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NetBSD 6.1.5 - man page for units (netbsd section 1)

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UNITS(1)			   BSD General Commands Manual				 UNITS(1)

NAME
     units -- conversion program

SYNOPSIS
     units [-f filename] [-qv] [[count] from-unit to-unit]

DESCRIPTION
     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
		 * 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 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.

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 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.

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 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
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