191 lines
5.3 KiB
Groff
191 lines
5.3 KiB
Groff
.\" $FreeBSD$
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.Dd April 14, 2014
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.Dt UNITS 1
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.Os
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.Sh NAME
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.Nm units
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.Nd conversion program
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.Sh SYNOPSIS
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.Nm
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.Op Fl f Ar filename
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.Op Fl qvUV
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.Op Ar from-unit to-unit
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.Sh OPTIONS
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The following options are available:
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.Bl -tag -width indent
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.It Fl f Ar filename
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Specify the name of the units data file to load.
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.It Fl q
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Suppress prompting of the user for units and the display of statistics
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about the number of units loaded.
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.It Fl U
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If the default unit file exists prints its location. If not, print
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.Qo
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Units data file not found
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.Qc
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.It Fl V
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Print the version number, usage, and then exit.
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.It Ar from-unit to-unit
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Allow a single unit conversion to be done directly from the command
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line.
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The program will not print prompts.
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It will print out the
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result of the single specified conversion.
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.It Fl v
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Print the units in the conversion output. Be more verbose in general.
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.El
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.Sh DESCRIPTION
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The
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.Nm
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program converts quantities expressed in various scales to
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their equivalents in other scales.
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The
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.Nm
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program can only
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handle multiplicative or affine scale changes.
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It works interactively by prompting
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the user for input:
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.Bd -literal
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You have: meters
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You want: feet
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* 3.2808399
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/ 0.3048
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You have: cm^3
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You want: gallons
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* 0.00026417205
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/ 3785.4118
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You have: meters/s
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You want: furlongs/fortnight
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* 6012.8848
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/ 0.00016630952
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You have: 1|2 inch
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You want: cm
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* 1.27
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/ 0.78740157
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You have: 85 degF
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You want: degC
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29.444444
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.Ed
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.Pp
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Powers of units can be specified using the '^' character as shown in
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the example, or by simple concatenation: 'cm3' is equivalent to 'cm^3'.
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Multiplication of units can be specified by using spaces, a dash or
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an asterisk.
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Division of units is indicated by the slash ('/').
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Note that multiplication has a higher precedence than division,
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so 'm/s/s' is the same as 'm/s^2' or 'm/s s'.
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Division of numbers
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must be indicated using the vertical bar ('|').
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To convert half a
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meter, you would write '1|2 meter'.
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If you write '1/2 meter' then the
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units program would interpret that as equivalent to '0.5/meter'.
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If you enter incompatible unit types, the units program will
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print a message indicating that the units are not conformable and
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it will display the reduced form for each unit:
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.Bd -literal
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You have: ergs/hour
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You want: fathoms kg^2 / day
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conformability error
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2.7777778e-11 kg m^2 / sec^3
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2.1166667e-05 kg^2 m / sec
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.Ed
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.Pp
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The conversion information is read from a units data file.
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The default
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file includes definitions for most familiar units, abbreviations and
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metric prefixes.
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Some constants of nature included are:
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.Pp
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.Bl -column -offset indent -compact "mercury"
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.It "pi ratio of circumference to diameter"
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.It "c speed of light"
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.It "e charge on an electron"
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.It "g acceleration of gravity"
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.It "force same as g"
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.It "mole Avogadro's number"
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.It "water pressure per unit height of water"
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.It "mercury pressure per unit height of mercury"
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.It "au astronomical unit"
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.El
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.Pp
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The unit 'pound' is a unit of mass.
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Compound names are run together
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so 'pound force' is a unit of force.
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The unit 'ounce' is also a unit
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of mass.
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The fluid ounce is 'floz'.
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British units that differ from
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their US counterparts are prefixed with 'br', and currency is prefixed
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with its country name: 'belgiumfranc', 'britainpound'.
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When searching
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for a unit, if the specified string does not appear exactly as a unit
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name, then
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.Nm
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will try to remove a trailing 's' or a
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trailing 'es' and check again for a match.
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.Pp
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To find out what units are available read the standard units file.
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If you want to add your own units you can supply your own file.
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A unit is specified on a single line by
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giving its name and an equivalence.
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Be careful to define
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new units in terms of old ones so that a reduction leads to the
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primitive units which are marked with '!' characters.
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The
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.Nm
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program will not detect infinite loops that could be caused
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by careless unit definitions.
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Comments in the unit definition file
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begin with a '/' character at the beginning of a line.
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.Pp
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Prefixes are defined in the same was as standard units, but with
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a trailing dash at the end of the prefix name.
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If a unit is not found
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even after removing trailing 's' or 'es', then it will be checked
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against the list of prefixes.
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Prefixes will be removed until a legal
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base unit is identified.
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.Pp
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Here is an example of a short units file that defines some basic
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units.
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.Pp
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.Bl -column -offset indent -compact "minute"
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.It "m !a!"
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.It "sec !b!"
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.It "micro- 1e-6"
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.It "minute 60 sec"
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.It "hour 60 min"
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.It "inch 0.0254 m"
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.It "ft 12 inches"
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.It "mile 5280 ft"
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.El
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.Sh FILES
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.Bl -tag -width /usr/share/misc/units.lib -compact
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.It Pa /usr/share/misc/units.lib
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the standard units library
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.El
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.Sh AUTHORS
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.An Adrian Mariano Aq Mt adrian@cam.cornell.edu
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.Sh BUGS
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The effect of including a '/' in a prefix is surprising.
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.Pp
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Exponents entered by the user can be only one digit.
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You can work around this by multiplying several terms.
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.Pp
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The user must use | to indicate division of numbers and / to
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indicate division of symbols.
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This distinction should not
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be necessary.
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.Pp
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The program contains various arbitrary limits on the length
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of the units converted and on the length of the data file.
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.Pp
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The program should use a hash table to store units so that
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it does not take so long to load the units list and check
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for duplication.
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