units(1) - NetBSD Manual Pages

UNITS(1)                NetBSD General Commands Manual                UNITS(1)


NAME

     units -- conversion program


SYNOPSIS

     units [-Llqv] [-f filename] [[count] from-unit to-unit]


DESCRIPTION

     units 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 and arguments are supported:

           -f filename   Specifies the name of the units data file to load.

           -l or -L      List all unit definitions to the standard output,
                         instead of performing any conversions.  The result
                         may include error messages and comments, beginning
                         with `/'.

                         With the -l option, unit definitions will be listed
                         in a format almost identical to the the units data
                         file that was loaded, except that comments will be
                         removed, spacing may be changed, and lines may be re-
                         ordered.

                         With the -L option, all unit definitions will be
                         reduced to a form that depends on only a few primi-
                         tive units (such as m, kg, sec).

           -q            Suppresses prompting of the user for units and the
                         display of statistics about the number of units
                         loaded.

           -v            Prints the version number.

           [count] 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.  Specifying count and from-unit as two
                         separate arguments is equivalent to embedding both
                         parts inside a single from-unit argument, with the
                         parts separated by a space.

     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 indicat-
     ing 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.

NetBSD 8.0                      January 6, 2013                     NetBSD 8.0