units converts quantities expression in various scales to their equivalents in other scales.
units can only handle multiplicative scale changes. It cannot convert Centigrade to Fahrenheit, for example.
The following options are supported:
-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.
-v
Prints the version number.
from-unit to-unit
Allows a single unit conversion to be done directly from the command line. No prompting will occur. units will print out only the result of this single conversion. The count argument can be prepended to the from-unit or it can be separate.
units 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
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”. If the user enters 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
g
acceleration of gravity
water
pressure per unit height of water
mercury
pressure per unit height of mercury
“pound” is a unit of mass. Compound names are run together so “poundforce” is a unit of force. 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.
All of these definitions can be read in the standard units file, or you can supply your own file. A unit is specified on a single line by giving its name and an equivalence. One should 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.
units will not detect infinite loops that could be caused by careless unit definitions.
Prefixes are defined in the same was as standard units, but with a trailing dash at the end of the prefix name.