usr.bin/units/units.1

.\" $FreeBSD$
.Dd March 17, 2020
.Dt UNITS 1
.Os
.Sh NAME
.Nm units
.Nd conversion calculator
.Sh SYNOPSIS
.Nm
.Op Fl ehqtUVv
.Op Fl f Ar unitsfile
.Op Fl o Ar format
.Op Ar from to
.Sh DESCRIPTION
The
.Nm
program converts quantities expressed in various scales to
their equivalents in other scales.
It can only
handle multiplicative or affine scale changes.
.Pp
.Nm
can work interactively by prompting
the user for input
.Pq see Sx EXAMPLES
or non-interactively, providing a conversion for given arguments
.Ar from
and
.Ar to .
.Pp
The following options are available:
.Bl -tag -width "from to"
.It Fl e , Fl -exponential
Same as
.Fl o
.Cm %6e
(see the description of the
.Fl o
flag).
.It Fl f Ar unitsfile , Fl -file Ar unitsfile
Specify the name of the units data file to load.
This option may be specified multiple times.
.It Fl H Ar historyfile , Fl -history Ar historyfile
Ignored, for compatibility with GNU units.
.It Fl h , Fl -help
Show an overview of options.
.It Fl o Ar format , Fl -output-format Ar format
Select the output format string by which numbers are printed.
Defaults to
.Dq Li %.8g .
.It Fl q , Fl -quiet
Suppress prompting of the user for units and the display of statistics
about the number of units loaded.
.It Fl t , Fl -terse
Only print the result.
This is used when calling
.Nm
from other programs for easy to parse results.
.It Fl U , Fl -unitsfile
Print the location of the default unit file if it exists.
Otherwise, print
.Dq Units data file not found .
.It Fl V , Fl -version
Print the version number
.Pq which is fixed at Dq Fx units ,
the path to the units data file and exit.
.It Fl v , Fl -verbose
Print the units in the conversion output.
Be more verbose in general.
.It Ar from to
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.
Both arguments, i.e.,
.Ar from
and
.Ar to ,
can be just a unit
.Pq e.g., Dq Cm cm ,
a quantity
.Pq e.g., Dq Cm 42 ,
or a quantity with a unit
.Pq e.g., Dq Cm 42 cm
.El
.Ss Mathematical operators
.Bl -dash -compact
.It
Powers of units can be specified using the
.Dq Ic ^
character as shown in the example, or by simple concatenation:
.Dq Ic cm3
is
equivalent to
.Dq Ic cm^3 .
See the
.Sx BUGS
section
for details on the limitations of exponent values.
.It
Multiplication of units can be specified by using spaces
.Pq Dq " " ,
a dash
.Pq Dq -
or an asterisk
.Pq Dq * .
.It
Division of units is indicated by the slash
.Pq Dq Ic / .
.It
Division of numbers
must be indicated using the vertical bar
.Pq Dq Ic \&| Ns .
.El
.Pp
Note that multiplication has a higher precedence than division,
so
.Dq Ic m/s/s
is the same as
.Dq Ic m/s^2
or
.Dq Ic m/s s .
.Ss Units
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:
.Pp
.Bl -column -offset indent -compact "mercury"
.It "pi	ratio of circumference to diameter"
.It "c	speed of light"
.It "e	charge on an electron"
.It "g	acceleration of gravity"
.It "force	same as g"
.It "mole	Avogadro's number"
.It "water	pressure per unit height of water"
.It "mercury	pressure per unit height of mercury"
.It "au	astronomical unit"
.El
.Pp
The unit
.Dq Ic pound
is a unit of mass.
Compound names are run together
so
.Dq Ic pound force
is a unit of force.
The unit
.Dq Ic ounce
is also a unit of mass.
The fluid ounce is
.Dq Ic floz .
British units that differ from
their US counterparts are prefixed with
.Dq br ,
and currency is prefixed with its country name:
.Dq Ic belgiumfranc ,
.Dq Ic britainpound .
When searching
for a unit, if the specified string does not appear exactly as a unit
name, then
.Nm
will try to remove a trailing
.Dq s
or a trailing
.Dq es
and check again for a match.
.Ss Units file format
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
.Dq \&!
characters.
The
.Nm
program will not detect infinite loops that could be caused
by careless unit definitions.
Comments in the unit definition file
begin with a
.Dq #
or
.Dq /
character at the beginning of a line.
.Pp
Prefixes are defined in the same way as standard units, but with
a trailing dash
.Pq Dq -
at the end of the prefix name.
If a unit is not found
even after removing trailing
.Dq s
or
.Dq es ,
then it will be checked against the list of prefixes.
Prefixes will be removed until a legal
base unit is identified.
.Sh ENVIRONMENT
.Bl -tag -width PATH
.It Ev PATH
The colon-separated list of root directories at which
.Nm
tries to find
.Pa /usr/share/misc/definitions.units .
.Pp
For example if
.Ev PATH
is set to
.Dq Li /tmp:/:/usr/local ,
no
.Fl f
flags are provided, and
.Pa /usr/share/misc/definitions.units
is missing then
.Nm
tries to open the following files as the default units file:
.Pa /tmp/usr/share/misc/definitions.units ,
.Pa /usr/share/misc/definitions.units ,
and
.Pa /usr/local/usr/share/misc/definitions.units .
.El
.Sh FILES
.Bl -tag -width /usr/share/misc/definitions.units -compact
.It Pa /usr/share/misc/definitions.units
The standard units file.
.El
.Sh EXIT STATUS
.Ex -std
.Sh EXAMPLES
.Bl -tag -width 0n
.It Sy Example 1 : No Simple conversion of units
.Pp
This example shows how to do simple conversions, for example from gigabytes
to bytes:
.Bd -literal -offset 2n
.Li $ Ic units -o %0.f -t '4 gigabytes' bytes
4294967296
.Ed
.Pp
The
.Fl o Cm %0.f
part of the command is required to print the result in a non-scientific
notation (e.g, 4294967296 instead of 4.29497e+09).
.It Sy Example 2 : No Interactive usage
.Pp
Here is an example of an interactive session where the user is prompted for
units:
.Bd -literal -offset 2n
.Li You have : Ic meters
.Li You want : Ic feet
        * 3.2808399
        / 0.3048

.Li You have : Ic cm^3
.Li You want : Ic gallons
        * 0.00026417205
        / 3785.4118

.Li You have : Ic meters/s
.Li You want : Ic furlongs/fortnight
        * 6012.8848
        / 0.00016630952

.Li You have : Ic 1|2 inch
.Li You want : Ic cm
        * 1.27
        / 0.78740157

.Li You have : Ic 85 degF
.Li You want : Ic degC
        29.444444
.Ed
.It Sy Example 3 : No Difference between Do Ic \&| Dc No and Do Ic / Dc No division
.Pp
The following command shows how to convert half a meter to centimeters.
.Bd -literal -offset 2n
.Li $ Ic units '1|2 meter' cm
        * 50
        / 0.02
.Ed
.Pp
.Nm
prints the expected result because the division operator for numbers
.Pq Dq Li \&|
was used.
.Pp
Using the division operator for units
.Pq Dq Li /
would result in an error:
.Bd -literal -offset 2n
.Li $ Ic units '1/2 meter' cm
conformability error
        0.5 / m
        0.01 m
.Ed
.Pp
It is because
.Nm
interprets
.Dq Ic 1/2 meter
as
.Dq Ic 0.5/meter ,
which is not conformable to
.Dq Ic cm .
.It Sy Example 4 : No Simple units file
Here is an example of a short units file that defines some basic
units:
.Pp
.Bl -column -offset 2n -compact "minute"
.It "m	!a!"
.It "sec	!b!"
.It "micro-	1e-6"
.It "minute	60 sec"
.It "hour	60 min"
.It "inch	0.0254 m"
.It "ft	12 inches"
.It "mile	5280 ft"
.El
.It Sy Example 5 : No Viewing units and conversions of the default units file
The following shell one-liner allows the user to view the contents of the
default units file:
.Bd -literal -offset 2n
.Li $ Ic less \&"$(units -U)"
.Ed
.El
.Sh DIAGNOSTICS
.Bl -diag
.It can't find units file '%s'
The default units file is not in its default location
.Pq see Sx FILES
and it is not present in any file tree starting with their roots at directories from
.Ev PATH
.Pq see Sx ENVIRONMENT .
.It cap_rights_limit\&() failed
See
.Xr capsicum  4 .
.It conformability error
It is not possible to reduce the given units to one common unit:
they are not conformable.
Instead of a conversion,
.Nm
will display the reduced form for each provided unit:
.Bd -literal -offset 2n
.Li You have : Ic ergs/hour
.Li You want : Ic fathoms kg^2 / day
conformability error
        2.7777778e-11 kg m^2 / sec^3
        2.1166667e-05 kg^2 m / sec
.Ed
.It Could not initialize history
See
.Xr editline 3 .
.It dupstr
.Xr strdup 3
failed.
.It memory for prefixes exceeded in line %d
Over 100 prefixes were defined.
.It memory for units exceeded in line %d
Over 1000 prefixes were defined.
.It memory overflow in unit reduction
The requested conversion involves too many units
.Pq see Sx BUGS .
.It redefinition of prefix '%s' on line %d ignored
.No ""
.It redefinition of unit '%s' on line %d ignored
.No ""
.It unexpected end of prefix on line %d
.No ""
.It unexpected end of unit on line %d
.No ""
.It Units data file not found
The default units file is missing.
.It unable to enter capability mode
See
.Xr capsicum  4 .
.It unable to open units file '%s'
One of the user-specified units files cannot be opened.
.It unit reduces to zero
.No ""
.It unknown unit '%s'
The provided unit cannot be found in the units file.
.It WARNING: conversion of non-proportional quantities.
.Nm
may fail to convert
.Ar from
to
.Ar to
because the units are not proportional.
The warning is printed when a quantity is a part of the
.Ar to
argument.
It can be illustrated on an example of conversion from Fahrenheit to Celsius:
.Bd -literal -offset 2n
.Li $ Ic units \&"degF" \&"degC"
         (-> x*0.55555556g -17.777778g)
         (<- y*1.8g 32g)
.Li $ Ic units \&"degF" \&"1 degC"
WARNING: conversion of non-proportional quantities.
         (-> x*0.55555556g -17.777778g)
         (<- y*1.8g 32g)
.Li $ Ic units \&"1 degF" \&"1 degC"
WARNING: conversion of non-proportional quantities.
        -17.222222
.Ed
.El
.Sh SEE ALSO
.Xr bc 1
.Sh HISTORY
The
.Nm
first appeared in
.Nx
and was ported to
.Fx 2.2.0 .
.Pp
The manual page was significantly rewritten in
.Fx 13.0
by
.An Mateusz Piotrowski Aq Mt 0mp@FreeBSD.org .
.Sh AUTHORS
.An Adrian Mariano Aq Mt adrian@cam.cornell.edu
.Sh BUGS
The effect of including a
.Dq /
in a prefix is surprising.
.Pp
Exponents entered by the user can be only one digit.
You can work around this by multiplying several terms.
.Pp
The user must use
.Dq Ic \&|
to indicate division of numbers and
.Dq Ic /
to indicate division of symbols.
This distinction should not
be necessary.
.Pp
The program contains various arbitrary limits on the length
of the units converted and on the length of the data file.
.Pp
The program should use a hash table to store units so that
it does not take so long to load the units list and check
for duplication.
.Pp
It is not possible to convert a negative value.
.Pp
The
.Nm
program
does not handle reductions of long lists of units very well:
.Bd -literal -offset 2n
.Li $ Ic units \&"$(yes m | head -n 154)" \&"$(yes cm | head -n 154)"
        * 1e+308
        / 1e-308
.Li $ Ic units \&"$(yes m | head -n 333)" \&"$(yes cm | head -n 333)"
        * inf
        / 0
.Li $ Ic units \&"$(yes m | head -n 500)" \&"$(yes cm | head -n 500)"
units: memory overflow in unit reduction
conformability error
        1 m^500
        1 centi cm^499
.Li $ Ic units \&"$(yes m | head -n 501)" \&"$(yes cm | head -n 501)"
units: memory overflow in unit reduction
units: memory overflow in unit reduction
units: memory overflow in unit reduction
conformability error
        1 m^500
        1 centi cm^499
.Ed