UNITS(1) BSD General Commands Manual UNITS(1)NAMEunits — conversion program
SYNOPSISunits [-f filename] [-qv] [[count] from-unit to-unit]
DESCRIPTIONunits converts quantities expression in various scales to their equiva‐
lents 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”. Mul‐
tiplication 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 met‐
ric 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 trail‐
ing dash at the end of the prefix name.
FILES
/usr/share/misc/units.lib the standard units library
AUTHORS
Adrian Mariano ⟨adrian@cam.cornell.edu⟩ or ⟨mariano@geom.umn.edu⟩
CAVEATS
While units can be used as a calculator for many unit-related computa‐
tions, caution is required: many computations require additional constant
factors deriving from the physics (or chemistry or whatever) of the situ‐
ation. As these factors are dimensionless, units cannot itself either
provide them or warn the user when they have been forgotten. For exam‐
ple, one joule is one kilogram meter squared per second squared, by defi‐
nition; 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 dimen‐
sionless factor that arises from integration.
Also, some pairs of units that have the same dimensionality are nonethe‐
less 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 attempt‐
ing to convert torque in newton-meters to energy in joules is nonsensi‐
cal. There is no practical way for units to warn about these issues
either.
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.
BSD April 3, 2011 BSD
