UNITS(1) BSD General Commands Manual UNITS(1)
units -- conversion program
units [-f filename] [-qv] [[count] from-unit to-unit]
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 Fahren-
heit, 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 sta-
tistics 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 com-
mand 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
You have: cm^3
You want: gallons
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
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 defi-
nitions 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
``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.
/usr/share/misc/units.lib the standard units library
Adrian Mariano <firstname.lastname@example.org> or <email@example.com>
While units can be used as a calculator for many unit-related computations, caution is
required: many computations require additional constant factors deriving from the physics
(or chemistry or whatever) of the situation. As these factors are dimensionless, units can-
not itself either provide them or warn the user when they have been forgotten. For example,
one joule is one kilogram meter squared per second squared, by definition; however, the
kinetic energy of a one-kilogram object moving at one meter per second is half a joule, not
one joule, because of a dimensionless factor that arises from integration.
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.
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 multiply-
ing several terms.
The user must use '|' to indicate division of numbers and '/' to indicate division of sym-
bols. 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.
BSD April 3, 2011 BSD