units -- conversion program
units [-f filename] [-qv] [from-unit to-unit]
The following options are available:
Specify the name of the units data file to load.
-q Suppress prompting of the user for units and the display of statistics
about the number of units loaded.
-v Print the version number.
Allow 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.
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 Celsius to Fahrenheit,
for example. It works interactively by prompting the user for input:
You have: meters
You want: feet
You have: cm^3
You want: gallons
You have: meters/s
You want: furlongs/fortnight
You have: 1|2 inch
You want: cm
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
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
'pound force' 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
units 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
Here is an example of a short units file that defines some basic units.
minute 60 sec
hour 60 min
inch 0.0254 m
ft 12 inches
mile 5280 ft
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.
/usr/share/misc/units.lib the standard units library
Adrian Mariano <email@example.com>
FreeBSD 5.2.1 July 14, 1993 FreeBSD 5.2.1 [ Back ]