'es' and check again for a match.

To find out what units are available read the standard units file. If you want to add your own units you can supply your own file. A unit is specified on a single line by giving its name and an equivalence. Be careful to define new units in terms of old ones so that a reduction leads to the primitive units which are marked with '!' characters. The units program will not detect infinite loops that could be caused by careless unit definitions. Comments in the unit definition file begin with a '/' character at the beginning of a line.

Prefixes are defined in the same was as standard units, but with a trailing dash at the end of the prefix name. If a unit is not found even after removing trailing 's' or 'es', then it will be checked against the list of prefixes. Prefixes will be removed until a legal base unit is identified.

Here is an example of a short units file that defines some basic units.
m	!a!
sec	!b!
micro-	1e-6
minute	60 sec
hour	60 min
inch	0.0254 m
ft	12 inches
mile	5280 ft

BUGS

The effect of including a '/' in a prefix is surprising.

Exponents entered by the user can be only one digit. You can work around this by multiplying several terms.

The user must use | to indicate division of numbers and / to indicate division of symbols. This distinction should not be necessary.

The program contains various arbitrary limits on the length of the units converted and on the length of the data file.

The program should use a hash table to store units so that it doesn't take so long to load the units list and check for duplication.

FILES
/usr/share/misc/units.lib - the standard units library

AUTHOR
Adrian Mariano (adrian@cam.cornell.edu)