3431172fa8
It turns out that units(1) is not as horrible to use in scripts
as I initially thought. When the --terse flag is combined
with an appropriate output format (set via --output-format),
units(1) is actually capable of producing very nice results.
For example:
units -o %0.f -t '4 gigabytes' bytes
is is just going to print out the expected value of 4294967296.
There is no time to waste. People have to know about it.
I am adding an example for this at the top of the examples section
because this is what users are most likely looking for.
Approved by: bcr (mentor)
Differential Revision: https://reviews.freebsd.org/D24096
475 lines
11 KiB
Groff
475 lines
11 KiB
Groff
.\" $FreeBSD$
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.Dd March 17, 2020
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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 calculator
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.Sh SYNOPSIS
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.Nm
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.Op Fl ehqtUVv
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.Op Fl f Ar unitsfile
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.Op Fl o Ar format
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.Op Ar from to
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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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It can only
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handle multiplicative or affine scale changes.
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.Pp
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.Nm
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can work interactively by prompting
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the user for input
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.Pq see Sx EXAMPLES
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or non-interactively, providing a conversion for given arguments
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.Ar from
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and
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.Ar to .
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.Pp
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The following options are available:
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.Bl -tag -width "from to"
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.It Fl e , Fl -exponential
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Same as
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.Fl o
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.Cm %6e
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(see the description of the
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.Fl o
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flag).
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.It Fl f Ar unitsfile , Fl -file Ar unitsfile
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Specify the name of the units data file to load.
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This option may be specified multiple times.
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.It Fl H Ar historyfile , Fl -history Ar historyfile
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Ignored, for compatibility with GNU units.
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.It Fl h , Fl -help
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Show an overview of options.
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.It Fl o Ar format , Fl -output-format Ar format
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Select the output format string by which numbers are printed.
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Defaults to
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.Dq Li %.8g .
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.It Fl q , Fl -quiet
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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 t , Fl -terse
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Only print the result.
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This is used when calling
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.Nm
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from other programs for easy to parse results.
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.It Fl U , Fl -unitsfile
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Print the location of the default unit file if it exists.
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Otherwise, print
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.Dq Units data file not found .
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.It Fl V , Fl -version
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Print the version number
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.Pq which is fixed at Dq Fx units ,
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the path to the units data file and exit.
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.It Fl v , Fl -verbose
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Print the units in the conversion output.
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Be more verbose in general.
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.It Ar from to
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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 result of the single specified conversion.
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Both arguments, i.e.,
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.Ar from
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and
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.Ar to ,
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can be just a unit
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.Pq e.g., Dq Cm cm ,
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a quantity
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.Pq e.g., Dq Cm 42 ,
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or a quantity with a unit
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.Pq e.g., Dq Cm 42 cm
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.El
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.Ss Mathematical operators
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.Bl -dash -compact
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.It
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Powers of units can be specified using the
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.Dq Ic ^
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character as shown in the example, or by simple concatenation:
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.Dq Ic cm3
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is
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equivalent to
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.Dq Ic cm^3 .
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See the
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.Sx BUGS
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section
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for details on the limitations of exponent values.
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.It
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Multiplication of units can be specified by using spaces
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.Pq Dq " " ,
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a dash
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.Pq Dq -
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or an asterisk
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.Pq Dq * .
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.It
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Division of units is indicated by the slash
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.Pq Dq Ic / .
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.It
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Division of numbers
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must be indicated using the vertical bar
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.Pq Dq Ic \&| Ns .
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.El
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.Pp
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Note that multiplication has a higher precedence than division,
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so
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.Dq Ic m/s/s
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is the same as
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.Dq Ic m/s^2
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or
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.Dq Ic m/s s .
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.Ss Units
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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
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.Dq Ic pound
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is a unit of mass.
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Compound names are run together
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so
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.Dq Ic pound force
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is a unit of force.
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The unit
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.Dq Ic ounce
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is also a unit of mass.
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The fluid ounce is
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.Dq Ic floz .
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British units that differ from
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their US counterparts are prefixed with
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.Dq br ,
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and currency is prefixed with its country name:
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.Dq Ic belgiumfranc ,
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.Dq Ic 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
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.Dq s
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or a trailing
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.Dq es
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and check again for a match.
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.Ss Units file format
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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
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.Dq \&!
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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
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.Dq #
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or
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.Dq /
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character at the beginning of a line.
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.Pp
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Prefixes are defined in the same way as standard units, but with
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a trailing dash
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.Pq Dq -
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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
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.Dq s
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or
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.Dq es ,
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then it will be checked 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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.Sh ENVIRONMENT
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.Bl -tag -width PATH
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.It Ev PATH
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The colon-separated list of root directories at which
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.Nm
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tries to find
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.Pa /usr/share/misc/definitions.units .
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.Pp
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For example if
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.Ev PATH
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is set to
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.Dq Li /tmp:/:/usr/local ,
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no
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.Fl f
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flags are provided, and
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.Pa /usr/share/misc/definitions.units
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is missing then
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.Nm
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tries to open the following files as the default units file:
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.Pa /tmp/usr/share/misc/definitions.units ,
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.Pa /usr/share/misc/definitions.units ,
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and
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.Pa /usr/local/usr/share/misc/definitions.units .
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.El
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.Sh FILES
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.Bl -tag -width /usr/share/misc/definitions.units -compact
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.It Pa /usr/share/misc/definitions.units
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The standard units file.
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.El
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.Sh EXIT STATUS
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.Ex -std
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.Sh EXAMPLES
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.Bl -tag -width 0n
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.It Sy Example 1 : No Simple conversion of units
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.Pp
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This example shows how to do simple conversions, for example from gigabytes
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to bytes:
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.Bd -literal -offset 2n
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.Li $ Ic units -o %0.f -t '4 gigabytes' bytes
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4294967296
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.Ed
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.Pp
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The
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.Fl o Cm %0.f
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part of the command is required to print the result in a non-scientific
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notation (e.g, 4294967296 instead of 4.29497e+09).
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.It Sy Example 2 : No Interactive usage
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.Pp
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Here is an example of an interactive session where the user is prompted for
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units:
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.Bd -literal -offset 2n
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.Li You have : Ic meters
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.Li You want : Ic feet
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* 3.2808399
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/ 0.3048
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.Li You have : Ic cm^3
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.Li You want : Ic gallons
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* 0.00026417205
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/ 3785.4118
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.Li You have : Ic meters/s
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.Li You want : Ic furlongs/fortnight
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* 6012.8848
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/ 0.00016630952
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.Li You have : Ic 1|2 inch
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.Li You want : Ic cm
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* 1.27
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/ 0.78740157
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.Li You have : Ic 85 degF
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.Li You want : Ic degC
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29.444444
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.Ed
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.It Sy Example 3 : No Difference between Do Ic \&| Dc No and Do Ic / Dc No division
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.Pp
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The following command shows how to convert half a meter to centimeters.
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.Bd -literal -offset 2n
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.Li $ Ic units '1|2 meter' cm
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* 50
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/ 0.02
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.Ed
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.Pp
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.Nm
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prints the expected result because the division operator for numbers
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.Pq Dq Li \&|
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was used.
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.Pp
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Using the division operator for units
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.Pq Dq Li /
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would result in an error:
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.Bd -literal -offset 2n
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.Li $ Ic units '1/2 meter' cm
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conformability error
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0.5 / m
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0.01 m
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.Ed
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.Pp
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It is because
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.Nm
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interprets
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.Dq Ic 1/2 meter
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as
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.Dq Ic 0.5/meter ,
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which is not conformable to
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.Dq Ic cm .
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.It Sy Example 4 : No Simple units file
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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 2n -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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.It Sy Example 5 : No Viewing units and conversions of the default units file
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The following shell one-liner allows the user to view the contents of the
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default units file:
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.Bd -literal -offset 2n
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.Li $ Ic less \&"$(units -U)"
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.Ed
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.El
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.Sh DIAGNOSTICS
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.Bl -diag
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.It can't find units file '%s'
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The default units file is not in its default location
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.Pq see Sx FILES
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and it is not present in any file tree starting with their roots at directories from
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.Ev PATH
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.Pq see Sx ENVIRONMENT .
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.It cap_rights_limit\&() failed
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See
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.Xr capsicum 4 .
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.It conformability error
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It is not possible to reduce the given units to one common unit:
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they are not conformable.
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Instead of a conversion,
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.Nm
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will display the reduced form for each provided unit:
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.Bd -literal -offset 2n
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.Li You have : Ic ergs/hour
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.Li You want : Ic 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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.It Could not initialize history
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See
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.Xr editline 3 .
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.It dupstr
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.Xr strdup 3
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failed.
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.It memory for prefixes exceeded in line %d
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Over 100 prefixes were defined.
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.It memory for units exceeded in line %d
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Over 1000 prefixes were defined.
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.It memory overflow in unit reduction
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The requested conversion involves too many units
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.Pq see Sx BUGS .
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.It redefinition of prefix '%s' on line %d ignored
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.No ""
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.It redefinition of unit '%s' on line %d ignored
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.No ""
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.It unexpected end of prefix on line %d
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.No ""
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.It unexpected end of unit on line %d
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.No ""
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.It Units data file not found
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The default units file is missing.
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.It unable to enter capability mode
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See
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.Xr capsicum 4 .
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.It unable to open units file '%s'
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One of the user-specified units files cannot be opened.
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.It unit reduces to zero
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.No ""
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.It unknown unit '%s'
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The provided unit cannot be found in the units file.
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.It WARNING: conversion of non-proportional quantities.
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.Nm
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may fail to convert
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.Ar from
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to
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.Ar to
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because the units are not proportional.
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The warning is printed when a quantity is a part of the
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.Ar to
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argument.
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It can be illustrated on an example of conversion from Fahrenheit to Celsius:
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.Bd -literal -offset 2n
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.Li $ Ic units \&"degF" \&"degC"
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(-> x*0.55555556g -17.777778g)
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(<- y*1.8g 32g)
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.Li $ Ic units \&"degF" \&"1 degC"
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WARNING: conversion of non-proportional quantities.
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(-> x*0.55555556g -17.777778g)
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(<- y*1.8g 32g)
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.Li $ Ic units \&"1 degF" \&"1 degC"
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WARNING: conversion of non-proportional quantities.
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-17.222222
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.Ed
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.El
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.Sh SEE ALSO
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.Xr bc 1
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.Sh HISTORY
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The
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.Nm
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first appeared in
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.Nx
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and was ported to
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.Fx 2.2.0 .
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.Pp
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The manual page was significantly rewritten in
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.Fx 13.0
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by
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.An Mateusz Piotrowski Aq Mt 0mp@FreeBSD.org .
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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
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.Dq /
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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
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.Dq Ic \&|
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to indicate division of numbers and
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.Dq Ic /
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to 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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.Pp
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It is not possible to convert a negative value.
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.Pp
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The
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.Nm
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program
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does not handle reductions of long lists of units very well:
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.Bd -literal -offset 2n
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.Li $ Ic units \&"$(yes m | head -n 154)" \&"$(yes cm | head -n 154)"
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* 1e+308
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/ 1e-308
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.Li $ Ic units \&"$(yes m | head -n 333)" \&"$(yes cm | head -n 333)"
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* inf
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/ 0
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.Li $ Ic units \&"$(yes m | head -n 500)" \&"$(yes cm | head -n 500)"
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units: memory overflow in unit reduction
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conformability error
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1 m^500
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1 centi cm^499
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.Li $ Ic units \&"$(yes m | head -n 501)" \&"$(yes cm | head -n 501)"
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units: memory overflow in unit reduction
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units: memory overflow in unit reduction
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units: memory overflow in unit reduction
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conformability error
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1 m^500
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1 centi cm^499
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.Ed
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