UNITS(1) | General Commands Manual | UNITS(1) |
units | [-f filename] [-qv] [[count] from-unit to-unit] |
The following options are supported:
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:
“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 way as standard units, but with a trailing dash at the end of the prefix name.
Also, some pairs of units that have the same dimensionality are nonetheless used to measure different things and attempting to convert between them may require additional fudge factors or be entirely meaningless. For example, torque and energy have the same dimensionality, but attempting to convert torque in newton-meters to energy in joules is nonsensical. There is no practical way for units to warn about these issues either.
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.
April 3, 2011 | NetBSD 6.1 |