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**PROGRAM:**

**NAME**

units — unit conversion and calculation program

**SYNOPSIS**

'units' [

__options__] [

__from-unit__[

__to-unit__]]

**DESCRIPTION**

The 'units' program converts quantities expressed in various systems of measurement to

their equivalents in other systems of measurement. Like many similar programs, it can

handle multiplicative scale changes. It can also handle nonlinear conversions such as

Fahrenheit to Celsius; see

__Temperature__

__Conversions__. The program can also perform

conversions from and to sums of units, such as converting between meters and feet plus

inches.

Basic operation is simple: you enter the units that you want to convert

__from__and the units

that you want to convert

__to__. You can use the program interactively with prompts, or you

can use it from the command line.

Beyond simple unit conversions, 'units' can be used as a general-purpose scientific

calculator that keeps track of units in its calculations. You can form arbitrary complex

mathematical expressions of dimensions including sums, products, quotients, powers, and

even roots of dimensions. Thus you can ensure accuracy and dimensional consistency when

working with long expressions that involve many different units that may combine in

complex ways; for an illustration, see

__Complicated__

__Unit__

__Expressions__.

The units are defined in an external data file. You can use the extensive data file that

comes with this program, or you can provide your own data file to suit your needs. You

can also use your own data file to supplement the standard data file.

You can change the default behavior of 'units' with various options given on the command

line. See

__Invoking__

__Units__for a description of the available options.

**INTERACTING**

**WITH**

**UNITS**To invoke units for interactive use, type '

__units__' at your shell prompt. The program will

print something like this:

Currency exchange rates from www.timegenie.com on 2014-03-05

2860 units, 109 prefixes, 85 nonlinear units

You have:

At the 'You have:' prompt, type the quantity and units that you are converting

__from__. For

example, if you want to convert ten meters to feet, type '

__10__

__meters__'. Next, 'units' will

print 'You want:'. You should type the units you want to convert

__to__. To convert to feet,

you would type '

__feet__'. If the 'readline' library was compiled in then

__tab__will complete

unit names. See

__Readline__

__Support__for more information about 'readline'. To quit the

program under Unix, press

__Ctrl-C__or

__Ctrl-D__. Under Windows, press

__Ctrl-C__or

__Ctrl-Z__; with

the latter, you may also need to press

__Enter__.

The result will be displayed in two ways. The first line of output, which is marked with

a '*' to indicate multiplication, gives the result of the conversion you have asked for.

The second line of output, which is marked with a '/' to indicate division, gives the

inverse of the conversion factor. If you convert 10 meters to feet, 'units' will print

* 32.808399

/ 0.03048

which tells you that 10 meters equals about 32.8 feet. The second number gives the

conversion in the opposite direction. In this case, it tells you that 1 foot is equal to

about 0.03 dekameters since the dekameter is 10 meters. It also tells you that 1/32.8 is

about 0.03.

The 'units' program prints the inverse because sometimes it is a more convenient number.

In the example above, for example, the inverse value is an exact conversion: a foot is

exactly 0.03048 dekameters. But the number given the other direction is inexact.

If you convert grains to pounds, you will see the following:

You have: grains

You want: pounds

* 0.00014285714

/ 7000

From the second line of the output you can immediately see that a grain is equal to a

seven thousandth of a pound. This is not so obvious from the first line of the output.

If you find the output format confusing, try using the '--verbose' option:

You have: grain

You want: aeginamina

grain = 0.00010416667 aeginamina

grain = (1 / 9600) aeginamina

If you request a conversion between units that measure reciprocal dimensions, then 'units'

will display the conversion results with an extra note indicating that reciprocal

conversion has been done:

You have: 6 ohms

You want: siemens

reciprocal conversion

* 0.16666667

/ 6

Reciprocal conversion can be suppressed by using the '--strict' option. As usual, use the

'--verbose' option to get more comprehensible output:

You have: tex

You want: typp

reciprocal conversion

1 / tex = 496.05465 typp

1 / tex = (1 / 0.0020159069) typp

You have: 20 mph

You want: sec/mile

reciprocal conversion

1 / 20 mph = 180 sec/mile

1 / 20 mph = (1 / 0.0055555556) sec/mile

If you enter 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

If you only want to find the reduced form or definition of a unit, simply press

__Enter__at

the 'You want:' prompt. Here is an example:

You have: jansky

You want:

Definition: fluxunit = 1e-26 W/m^2 Hz = 1e-26 kg / s^2

The output from 'units' indicates that the jansky is defined to be equal to a fluxunit

which in turn is defined to be a certain combination of watts, meters, and hertz. The

fully reduced (and in this case somewhat more cryptic) form appears on the far right.

Some named units are treated as dimensionless in some situations. These units include the

radian and steradian. These units will be treated as equal to 1 in units conversions.

Power is equal to torque times angular velocity. This conversion can only be performed if

the radian is dimensionless.

You have: (14 ft lbf) (12 radians/sec)

You want: watts

* 227.77742

/ 0.0043902509

It is also possible to compute roots and other non-integer powers of dimensionless units;

this allows computations such as the altitude of geosynchronous orbit:

You have: cuberoot(G earthmass / (circle/siderealday)^2) - earthradius

You want: miles

* 22243.267

/ 4.4957425e-05

Named dimensionless units are not treated as dimensionless in other contexts. They cannot

be used as exponents so for example, 'meter^radian' is forbidden.

If you want a list of options you can type '

__?__' at the 'You want:' prompt. The program

will display a list of named units that are conformable with the unit that you entered at

the 'You have:' prompt above. Conformable unit

__combinations__will not appear on this list.

Typing '

__help__' at either prompt displays a short help message. You can also type '

__help__'

followed by a unit name. This will invoke a pager on the units data base at the point

where that unit is defined. You can read the definition and comments that may give more

details or historical information about the unit. (You can generally quit out of the page

by pressing 'q'.)

Typing '

__search__'

__text__will display a list of all of the units whose names contain

__text__as a

substring along with their definitions. This may help in the case where you aren't sure

of the right unit name.

**USING** **UNITS** **NON-INTERACTIVELY**

**UNITS**

The 'units' program can perform units conversions non-interactively from the command line.

To do this, type the command, type the original unit expression, and type the new units

you want. If a units expression contains non-alphanumeric characters, you may need to

protect it from interpretation by the shell using single or double quote characters.

If you type

units "2 liters" quarts

then 'units' will print

* 2.1133764

/ 0.47317647

and then exit. The output tells you that 2 liters is about 2.1 quarts, or alternatively

that a quart is about 0.47 times 2 liters.

If the conversion is successful, then 'units' will return success (zero) to the calling

environment. If you enter non-conformable units then 'units' will print a message giving

the reduced form of each unit and it will return failure (nonzero) to the calling

environment.

When you invoke 'units' with only one argument, it will print out the definition of the

specified unit. It will return failure if the unit is not defined and success if the unit

is defined.

**UNIT** **DEFINITIONS**

The conversion information is read from a units data file that is called

'definitions.units' and is usually located in the '/usr/share/units' directory. If you

invoke 'units' with the '-V' option, it will print the location of this file. The default

file includes definitions for all familiar units, abbreviations and metric prefixes. It

also includes many obscure or archaic units.

Many constants of nature are defined, including these:

pi ratio of circumference to diameter

c speed of light

e charge on an electron

force acceleration of gravity

mole Avogadro's number

water pressure per unit height of water

Hg pressure per unit height of mercury

au astronomical unit

k Boltzman's constant

mu0 permeability of vacuum

epsilon0 permittivity of vacuum

G Gravitational constant

mach speed of sound

The standard data file includes atomic masses for all of the elements and numerous other

constants. Also included are the densities of various ingredients used in baking so that

'2 cups flour_sifted' can be converted to 'grams'. This is not an exhaustive list.

Consult the units data file to see the complete list, or to see the definitions that are

used.

The 'pound' is a unit of mass. To get force, multiply by the force conversion unit

'force' or use the shorthand 'lbf'. (Note that 'g' is already taken as the standard

abbreviation for the gram.) The unit 'ounce' is also a unit of mass. The fluid ounce is

'fluidounce' or 'floz'. When British capacity units differ from their US counterparts,

such as the British Imperial gallon, the unit is defined both ways with 'br' and 'us'

prefixes. Your locale settings will determine the value of the unprefixed unit. 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', 'es'. Next units will replace

a trailing 'ies' with 'y'. If that fails, 'units' will check for a prefix. The database

includes all of the standard metric prefixes. Only one prefix is permitted per unit, so

'micromicrofarad' will fail. However, prefixes can appear alone with no unit following

them, so 'micro*microfarad' will work, as will 'micro microfarad'.

To find out which units and prefixes are available, read the standard units data file,

which is extensively annotated.

**English**

**Customary**

**Units**

English customary units differ in various ways in different regions. In Britain a complex

system of volume measurements featured different gallons for different materials such as a

wine gallon and ale gallon that different by twenty percent. This complexity was swept

away in 1824 by a reform that created an entirely new gallon, the British Imperial gallon

defined as the volume occupied by ten pounds of water. Meanwhile in the USA the gallon is

derived from the 1707 Winchester wine gallon, which is 231 cubic inches. These gallons

differ by about twenty percent. By default if 'units' runs in the 'en_GB' locale you will

get the British volume measures. If it runs in the 'en_US' locale you will get the US

volume measures. In other locales the default values are the US definitions. If you wish

to force different definitions then set the environment variable 'UNITS_ENGLISH' to either

'US' or 'GB' to set the desired definitions independent of the locale.

Before 1959, the value of a yard (and other units of measure defined in terms of it)

differed slightly among English-speaking countries. In 1959, Australia, Canada, New

Zealand, the United Kingdom, the United States, and South Africa adopted the Canadian

value of 1 yard = 0.9144 m (exactly), which was approximately halfway between the values

used by the UK and the US; it had the additional advantage of making 1 inch = 2.54 cm

(exactly). This new standard was termed the

__International__

__Yard__. Australia, Canada, and

the UK then defined all customary lengths in terms of the International Yard (Australia

did not define the furlong or rod); because many US land surveys were in terms of the

pre-1959 units, the US continued to define customary surveyors' units (furlong, chain,

rod, and link) in terms of the previous value for the foot, which was termed the

__US__

__survey__

__foot__. The US defined a

__US__

__survey__

__mile__as 5280 US survey feet, and defined a

__statute__

__mile__

as a US survey mile. The US values for these units differ from the international values

by about 2 ppm.

The 'units' program uses the international values for these units; the US values can be

obtained by using either the 'US' or the 'survey' prefix. In either case, the simple

familiar relationships among the units are maintained, e.g., 1 'furlong' = 660 'ft', and 1

'USfurlong' = 660 'USft', though the metric equivalents differ slightly between the two

cases. The 'US' prefix or the 'survey' prefix can also be used to obtain the US survey

mile and the value of the US yard prior to 1959, e.g., 'USmile' or 'surveymile' (but

__not__

'USsurveymile'). To get the US value of the statute mile, use either 'USstatutemile' or

'USmile'.

Except for distances that extend over hundreds of miles (such as in the US State Plane

Coordinate System), the differences in the miles are usually insignificant:

You have: 100 surveymile - 100 mile

You want: inch

* 12.672025

/ 0.078913984

The pre-1959 UK values for these units can be obtained with the prefix 'UK'.

In the US, the acre is officially defined in terms of the US survey foot, but 'units' uses

a definition based on the international foot. If you want the official US acre use

'USacre' and similarly use 'USacrefoot' for the official US version of that unit. The

difference between these units is about 4 parts per million.

**UNIT** **EXPRESSIONS**

**Operators**

You can enter more complicated units by combining units with operations such as

multiplication, division, powers, addition, subtraction, and parentheses for grouping.

You can use the customary symbols for these operators when 'units' is invoked with its

default options. Additionally, 'units' supports some extensions, including high priority

multiplication using a space, and a high priority numerical division operator ('|') that

can simplify some expressions.

You multiply units using a space or an asterisk ('*'). The next example shows both forms:

You have: arabicfoot * arabictradepound * force

You want: ft lbf

* 0.7296

/ 1.370614

You can divide units using the slash ('/') or with 'per':

You have: furlongs per fortnight

You want: m/s

* 0.00016630986

/ 6012.8727

You can use parentheses for grouping:

You have: (1/2) kg / (kg/meter)

You want: league

* 0.00010356166

/ 9656.0833

Multiplication using a space has a higher precedence than division using a slash and is

evaluated left to right; in effect, the first '/' character marks the beginning of the

denominator of a unit expression. This makes it simple to enter a quotient with several

terms in the denominator: 'J / mol K'. The '*' and '/' operators have the same

precedence, and are evaluated left to right; if you multiply with '*', you must group the

terms in the denominator with parentheses: 'J / (mol * K)'.

The higher precedence of the space operator may not always be advantageous. For example,

'm/s s/day' is equivalent to 'm / s s day' and has dimensions of length per time cubed.

Similarly, '1/2 meter' refers to a unit of reciprocal length equivalent to 0.5/meter,

perhaps not what you would intend if you entered that expression. The get a half meter

you would need to use parentheses: '(1/2) meter'. The '*' operator is convenient for

multiplying a sequence of quotients. For example, 'm/s * s/day' is equivalent to 'm/day'.

Similarly, you could write '1/2 * meter' to get half a meter.

The 'units' program supports another option for numerical fractions: you can indicate

division of

__numbers__with the vertical bar ('|'), so if you wanted half a meter you could

write '1|2 meter'. You cannot use the vertical bar to indicate division of non-numerical

units (e.g., 'm|s' results in an error message).

Powers of units can be specified using the '^' character, as shown in the following

example, or by simple concatenation of a unit and its exponent: 'cm3' is equivalent to

'cm^3'; if the exponent is more than one digit, the '^' is required. You can also use

'**' as an exponent operator.

You have: cm^3

You want: gallons

* 0.00026417205

/ 3785.4118

Concatenation only works with a single unit name: if you write '(m/s)2', 'units' will

treat it as multiplication by 2. When a unit includes a prefix, exponent operators apply

to the combination, so 'centimeter3' gives cubic centimeters. If you separate the prefix

from the unit with any multiplication operator (e.g., 'centi meter^3'), the prefix is

treated as a separate unit, so the exponent applies only to the unit without the prefix.

The second example is equivalent to 'centi * (meter^3)', and gives a hundredth of a cubic

meter, not a cubic centimeter. The 'units' program is limited internally to products of

99 units; accordingly, expressions like 'meter^100' or 'joule^34' (represented internally

as 'kg^34 m^68 / s^68') will fail.

The '|' operator has the highest precedence, so you can write the square root of two

thirds as '2|3^1|2'. The '^' operator has the second highest precedence, and is evaluated

right to left, as usual:

You have: 5 * 2^3^2

You want:

Definition: 2560

With a dimensionless base unit, any dimensionless exponent is meaningful (e.g.,

'pi^exp(2.371)'). Even though angle is sometimes treated as dimensionless, exponents

cannot have dimensions of angle:

You have: 2^radian

^

Exponent not dimensionless

If the base unit is not dimensionless, the exponent must be a rational number

__p__/

__q__, and the

dimension of the unit must be a power of

__q__, so 'gallon^2|3' works but 'acre^2|3' fails.

An exponent using the slash ('/') operator (e.g., 'gallon^(2/3)') is also acceptable; the

parentheses are needed because the precedence of '^' is higher than that of '/'. Since

'units' cannot represent dimensions with exponents greater than 99, a fully reduced

exponent must have

__q__< 100. When raising a non-dimensionless unit to a power, 'units'

attempts to convert a decimal exponent to a rational number with

__q__< 100. If this is not

possible 'units' displays an error message:

You have: ft^1.234

Base unit not dimensionless; rational exponent required

A decimal exponent must match its rational representation to machine precision, so

'acre^1.5' works but 'gallon^0.666' does not.

**Sums**

**and**

**Differences**

**of**

**Units**

You may sometimes want to add values of different units that are outside the SI. You may

also wish to use 'units' as a calculator that keeps track of units. Sums of conformable

units are written with the '+' character, and differences with the '-' character.

You have: 2 hours + 23 minutes + 32 seconds

You want: seconds

* 8612

/ 0.00011611705

You have: 12 ft + 3 in

You want: cm

* 373.38

/ 0.0026782366

You have: 2 btu + 450 ft lbf

You want: btu

* 2.5782804

/ 0.38785542

The expressions that are added or subtracted must reduce to identical expressions in

primitive units, or an error message will be displayed:

You have: 12 printerspoint - 4 heredium

^

Illegal sum of non-conformable units

As usual, the precedence for '+' and '-' is lower than that of the other operators. A

fractional quantity such as 2 1/2 cups can be given as '(2+1|2) cups'; the parentheses are

necessary because multiplication has higher precedence than addition. If you omit the

parentheses, 'units' attempts to add '2' and '1|2 cups', and you get an error message:

You have: 2+1|2 cups

^

Illegal sum or difference of non-conformable units

The expression could also be correctly written as '(2+1/2) cups'. If you write '2 1|2

cups' the space is interpreted as

__multiplication__so the result is the same as '1 cup'.

The '+' and '-' characters sometimes appears in exponents like '3.43e+8'. This leads to

an ambiguity in an expression like '3e+2 yC'. The unit 'e' is a small unit of charge, so

this can be regarded as equivalent to '(3e+2) yC' or '(3 e)+(2 yC)'. This ambiguity is

resolved by always interpreting '+' and '-' as part of an exponent if possible.

**Numbers**

**as**

**Units**

For 'units', numbers are just another kind of unit. They can appear as many times as you

like and in any order in a unit expression. For example, to find the volume of a box that

is 2 ft by 3 ft by 12 ft in steres, you could do the following:

You have: 2 ft 3 ft 12 ft

You want: stere

* 2.038813

/ 0.49048148

You have: $ 5 / yard

You want: cents / inch

* 13.888889

/ 0.072

And the second example shows how the dollar sign in the units conversion can precede the

five. Be careful: 'units' will interpret '$5' with no space as equivalent to 'dollar^5'.

**Built-in**

**Functions**

Several built-in functions are provided: 'sin', 'cos', 'tan', 'ln', 'log', 'log2', 'exp',

'acos', 'atan' and 'asin'. The 'sin', 'cos', and 'tan' functions require either a

dimensionless argument or an argument with dimensions of angle.

You have: sin(30 degrees)

You want:

Definition: 0.5

You have: sin(pi/2)

You want:

Definition: 1

You have: sin(3 kg)

^

Unit not dimensionless

The other functions on the list require dimensionless arguments. The inverse

trigonometric functions return arguments with dimensions of angle.

If you wish to take roots of units, you may use the 'sqrt' or 'cuberoot' functions. These

functions require that the argument have the appropriate root. You can obtain higher

roots by using fractional exponents:

You have: sqrt(acre)

You want: feet

* 208.71074

/ 0.0047913202

You have: (400 W/m^2 / stefanboltzmann)^(1/4)

You have:

Definition: 289.80882 K

You have: cuberoot(hectare)

^

Unit not a root

**Previous**

**Result**

You can insert the result of the previous conversion using the underscore ('_'). It is

useful when you want to convert the same input to several different units, for example

You have: 2.3 tonrefrigeration

You want: btu/hr

* 27600

/ 3.6231884e-005

You have: _

You want: kW

* 8.0887615

/ 0.12362832

Suppose you want to do some deep frying that requires an oil depth of 2 inches. You have

1/2 gallon of oil, and want to know the largest-diameter pan that will maintain the

required depth. The nonlinear unit 'circlearea' gives the

__radius__of the circle (see

__Other__

__Nonlinear__

__Units__, for a more detailed description) in SI units; you want the

__diameter__in

__inches__:

You have: 1|2 gallon / 2 in

You want: circlearea

0.10890173 m

You have: 2 _

You want: in

* 8.5749393

/ 0.1166189

In most cases, surrounding white space is optional, so the previous example could have

used '2_'. If '_' follows a non-numerical unit symbol, however, the space is required:

You have: m_

^

Parse error

When '_' is followed by a digit, the operation is multiplication rather than

exponentiation, so that '_2', is equivalent to '_ * 2' rather than '_^2'.

You can use the '_' symbol any number of times; for example,

You have: m

You want:

Definition: 1 m

You have: _ _

You want:

Definition: 1 m^2

Using '_' before a conversion has been performed (e.g., immediately after invocation)

generates an error:

You have: _

^

No previous result; '_' not set

Accordingly, '_' serves no purpose when 'units' is invoked non-interactively.

If 'units' is invoked with the '--verbose' option (see

__Invoking__

__Units__), the value of '_'

is not expanded:

You have: mile

You want: ft

mile = 5280 ft

mile = (1 / 0.00018939394) ft

You have: _

You want: m

_ = 1609.344 m

_ = (1 / 0.00062137119) m

You can give '_' at the 'You want:' prompt, but it usually is not very useful.

**Complicated**

**Unit**

**Expressions**

The 'units' program is especially helpful in ensuring accuracy and dimensional consistency

when converting lengthy unit expressions. For example, one form of the Darcy-Weisbach

fluid-flow equation is

Delta

__P__= (8 / pi)^2 (rho

__fLQ__^2) /

__d__^5,

where Delta

__P__is the pressure drop, rho is the mass density,

__f__is the (dimensionless)

friction factor,

__L__is the length of the pipe,

__Q__is the volumetric flow rate, and

__d__is the

pipe diameter. It might be desired to have the equation in the form

Delta

__P__= A1 rho

__fLQ__^2 /

__d__^5

that accepted the user's normal units; for typical units used in the US, the required

conversion could be something like

You have: (8/pi^2)(lbm/ft^3)ft(ft^3/s)^2(1/in^5)

You want: psi

* 43.533969

/ 0.022970568

The parentheses allow individual terms in the expression to be entered naturally, as they

might be read from the formula. Alternatively, the multiplication could be done with the

'*' rather than a space; then parentheses are needed only around 'ft^3/s' because of its

exponent:

You have: 8/pi^2 * lbm/ft^3 * ft * (ft^3/s)^2 /in^5

You want: psi

* 43.533969

/ 0.022970568

Without parentheses, and using spaces for multiplication, the previous conversion would

need to be entered as

You have: 8 lb ft ft^3 ft^3 / pi^2 ft^3 s^2 in^5

You want: psi

* 43.533969

/ 0.022970568

**Backwards**

**Compatibility:**

'*' and '-' The original 'units' assigned multiplication a higher precedence than division

using the slash. This differs from the usual precedence rules, which give multiplication

and division equal precedence, and can be confusing for people who think of units as a

calculator.

The star operator ('*') included in this 'units' program has, by default, the same

precedence as division, and hence follows the usual precedence rules. For backwards

compatibility you can invoke 'units' with the '--oldstar' option. Then '*' has a higher

precedence than division, and the same precedence as multiplication using the space.

Historically, the hyphen ('-') has been used in technical publications to indicate

products of units, and the original 'units' program treated it as a multiplication

operator. Because 'units' provides several other ways to obtain unit products, and

because '-' is a subtraction operator in general algebraic expressions, 'units' treats the

binary '-' as a subtraction operator by default. For backwards compatibility use the

'--product' option, which causes 'units' to treat the binary '-' operator as a product

operator. When '-' is a multiplication operator it has the same precedence as

multiplication with a space, giving it a higher precedence than division.

When '-' is used as a unary operator it negates its operand. Regardless of the 'units'

options, if '-' appears after '(' or after '+' then it will act as a negation operator.

So you can always compute 20 degrees minus 12 minutes by entering '20 degrees +

-12 arcmin'. You must use this construction when you define new units because you cannot

know what options will be in force when your definition is processed.

**NONLINEAR** **UNIT** **CONVERSIONS**

Nonlinear units are represented using functional notation. They make possible nonlinear

unit conversions such as temperature.

**Temperature**

**Conversions**

Conversions between temperatures are different from linear conversions between temperature

__increments__—see the example below. The absolute temperature conversions are handled by

units starting with 'temp', and you must use functional notation. The temperature-

increment conversions are done using units starting with 'deg' and they do not require

functional notation.

You have: tempF(45)

You want: tempC

7.2222222

You have: 45 degF

You want: degC

* 25

/ 0.04

Think of 'tempF(

__x__)' not as a function but as a notation that indicates that

__x__should have

units of 'tempF' attached to it. See

__Defining__

__Nonlinear__

__Units__. The first conversion

shows that if it's 45 degrees Fahrenheit outside, it's 7.2 degrees Celsius. The second

conversion indicates that a change of 45 degrees Fahrenheit corresponds to a change of 25

degrees Celsius. The conversion from 'tempF(

__x__)' is to absolute temperature, so that

You have: tempF(45)

You want: degR

* 504.67

/ 0.0019814929

gives the same result as

You have: tempF(45)

You want: tempR

* 504.67

/ 0.0019814929

But if you convert 'tempF(

__x__)' to 'degC', the output is probably not what you expect:

You have: tempF(45)

You want: degC

* 280.37222

/ 0.0035666871

The result is the temperature in K, because 'degC' is defined as 'K', the Kelvin. For

consistent results, use the 'temp

__X__' units when converting to a temperature rather than

converting a temperature increment.

The 'tempC()' and 'tempF()' definitions are limited to positive absolute temperatures, and

giving a value that would result in a negative absolute temperature generates an error

message:

You have: tempC(-275)

^

Argument of function outside domain

^

**Other**

**Nonlinear**

**Units**

Some other examples of nonlinear units are numerous different ring sizes and wire gauges,

the grit sizes used for abrasives, the decibel scale, shoe size, scales for the density of

sugar (e.g., baume). The standard data file also supplies units for computing the area of

a circle and the volume of a sphere. See the standard units data file for more details.

Wire gauges with multiple zeroes are signified using negative numbers where two zeroes is

'-1'. Alternatively, you can use the synonyms 'g00', 'g000', and so on that are defined

in the standard units data file.

You have: wiregauge(11)

You want: inches

* 0.090742002

/ 11.020255

You have: brwiregauge(g00)

You want: inches

* 0.348

/ 2.8735632

You have: 1 mm

You want: wiregauge

18.201919

You have: grit_P(600)

You want: grit_ansicoated

342.76923

The last example shows the conversion from P graded sand paper, which is the European

standard and may be marked ``P600'' on the back, to the USA standard.

You can compute the area of a circle using the nonlinear unit, 'circlearea'. You can also

do this using the circularinch or circleinch. The next example shows two ways to compute

the area of a circle with a five inch radius and one way to compute the volume of a sphere

with a radius of one meter.

You have: circlearea(5 in)

You want: in2

* 78.539816

/ 0.012732395

You have: 10^2 circleinch

You want: in2

* 78.539816

/ 0.012732395

You have: spherevol(meter)

You want: ft3

* 147.92573

/ 0.0067601492

The inverse of a nonlinear conversion is indicated by prefixing a tilde ('~') to the

nonlinear unit name:

You have: ~wiregauge(0.090742002 inches)

You want:

Definition: 11

You can give a nonlinear unit definition without an argument or parentheses, and press

__Enter__at the 'You want:' prompt to get the definition of a nonlinear unit; if the

definition is not valid for all real numbers, the range of validity is also given. If the

definition requires specific units this information is also displayed:

You have: tempC

Definition: tempC(x) = x K + stdtemp

defined for x >= -273.15

You have: ~tempC

Definition: ~tempC(tempC) = (tempC +(-stdtemp))/K

defined for tempC >= 0 K

You have: circlearea

Definition: circlearea(r) = pi r^2

r has units m

To see the definition of the inverse use the '~' notation. In this case the parameter in

the functional definition will usually be the name of the unit. Note that the inverse for

'tempC' shows that it requires units of 'K' in the specification of the allowed range of

values. Nonlinear unit conversions are described in more detail in

__Defining__

__Nonlinear__

__Units__.

**UNIT** **LISTS:** **CONVERSION** **TO** **SUMS** **OF** **UNITS**

Outside of the SI, it is sometimes desirable to convert a single unit to a sum of units—

for example, feet to feet plus inches. The conversion

__from__sums of units was described in

__Sums__

__and__

__Differences__

__of__

__Units__, and is a simple matter of adding the units with the '+'

sign:

You have: 12 ft + 3 in + 3|8 in

You want: ft

* 12.28125

/ 0.081424936

Although you can similarly write a sum of units to convert

__to__, the result will not be the

conversion to the units in the sum, but rather the conversion to the particular sum that

you have entered:

You have: 12.28125 ft

You want: ft + in + 1|8 in

* 11.228571

/ 0.089058524

The unit expression given at the 'You want:' prompt is equivalent to asking for conversion

to multiples of '1 ft + 1 in + 1|8 in', which is 1.09375 ft, so the conversion in the

previous example is equivalent to

You have: 12.28125 ft

You want: 1.09375 ft

* 11.228571

/ 0.089058524

In converting to a sum of units like miles, feet and inches, you typically want the

largest integral value for the first unit, followed by the largest integral value for the

next, and the remainder converted to the last unit. You can do this conversion easily

with 'units' using a special syntax for lists of units. You must list the desired units

in order from largest to smallest, separated by the semicolon (';') character:

You have: 12.28125 ft

You want: ft;in;1|8 in

12 ft + 3 in + 3|8 in

The conversion always gives integer coefficients on the units in the list, except possibly

the last unit when the conversion is not exact:

You have: 12.28126 ft

You want: ft;in;1|8 in

12 ft + 3 in + 3.00096 * 1|8 in

The order in which you list the units is important:

You have: 3 kg

You want: oz;lb

105 oz + 0.051367866 lb

You have: 3 kg

You want: lb;oz

6 lb + 9.8218858 oz

Listing ounces before pounds produces a technically correct result, but not a very useful

one. You must list the units in descending order of size in order to get the most useful

result.

Ending a unit list with the separator ';' has the same effect as repeating the last unit

on the list, so 'ft;in;1|8 in;' is equivalent to 'ft;in;1|8 in;1|8 in'. With the example

above, this gives

You have: 12.28126 ft

You want: ft;in;1|8 in;

12 ft + 3 in + 3|8 in + 0.00096 * 1|8 in

in effect separating the integer and fractional parts of the coefficient for the last

unit. If you instead prefer to round the last coefficient to an integer you can do this

with the '--round' ('-r') option. With the previous example, the result is

You have: 12.28126 ft

You want: ft;in;1|8 in

12 ft + 3 in + 3|8 in (rounded down to nearest 1|8 in)

When you use the '-r' option, repeating the last unit on the list has no effect (e.g.,

'ft;in;1|8 in;1|8 in' is equivalent to 'ft;in;1|8 in'), and hence neither does ending a

list with a ';'. With a single unit and the '-r' option, a terminal ';'

__does__have an

effect: it causes 'units' to treat the single unit as a list and produce a rounded value

for the single unit. Without the extra ';', the '-r' option has no effect on single unit

conversions. This example shows the output using the '-r' option:

You have: 12.28126 ft

You want: in

* 147.37512

/ 0.0067854058

You have: 12.28126 ft

You want: in;

147 in (rounded down to nearest in)

Each unit that appears in the list must be conformable with the first unit on the list,

and of course the listed units must also be conformable with the unit that you enter at

the 'You have:' prompt.

You have: meter

You want: ft;kg

^

conformability error

ft = 0.3048 m

kg = 1 kg

You have: meter

You want: lb;oz

conformability error

1 m

0.45359237 kg

In the first case, 'units' reports the disagreement between units appearing on the list.

In the second case, 'units' reports disagreement between the unit you entered and the

desired conversion. This conformability error is based on the first unit on the unit

list.

Other common candidates for conversion to sums of units are angles and time:

You have: 23.437754 deg

You want; deg;arcmin;arcsec

23 deg + 26 arcmin + 15.9144 arcsec

You have: 7.2319 hr

You want: hr;min;sec

7 hr + 13 min + 54.84 sec

In North America, recipes for cooking typically measure ingredients by volume, and use

units that are not always convenient multiples of each other. Suppose that you have a

recipe for 6 and you wish to make a portion for 1. If the recipe calls for 2 1/2 cups of

an ingredient, you might wish to know the measurements in terms of measuring devices you

have available, you could use 'units' and enter

You have: (2+1|2) cup / 6

You want: cup;1|2 cup;1|3 cup;1|4 cup;tbsp;tsp;1|2 tsp;1|4 tsp

1|3 cup + 1 tbsp + 1 tsp

By default, if a unit in a list begins with fraction of the form 1|

__x__and its multiplier is

an integer, the fraction is given as the product of the multiplier and the numerator; for

example,

You have: 12.28125 ft

You want: ft;in;1|8 in;

12 ft + 3 in + 3|8 in

In many cases, such as the example above, this is what is wanted, but sometimes it is not.

For example, a cooking recipe for 6 might call for 5 1/4 cup of an ingredient, but you

want a portion for 2, and your 1-cup measure is not available; you might try

You have: (5+1|4) cup / 3

You want: 1|2 cup;1|3 cup;1|4 cup

3|2 cup + 1|4 cup

This result might be fine for a baker who has a 1 1/2-cup measure (and recognizes the

equivalence), but it may not be as useful to someone with more limited set of measures,

who does want to do additional calculations, and only wants to know ``How many 1/2-cup

measures to I need to add?'' After all, that's what was actually asked. With the

'--show-factor' option, the factor will not be combined with a unity numerator, so that

you get

You have: (5+1|4) cup / 3

You want: 1|2 cup;1|3 cup;1|4 cup

3 * 1|2 cup + 1|4 cup

A user-specified fractional unit with a numerator other than 1 is never overridden,

however—if a unit list specifies '3|4 cup;1|2 cup', a result equivalent to 1 1/2 cups will

always be shown as '2 * 3|4 cup' whether or not the '--show-factor' option is given.

Some applications for unit lists may be less obvious. Suppose that you have a postal

scale and wish to ensure that it's accurate at 1 oz, but have only metric calibration

weights. You might try

You have: 1 oz

You want: 100 g;50 g; 20 g;10 g;5 g;2 g;1 g;

20 g + 5 g + 2 g + 1 g + 0.34952312 * 1 g

You might then place one each of the 20 g, 5 g, 2 g, and 1 g weights on the scale and hope

that it indicates close to

You have: 20 g + 5 g + 2 g + 1 g

You want: oz;

0.98767093 oz

Appending ';' to 'oz' forces a one-line display that includes the unit; here the integer

part of the result is zero, so it is not displayed.

A unit list such as

cup;1|2 cup;1|3 cup;1|4 cup;tbsp;tsp;1|2 tsp;1|4 tsp

can be tedious to enter. The 'units' program provides shorthand names for some common

combinations:

hms hours, minutes, seconds

dms angle: degrees, minutes, seconds

time years, days, hours, minutes and seconds

usvol US cooking volume: cups and smaller

Using these shorthands, or

__unit__

__list__

__aliases__, you can do the following conversions:

You have: anomalisticyear

You want: time

1 year + 25 min + 3.4653216 sec

You have: 1|6 cup

You want: usvol

2 tbsp + 2 tsp

You cannot combine a unit list alias with other units: it must appear alone at the

'You want:' prompt.

You can display the definition of a unit list alias by entering it at the 'You have:'

prompt:

You have: dms

Definition: unit list, deg;arcmin;arcsec

When you specify compact output with '--compact', '--terse' or '-t' and perform conversion

to a unit list, 'units' lists the conversion factors for each unit in the list, separated

by semicolons.

You have: year

You want: day;min;sec

365;348;45.974678

Unlike the case of regular output, zeros

__are__included in this output list:

You have: liter

You want: cup;1|2 cup;1|4 cup;tbsp

4;0;0;3.6280454

**LOGGING** **CALCULATIONS**

The '--log' option allows you to save the results of calculations in a file; this can be

useful if you need a permanent record of your work. For example, the fluid-flow

conversion in

__Complicated__

__Unit__

__Expressions__, is lengthy, and if you were to use it in

designing a piping system, you might want a record of it for the project file. If the

interactive session

# Conversion factor A1 for pressure drop

# dP = A1 rho f L Q^2/d^5

You have: (8/pi^2) (lbm/ft^3)ft(ft^3/s)^2(1/in^5) # Input units

You want: psi

* 43.533969

/ 0.022970568

were logged, the log file would contain

### Log started Fri Oct 02 15:55:35 2015

# Conversion factor A1 for pressure drop

# dP = A1 rho f L Q^2/d^5

From: (8/pi^2) (lbm/ft^3)ft(ft^3/s)^2(1/in^5) # Input units

To: psi

* 43.533969

/ 0.022970568

The time is written to the log file when the file is opened.

The use of comments can help clarify the meaning of calculations for the log. The log

includes conformability errors between the units at the 'You have:' and 'You want:'

prompts, but not other errors, including lack of conformability of items in sums or

differences or among items in a unit list. For example, a conversion between zenith angle

and elevation angle could involve

You have: 90 deg - (5 deg + 22 min + 9 sec)

^

Illegal sum or difference of non-conformable units

You have: 90 deg - (5 deg + 22 arcmin + 9 arcsec)

You want: dms

84 deg + 37 arcmin + 51 arcsec

You have: _

You want: deg

* 84.630833

/ 0.011816024

You have:

The log file would contain

From: 90 deg - (5 deg + 22 arcmin + 9 arcsec)

To: deg;arcmin;arcsec

84 deg + 37 arcmin + 51 arcsec

From: _

To: deg

* 84.630833

/ 0.011816024

The initial entry error (forgetting that minutes have dimension of time, and that

arcminutes must be used for dimensions of angle) does not appear in the output. When

converting to a unit list alias, 'units' expands the alias in the log file.

The 'From:' and 'To:' tags are written to the log file even if the '--quiet' option is

given. If the log file exists when 'units' is invoked, the new results are appended to

the log file. The time is written to the log file each time the file is opened. The

'--log' option is ignored when 'units' is used non-interactively.

**INVOKING**

**UNITS**You invoke 'units' like this:

units [

__options__] [

__from-unit__[

__to-unit__]]

If the

__from-unit__and

__to-unit__are omitted, the program will use interactive prompts to

determine which conversions to perform. See

__Interactive__

__Use__. If both

__from-unit__and

__to-__

__unit__are given, 'units' will print the result of that single conversion and then exit. If

only

__from-unit__appears on the command line, 'units' will display the definition of that

unit and exit. Units specified on the command line may need to be quoted to protect them

from shell interpretation and to group them into two arguments. See

__Command__

__Line__

__Use__.

The default behavior of 'units' can be changed by various options given on the command

line. In most cases, the options may be given in either short form (a single '-' followed

by a single character) or long form ('--' followed by a word or hyphen-separated words).

Short-form options are cryptic but require less typing; long-form options require more

typing but are more explanatory and may be more mnemonic. With long-form options you need

only enter sufficient characters to uniquely identify the option to the program. For

example, '--out %f' works, but '--o %f' fails because 'units' has other long options

beginning with 'o'. However, '--q' works because '--quiet' is the only long option

beginning with 'q'.

Some options require arguments to specify a value (e.g., '-d 12' or '--digits 12').

Short-form options that do not take arguments may be concatenated (e.g., '-erS' is

equivalent to '-e -r -S'); the last option in such a list may be one that takes an

argument (e.g., '-ed 12'). With short-form options, the space between an option and its

argument is optional (e.g., '-d12' is equivalent to '-d 12'). Long-form options may not

be concatenated, and the space between a long-form option and its argument is required.

Short-form and long-form options may be intermixed on the command line. Options may be

given in any order, but when incompatible options (e.g., '--output-format' and

'--exponential') are given in combination, behavior is controlled by the last option

given. For example, '-o%.12f -e' gives exponential format with the default eight

significant digits).

The following options are available:

**-c**,

**--check**

Check that all units and prefixes defined in the units data file reduce to

primitive units. Print a list of all units that cannot be reduced. Also display

some other diagnostics about suspicious definitions in the units data file. Only

definitions active in the current locale are checked. You should always run

'units' with this option after modifying a units data file.

**--check-verbose**,

**--verbose-check**

Like the '--check' option, this option prints a list of units that cannot be

reduced. But to help find unit definitions that cause endless loops, it lists the

units as they are checked. If 'units' hangs, then the last unit to be printed has

a bad definition. Only definitions active in the current locale are checked.

**-d**

__ndigits__,

**--digits**

__ndigits__

Set the number of significant digits in the output to the value specified (which

must be greater than zero). For example, '-d 12' sets the number of significant

digits to 12. With exponential output 'units' displays one digit to the left of

the decimal point and eleven digits to the right of the decimal point. On most

systems, the maximum number of internally meaningful digits is 15; if you specify a

greater number than your system's maximum, 'units' will print a warning and set the

number to the largest meaningful value. To directly set the maximum value, give an

argument of 'max' (e.g., '-d max'). Be aware, of course, that ``significant'' here

refers only to the

__display__of numbers; if results depend on physical constants not

known to this precision, the physically meaningful precision may be less than that

shown. The '--digits' option conflicts with the '--output-format' option.

**-e**,

**--exponential**

Set the numeric output format to exponential (i.e., scientific notation), like that

used in the Unix 'units' program. The default precision is eight significant

digits (seven digits to the right of the decimal point); this can be changed with

the '--digits' option. The '--exponential' option conflicts with the '--output-

format' option.

**-o**

__format__,

**--output-format**

__format__

This option affords complete control over the numeric output format using the

specified

__format__. The format is a single floating point numeric format for the

'printf()' function in the C programming language. All compilers support the

format types 'g' and 'G' to specify significant digits, 'e' and 'E' for scientific

notation, and 'f' for fixed-point decimal. The ISO C99 standard introduced the 'F'

type for fixed-point decimal and the 'a' and 'A' types for hexadecimal floating

point; these types are allowed with compilers that support them. The default

format is '%.8g'; for greater precision, you could specify '-o %.15g'. See

__Numeric__

__Output__

__Format__and the documentation for 'printf()' for more detailed descriptions

of the format specification. The '--output-format' option affords the greatest

control of the output appearance, but requires at least rudimentary knowledge of

the 'printf()' format syntax. If you don't want to bother with the 'printf()'

syntax, you can specify greater precision more simply with the '--digits' option or

select exponential format with '--exponential'. The '--output-format' option is

incompatible with the '--exponential' and '--digits' options.

**-f**

__filename__,

**--file**

__filename__

Instruct 'units' to load the units file

__filename__. You can specify up to 25 units

files on the command line. When you use this option, 'units' will load

__only__the

files you list on the command line; it will not load the standard file or your

personal units file unless you explicitly list them. If

__filename__is the empty

string ('-f ""'), the default units file (or that specified by 'UNITSFILE') will be

loaded in addition to any others specified with '-f'.

**-L**

__logfile__,

**--log**

__logfile__

Save the results of calculations in the file

__logfile__; this can be useful if it is

important to have a record of unit conversions or other calculations that are to be

used extensively or in a critical activity such as a program or design project. If

__logfile__exits, the new results are appended to the file. This option is ignored

when 'units' is used non-interactively. See

__Logging__

__Calculations__for a more

detailed description and some examples.

**-H**

__filename__,

**--history**

__filename__

Instruct 'units' to save history to

__filename__, so that a record of your commands is

available for retrieval across different 'units' invocations. To prevent the

history from being saved set

__filename__to the empty string ('-H ""'). This option

has no effect if readline is not available.

**-h**,

**--help**

Print out a summary of the options for 'units'.

**-m**,

**--minus**

Causes '-' to be interpreted as a subtraction operator. This is the default

behavior.

**-p**,

**--product**

Causes '-' to be interpreted as a multiplication operator when it has two operands.

It will act as a negation operator when it has only one operand: '(-3)'. By

default '-' is treated as a subtraction operator.

**--oldstar**

Causes '*' to have the old-style precedence, higher than the precedence of division

so that '1/2*3' will equal '1/6'.

**--newstar**

Forces '*' to have the new (default) precedence that follows the usual rules of

algebra: the precedence of '*' is the same as the precedence of '/', so that

'1/2*3' will equal '3/2'.

**--compact**

Give compact output featuring only the conversion factor. This turns off the

'--verbose' option.

**-q**,

**--quiet**,

**--silent**

Suppress prompting of the user for units and the display of statistics about the

number of units loaded.

**-n**,

**--nolists**

Disable conversion to unit lists.

**-r**,

**--round**

When converting to a combination of units given by a unit list, round the value of

the last unit in the list to the nearest integer.

**-S**,

**--show-factor**

When converting to a combination of units specified in a list, always show a non-

unity factor before a unit that begins with a fraction with a unity denominator.

By default, if the unit in a list begins with fraction of the form 1|

__x__and its

multiplier is an integer other than 1, the fraction is given as the product of the

multiplier and the numerator (e.g., '3|8 in' rather than '3 * 1|8 in'). In some

cases, this is not what is wanted; for example, the results for a cooking recipe

might show '3 * 1|2 cup' as '3|2 cup'. With the '--show-factor' option, a result

equivalent to 1.5 cups will display as '3 * 1|2 cup' rather than '3|2 cup'. A

user-specified fractional unit with a numerator other than 1 is never overridden,

however—if a unit list specifies '3|4 cup;1|2 cup', a result equivalent to 1 1/2

cups will always be shown as '2 * 3|4 cup' whether or not the '--show-factor'

option is given.

**-s**,

**--strict**

Suppress conversion of units to their reciprocal units. For example, 'units' will

normally convert hertz to seconds because these units are reciprocals of each

other. The strict option requires that units be strictly conformable to perform a

conversion, and will give an error if you attempt to convert hertz to seconds.

**-1**,

**--one-line**

Give only one line of output (the forward conversion). Do not print the reverse

conversion. If a reciprocal conversion is performed then 'units' will still print

the ``reciprocal conversion'' line.

**-t**,

**--terse**

Give terse output when converting units. This option can be used when calling

'units' from another program so that the output is easy to parse. This option has

the combined effect of these options: '--strict' '--quiet' '--one-line'

'--compact'. When combined with '--version' it produces a display showing only the

program name and version number.

**-v**,

**--verbose**

Give slightly more verbose output when converting units. When combined with the

'-c' option this gives the same effect as '--check-verbose'. When combined with

'--version' produces a more detailed output, equivalent to the '--info' option.

**-V**,

**--version**

Print the program version number, tell whether the 'readline' library has been

included, tell whether UTF-8 support has been included; give the locale, the

location of the default units data file, and the location of the personal units

data file; indicate if the personal units data file does not exist.

When given in combination with the '--terse' option, the program prints only the version

number and exits.

When given in combination with the '--verbose' option, the program, the '--version' option

has the same effect as the '--info' option below.

**-I**,

**--info**

Print the information given with the '--version' option, show the pathname of the

units program, show the status of the 'UNITSFILE' and 'MYUNITSFILE' environment

variables, and additional information about how 'units' locates the related files.

On systems running Microsoft Windows, the status of the 'UNITSLOCALE' environment

variable and information about the related locale map are also given. This option

is usually of interest only to developers and administrators, but it can sometimes

be useful for troubleshooting.

Combining the '--version' and '--verbose' options has the same effect as giving '--info'.

**-U**,

**--unitsfile**

Print the location of the default units data file and exit; if the file cannot be

found, print ``Units data file not found''.

**-l**

__locale__,

**--locale**

__locale__

Print the information given with the '--version' option, show the Force a specified

locale such as 'en_GB' to get British definitions by default. This overrides the

locale determined from system settings or environment variables. See

__Locale__for a

description of locale format.

**ADDING** **YOUR** **OWN** **DEFINITIONS**

**Units**

**Data**

**Files**

The units and prefixes that 'units' can convert are defined in the units data file,

typically '/usr/share/units/definitions.units'. If you can't find this file, run

'units --version' to get information on the file locations for your installation.

Although you can extend or modify this data file if you have appropriate user privileges,

it's usually better to put extensions in separate files so that the definitions will be

preserved if you update 'units'.

You can include additional data files in the units database using the '!include' command

in the standard units data file. For example

!include /usr/local/share/units/local.units

might be appropriate for a site-wide supplemental data file. The location of the

'!include' statement in the standard units data file is important; later definitions

replace earlier ones, so any definitions in an included file will override definitions

before the '!include' statement in the standard units data file. With normal invocation,

no warning is given about redefinitions; to ensure that you don't have an unintended

redefinition, run 'units -c' after making changes to any units data file.

If you want to add your own units in addition to or in place of standard or site-wide

supplemental units data files, you can include them in the '.units' file in your home

directory. If this file exists it is read after the standard units data file, so that any

definitions in this file will replace definitions of the same units in the standard data

file or in files included from the standard data file. This file will not be read if any

units files are specified on the command line. (Under Windows the personal units file is

named 'unitdef.units'.) Running 'units -V' will display the location and name of your

personal units file.

The 'units' program first tries to determine your home directory from the 'HOME'

environment variable. On systems running Microsoft Windows, if 'HOME' does not exist,

'units' attempts to find your home directory from 'HOMEDRIVE', 'HOMEPATH' and

'USERPROFILE'. You can specify an arbitrary file as your personal units data file with

the 'MYUNITSFILE' environment variable; if this variable exists, its value is used without

searching your home directory. The default units data files are described in more detail

in

__Data__

__Files__.

**Defining**

**New**

**Units**

**and**

**Prefixes**

A unit is specified on a single line by giving its name and an equivalence. Comments

start with a '#' character, which can appear anywhere in a line. The backslash character

('\') acts as a continuation character if it appears as the last character on a line,

making it possible to spread definitions out over several lines if desired. A file can be

included by giving the command '!include' followed by the file's name. The '!' must be

the first character on the line. The file will be sought in the same directory as the

parent file unless you give a full path. The name of the file to be included cannot

contain the comment character '#'.

Unit names must not contain any of the operator characters '+', '-', '*', '/', '|', '^',

';', '~', the comment character '#', or parentheses. They cannot begin or end with an

underscore ('_'), a comma (',') or a decimal point ('.'). The figure dash (U+2012),

typographical minus (`-'; U+2212), and en dash (`-'; U+2013) are converted to the operator

'-', so none of these characters can appear in unit names. Names cannot begin with a

digit, and if a name ends in a digit other than zero, the digit must be preceded by a

string beginning with an underscore, and afterwards consisting only of digits, decimal

points, or commas. For example, 'foo_2', 'foo_2,1', or 'foo_3.14' are valid names but

'foo2' or 'foo_a2' are invalid. You could define nitrous oxide as

N2O nitrogen 2 + oxygen

but would need to define nitrogen dioxide as

NO_2 nitrogen + oxygen 2

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. Dimensionless units are indicated

by using the string '!dimensionless' for the unit definition.

When adding new units, be sure to use the '-c' option to check that the new units reduce

properly. If you create a loop in the units definitions, then 'units' will hang when

invoked with the '-c' option. You will need to use the '--check-verbose' option, which

prints out each unit as it is checked. The program will still hang, but the last unit

printed will be the unit that caused the infinite loop.

If you define any units that contain '+' characters, carefully check them because the '-c'

option will not catch non-conformable sums. Be careful with the '-' operator as well.

When used as a binary operator, the '-' character can perform addition or multiplication

depending on the options used to invoke 'units'. To ensure consistent behavior use '-'

only as a unary negation operator when writing units definitions. To multiply two units

leave a space or use the '*' operator with care, recalling that it has two possible

precedence values and may require parentheses to ensure consistent behavior. To compute

the difference of 'foo' and 'bar' write 'foo+(-bar)' or even 'foo+-bar'.

Here is an example of a short data file that defines some basic units:

m ! # The meter is a primitive unit

sec ! # The second is a primitive unit

rad !dimensionless # A dimensionless primitive unit

micro- 1e-6 # Define a prefix

minute 60 sec # A minute is 60 seconds

hour 60 min # An hour is 60 minutes

inch 0.0254 m # Inch defined in terms of meters

ft 12 inches # The foot defined in terms of inches

mile 5280 ft # And the mile

A unit that ends with a '-' character is a prefix. If a prefix definition contains any

'/' characters, be sure they are protected by parentheses. If you define 'half- 1/2' then

'halfmeter' would be equivalent to '1 / (2 meter)'.

**Defining**

**Nonlinear**

**Units**

Some unit conversions of interest are nonlinear; for example, temperature conversions

between the Fahrenheit and Celsius scales cannot be done by simply multiplying by

conversion factors.

When you give a linear unit definition such as 'inch 2.54 cm' you are providing

information that 'units' uses to convert values in inches into primitive units of meters.

For nonlinear units, you give a functional definition that provides the same information.

Nonlinear units are represented using a functional notation. It is best to regard this

notation not as a function call but as a way of adding units to a number, much the same

way that writing a linear unit name after a number adds units to that number. Internally,

nonlinear units are defined by a pair of functions that convert to and from linear units

in the database, so that an eventual conversion to primitive units is possible.

Here is an example nonlinear unit definition:

tempF(x) units=[1;K] domain=[-459.67,) range=[0,) \

(x+(-32)) degF + stdtemp ; (tempF+(-stdtemp))/degF + 32

A nonlinear unit definition comprises a unit name, a formal parameter name, two functions,

and optional specifications for units, the domain, and the range (the domain of the

inverse function). The functions tell 'units' how to convert to and from the new unit.

To produce valid results, the arguments of these functions need to have the correct

dimensions and be within the domains for which the functions are defined.

The definition begins with the unit name followed immediately (with no spaces) by a '('

character. In the parentheses is the name of the formal parameter. Next is an optional

specification of the units required by the functions in the definition. In the example

above, the 'units=[1;K]' specification indicates that the 'tempF' function requires an

input argument conformable with '1' (i.e., the argument is dimensionless), and that the

inverse function requires an input argument conformable with 'K'. For normal nonlinear

units definition, the forward function will always take a dimensionless argument; in

general, the inverse function will need units that match the quantity measured by your

nonlinear unit. Specifying the units enables 'units' to perform error checking on

function arguments, and also to assign units to domain and range specifications, which are

described later.

Next the function definitions appear. In the example above, the 'tempF' function is

defined by

tempF(x) = (x+(-32)) degF + stdtemp

This gives a rule for converting 'x' in the units 'tempF' to linear units of absolute

temperature, which makes it possible to convert from tempF to other units.

To enable conversions to Fahrenheit, you must give a rule for the inverse conversions.

The inverse will be 'x(tempF)' and its definition appears after a ';' character. In our

example, the inverse is

x(tempF) = (tempF+(-stdtemp))/degF + 32

This inverse definition takes an absolute temperature as its argument and converts it to

the Fahrenheit temperature. The inverse can be omitted by leaving out the ';' character

and the inverse definition, but then conversions

__to__the unit will not be possible. If the

inverse definition is omitted, the '--check' option will display a warning. It is up to

you to calculate and enter the correct inverse function to obtain proper conversions; the

'--check' option tests the inverse at one point and prints an error if it is not valid

there, but this is not a guarantee that your inverse is correct.

With some definitions, the units may vary. For example, the definition

square(x) x^2

can have any arbitrary units, and can also take dimensionless arguments. In such a case,

you should

__not__specify units. If a definition takes a root of its arguments, the

definition is valid only for units that yield such a root. For example,

squirt(x) sqrt(x)

is valid for a dimensionless argument, and for arguments with even powers of units.

Some definitions may not be valid for all real numbers. In such cases, 'units' can handle

errors better if you specify an appropriate domain and range. You specify the domain and

range as shown below:

baume(d) units=[1;g/cm^3] domain=[0,130.5] range=[1,10] \

(145/(145-d)) g/cm^3 ; (baume+-g/cm^3) 145 / baume

In this example the domain is specified after 'domain=' with the endpoints given in

brackets. In accord with mathematical convention, square brackets indicate a closed

interval (one that includes its endpoints), and parentheses indicate an open interval (one

that does not include its endpoints). An interval can be open or closed on one or both

ends; an interval that is unbounded on either end is indicated by omitting the limit on

that end. For example, a quantity to which decibel (dB) is applied may have any value

greater than zero, so the range is indicated by '(0,)':

decibel(x) units=[1;1] range=(0,) 10^(x/10); 10 log(decibel)

If the domain or range is given, the second endpoint must be greater than the first.

The domain and range specifications can appear independently and in any order along with

the units specification. The values for the domain and range endpoints are attached to

the units given in the units specification, and if necessary, the parameter value is

adjusted for comparison with the endpoints. For example, if a definition includes

'units=[1;ft]' and 'range=[3,)', the range will be taken as 3 ft to infinity. If the

function is passed a parameter of '900 mm', that value will be adjusted to 2.9527559 ft,

which is outside the specified range. If you omit the units specification from the

previous example, 'units' can not tell whether you intend the lower endpoint to be 3 ft or

3 microfurlongs, and can not adjust the parameter value of 900 mm for comparison. Without

units, numerical values other than zero or plus or minus infinity for domain or range

endpoints are meaningless, and accordingly they are not allowed. If you give other values

without units then the definition will be ignored and you will get an error message.

Although the units, domain, and range specifications are optional, it's best to give them

when they are applicable; doing so allows 'units' to perform better error checking and

give more helpful error messages. Giving the domain and range also enables the '--check'

option to find a point in the domain to use for its point check of your inverse

definition.

You can make synonyms for nonlinear units by providing both the forward and inverse

functions; inverse functions can be obtained using the '~' operator. So to create a

synonym for 'tempF' you could write

fahrenheit(x) units=[1;K] tempF(x); ~tempF(fahrenheit)

This is useful for creating a nonlinear unit definition that differs slightly from an

existing definition without having to repeat the original functions. For example,

dBW(x) units=[1;W] range=[0,) dB(x) W ; ~dB(dBW/W)

If you wish a synonym to refer to an existing nonlinear unit without modification, you can

do so more simply by adding the synonym with appended parentheses as a new unit, with the

existing nonlinear unit—without parentheses—as the definition. So to create a synonym for

'tempF' you could write

fahrenheit() tempF

The definition must be a nonlinear unit; for example, the synonym

fahrenheit() meter

will result in an error message when 'units' starts.

You may occasionally wish to define a function that operates on units. This can be done

using a nonlinear unit definition. For example, the definition below provides conversion

between radius and the area of a circle. This definition requires a length as input and

produces an area as output, as indicated by the 'units=' specification. Specifying the

range as the nonnegative numbers can prevent cryptic error messages.

circlearea(r) units=[m;m^2] range=[0,) pi r^2 ; sqrt(circlearea/pi)

**Defining**

**Piecewise**

**Linear**

**Units**

Sometimes you may be interested in a piecewise linear unit such as many wire gauges.

Piecewise linear units can be defined by specifying conversions to linear units on a list

of points. Conversion at other points will be done by linear interpolation. A partial

definition of zinc gauge is

zincgauge[in] 1 0.002, 10 0.02, 15 0.04, 19 0.06, 23 0.1

In this example, 'zincgauge' is the name of the piecewise linear unit. The definition of

such a unit is indicated by the embedded '[' character. After the bracket, you should

indicate the units to be attached to the numbers in the table. No spaces can appear

before the ']' character, so a definition like 'foo[kg meters]' is invalid; instead write

'foo[kg*meters]'. The definition of the unit consists of a list of pairs optionally

separated by commas. This list defines a function for converting from the piecewise

linear unit to linear units. The first item in each pair is the function argument; the

second item is the value of the function at that argument (in the units specified in

brackets). In this example, we define 'zincgauge' at five points. For example, we set

'zincgauge(1)' equal to '0.002 in'. Definitions like this may be more readable if

written using continuation characters as

zincgauge[in] \

1 0.002 \

10 0.02 \

15 0.04 \

19 0.06 \

23 0.1

With the preceding definition, the following conversion can be performed:

You have: zincgauge(10)

You want: in

* 0.02

/ 50

You have: .01 inch

You want: zincgauge

5

If you define a piecewise linear unit that is not strictly monotonic, then the inverse

will not be well defined. If the inverse is requested for such a unit, 'units' will

return the smallest inverse.

After adding nonlinear units definitions, you should normally run 'units --check' to check

for errors. If the 'units' keyword is not given, the '--check' option checks a nonlinear

unit definition using a dimensionless argument, and then checks using an arbitrary

combination of units, as well as the square and cube of that combination; a warning is

given if any of these tests fail. For example,

Warning: function 'squirt(x)' defined as 'sqrt(x)'

failed for some test inputs:

squirt(7(kg K)^1): Unit not a root

squirt(7(kg K)^3): Unit not a root

Running 'units --check' will print a warning if a non-monotonic piecewise linear unit is

encountered. For example, the relationship between ANSI coated abrasive designation and

mean particle size is non-monotonic in the vicinity of 800 grit:

ansicoated[micron] \

. . .

600 10.55 \

800 11.5 \

1000 9.5 \

Running 'units --check' would give the error message

Table 'ansicoated' lacks unique inverse around entry 800

Although the inverse is not well defined in this region, it's not really an error.

Viewing such error messages can be tedious, and if there are enough of them, they can

distract from true errors. Error checking for nonlinear unit definitions can be

suppressed by giving the 'noerror' keyword; for the examples above, this could be done as

squirt(x) noerror domain=[0,) range=[0,) sqrt(x); squirt^2

ansicoated[micron] noerror \

. . .

Use the 'noerror' keyword with caution. The safest approach after adding a nonlinear unit

definition is to run 'units --check' and confirm that there are no actual errors before

adding the 'noerror' keyword.

**Defining**

**Unit**

**List**

**Aliases**

Unit list aliases are treated differently from unit definitions, because they are a data

entry shorthand rather than a true definition for a new unit. A unit list alias

definition begins with '!unitlist' and includes the alias and the definition; for

example, the aliases included in the standard units data file are

!unitlist hms hr;min;sec

!unitlist time year;day;hr;min;sec

!unitlist dms deg;arcmin;arcsec

!unitlist ftin ft;in;1|8 in

!unitlist usvol cup;3|4 cup;2|3 cup;1|2 cup;1|3 cup;1|4 cup;\

tbsp;tsp;1|2 tsp;1|4 tsp;1|8 tsp

Unit list aliases are only for unit lists, so the definition must include a ';'. Unit

list aliases can never be combined with units or other unit list aliases, so the

definition of 'time' shown above could

__not__have been shortened to 'year;day;hms'.

As usual, be sure to run 'units --check' to ensure that the units listed in unit list

aliases are conformable.

**NUMERIC** **OUTPUT** **FORMAT**

By default, 'units' shows results to eight significant digits. You can change this with

the '--exponential', '--digits', and '--output-format' options. The first sets an

exponential format (i.e., scientific notation) like that used in the original Unix 'units'

program, the second allows you to specify a different number of significant digits, and

the last allows you to control the output appearance using the format for the 'printf()'

function in the C programming language. If you only want to change the number of

significant digits or specify exponential format type, use the '--digits' and

'--exponential' options. The '--output-format' option affords the greatest control of the

output appearance, but requires at least rudimentary knowledge of the 'printf()' format

syntax. See

__Invoking__

__Units__for descriptions of these options.

**Format**

**Specification**

The format specification recognized with the '--output-format' option is a subset of that

for 'printf()'. The format specification has the form

'%'[

__flags__][

__width__]['.'

__precision__]

__type__; it must begin with '%', and must end with a floating-

point type specifier: 'g' or 'G' to specify the number of significant digits, 'e' or 'E'

for scientific notation, and 'f' for fixed-point decimal. The ISO C99 standard added the

'F' type for fixed-point decimal and the 'a' and 'A' types for hexadecimal floating point;

these types are allowed with compilers that support them. Type length modifiers (e.g.,

'L' to indicate a long double) are inapplicable and are not allowed.

The default format for 'units' is '%.8g'; for greater precision, you could specify

'-o %.15g'. The 'g' and 'G' format types use exponential format whenever the exponent

would be less than -4, so the value 0.000013 displays as '1.3e-005'. These types also use

exponential notation when the exponent is greater than or equal to the precision, so with

the default format, the value 5e7 displays as '50000000' and the value 5e8 displays as

'5e+008'. If you prefer fixed-point display, you might specify '-o %.8f'; however, small

numbers will display very few significant digits, and values less than 0.5e-8 will show

nothing but zeros.

The format specification may include one or more optional flags: '+', ' ' (space), '#',

'-', or '0' (the digit zero). The digit-grouping flag ''' is allowed with compilers that

support it. Flags are followed by an optional value for the minimum field width, and an

optional precision specification that begins with a period (e.g., '.6'). The field width

includes the digits, decimal point, the exponent, thousands separators (with the digit-

grouping flag), and the sign if any of these are shown.

**Flags**

The '+' flag causes the output to have a sign ('+' or '-'). The space flag ' ' is similar

to the '+' flag, except that when the value is positive, it is prefixed with a space

rather than a plus sign; this flag is ignored if the '+' flag is also given. The '+' or

' ' flag could be useful if conversions might include positive and negative results, and

you wanted to align the decimal points in exponential notation. The '#' flag causes the

output value to contain a decimal point in all cases; by default, the output contains a

decimal point only if there are digits (which can be trailing zeros) to the right of the

point. With the 'g' or 'G' types, the '#' flag also prevents the suppression of trailing

zeros. The digit-grouping flag ''' shows a thousands separator in digits to the left of

the decimal point. This can be useful when displaying large numbers in fixed-point

decimal; for example, with the format '%f',

You have: mile

You want: microfurlong

* 8000000.000000

/ 0.000000

the magnitude of the first result may not be immediately obvious without counting the

digits to the left of the decimal point. If the thousands separator is the comma (','),

the output with the format '%'f' might be

You have: mile

You want: microfurlong

* 8,000,000.000000

/ 0.000000

making the magnitude readily apparent. Unfortunately, few compilers support the digit-

grouping flag.

With the '-' flag, the output value is left aligned within the specified field width. If

a field width greater than needed to show the output value is specified, the '0' (zero)

flag causes the output value to be left padded with zeros until the specified field width

is reached; for example, with the format '%011.6f',

You have: troypound

You want: grain

* 5760.000000

/ 0000.000174

The '0' flag has no effect if the '-' (left align) flag is given.

**Field**

**Width**

By default, the output value is left aligned and shown with the minimum width necessary

for the specified (or default) precision. If a field width greater than this is

specified, the value shown is right aligned, and padded on the left with enough spaces to

provide the specified field width. A width specification is typically used with fixed-

point decimal to have columns of numbers align at the decimal point; this arguably is less

useful with 'units' than with long columnar output, but it may nonetheless assist in

quickly assessing the relative magnitudes of results. For example, with the format

'%12.6f',

You have: km

You want: in

* 39370.078740

/ 0.000025

You have: km

You want: rod

* 198.838782

/ 0.005029

You have: km

You want: furlong

* 4.970970

/ 0.201168

**Precision**

The meaning of ``precision'' depends on the format type. With 'g' or 'G', it specifies

the number of significant digits (like the '--digits' option); with 'e', 'E', 'f', or 'F',

it specifies the maximum number of digits to be shown after the decimal point.

With the 'g' and 'G' format types, trailing zeros are suppressed, so the results may

sometimes have fewer digits than the specified precision (as indicated above, the '#' flag

causes trailing zeros to be displayed).

The default precision is 6, so '%g' is equivalent to '%.6g', and would show the output to

six significant digits. Similarly, '%e' or '%f' would show the output with six digits

after the decimal point.

The C 'printf()' function allows a precision of arbitrary size, whether or not all of the

digits are meaningful. With most compilers, the maximum internal precision with 'units'

is 15 decimal digits (or 13 hexadecimal digits). With the '--digits' option, you are

limited to the maximum internal precision; with the '--output-format' option, you may

specify a precision greater than this, but it may not be meaningful. In some cases,

specifying excess precision can result in rounding artifacts. For example, a pound is

exactly 7000 grains, but with the format '%.18g', the output might be

You have: pound

You want: grain

* 6999.9999999999991

/ 0.00014285714285714287

With the format '%.25g' you might get the following:

You have: 1/3

You want:

Definition: 0.333333333333333314829616256247

In this case the displayed value includes a series of digits that represent the underlying

binary floating-point approximation to 1/3 but are not meaningful for the desired

computation. In general, the result with excess precision is system dependent. The

precision affects only the

__display__of numbers; if a result relies on physical constants

that are not known to the specified precision, the number of physically meaningful digits

may be less than the number of digits shown.

See the documentation for 'printf()' for more detailed descriptions of the format

specification.

The '--output-format' option is incompatible with the '--exponential' or '--digits'

options; if the former is given in combination with either of the latter, the format is

controlled by the last option given.

**LOCALIZATION**

Some units have different values in different locations. The localization feature

accommodates this by allowing a units data file to specify definitions that depend on the

user's locale.

**Locale**

A locale is a subset of a user's environment that indicates the user's language and

country, and some attendant preferences, such as the formatting of dates. The 'units'

program attempts to determine the locale from the POSIX setlocale function; if this cannot

be done, 'units' examines the environment variables 'LC_CTYPE' and 'LANG'. On POSIX

systems, a locale is of the form

__language__'_'

__country__, where

__language__is the two-character

code from ISO 639-1 and

__country__is the two-character code from ISO 3166-1;

__language__is

lower case and

__country__is upper case. For example, the POSIX locale for the United Kingdom

is 'en_GB'.

On systems running Microsoft Windows, the value returned by setlocale() is different from

that on POSIX systems; 'units' attempts to map the Windows value to a POSIX value by means

of a table in the file 'locale_map.txt' in the same directory as the other data files.

The file includes entries for many combinations of language and country, and can be

extended to include other combinations. The 'locale_map.txt' file comprises two tab-

separated columns; each entry is of the form

__Windows-locale__

__POSIX-locale__

where

__POSIX-locale__is as described above, and

__Windows-locale__typically spells out both the

language and country. For example, the entry for the United States is

English_United States en_US

You can force 'units' to run in a desired locale by using the '-l' option.

In order to create unit definitions for a particular locale you begin a block of

definitions in a unit datafile with '!locale' followed by a locale name. The '!' must be

the first character on the line. The 'units' program reads the following definitions only

if the current locale matches. You end the block of localized units with '!endlocale'.

Here is an example, which defines the British gallon.

!locale en_GB

gallon 4.54609 liter

!endlocale

**Additional**

**Localization**

Sometimes the locale isn't sufficient to determine unit preferences. There could be

regional preferences, or a company could have specific preferences. Though probably

uncommon, such differences could arise with the choice of English customary units outside

of English-speaking countries. To address this, 'units' allows specifying definitions

that depend on environment variable settings. The environment variables can be controled

based on the current locale, or the user can set them to force a particular group of

definitions.

A conditional block of definitions in a units data file begins with either '!var' or

'!varnot' following by an environment variable name and then a space separated list of

values. The leading '!' must appear in the first column of a units data file, and the

conditional block is terminated by '!endvar'. Definitions in blocks beginning with '!var'

are executed only if the environment variable is exactly equal to one of the listed

values. Definitions in blocks beginning with '!varnot' are executed only if the

environment variable does

__not__equal any of the list values.

The inch has long been a customary measure of length in many places. The word comes from

the latin

__uncia__meaning ``one twelfth,'' referring to its relationship with the foot. By

the 20th century, the inch was officially defined in English-speaking countries relative

to the yard, but until 1959, the yard differed slightly among those countries. In France

the customary inch, which was displaced in 1799 by the meter, had a different length based

on a french foot. These customary definitions could be accommodated as follows:

!var INCH_UNIT usa

yard 3600|3937 m

!endvar

!var INCH_UNIT canada

yard 0.9144 meter

!endvar

!var INCH_UNIT uk

yard 0.91439841 meter

!endvar

!var INCH_UNIT canada uk usa

foot 1|3 yard

inch 1|12 foot

!endvar

!var INCH_UNIT france

foot 144|443.296 m

inch 1|12 foot

line 1|12 inch

!endvar

!varnot INCH_UNIT usa uk france canada

!message Unknown value for INCH_UNIT

!endvar

When 'units' reads the above definitions it will check the environment variable

'INCH_UNIT' and load only the definitions for the appropriate section. If 'INCH_UNIT' is

unset or is not set to one of the four values listed then 'units' will run the last block.

In this case that block uses the '!message' command to display a warning message.

Alternatively that block could set default values.

In order to create default values that are overridden by user settings the data file can

use the '!set' command, which sets an environment variable

__only__

__if__

__it__

__is__

__not__

__already__

__set__;

these settings are only for the current 'units' invocation and do not persist. So if the

example above were preceded by '!set INCH_UNIT france' then this would make 'france' the

default value for 'INCH_UNIT'. If the user had set the variable in the environment before

invoking 'units', then 'units' would use the user's value.

To link these settings to the user's locale you combine the '!set' command with the

'!locale' command. If you wanted to combine the above example with suitable locales you

could do by

__preceding__the above definition with the following:

!locale en_US

!set INCH_UNIT usa

!endlocale

!locale en_GB

!set INCH_UNIT uk

!endlocale

!locale en_CA

!set INCH_UNIT canada

!endlocale

!locale fr_FR

!set INCH_UNIT france

!endlocale

!set INCH_UNIT france

These definitions set the overall default for 'INCH_UNIT' to 'france' and set default

values for four locales appropriately. The overall default setting comes last so that it

only applies when 'INCH_UNIT' was not set by one of the other commands or by the user.

If the variable given after '!var' or '!varnot' is undefined then 'units' prints an error

message and ignores the definitions that follow. Use '!set' to create defaults to prevent

this situation from arising. The '-c' option only checks the definitions that are active

for the current environment and locale, so when adding new definitions take care to check

that all cases give rise to a well defined set of definitions.

**ENVIRONMENT** **VARIABLES**

The 'units' program uses the following environment variables:

**HOME**Specifies the location of your home directory; it is used by 'units' to find a

personal units data file '.units'. On systems running Microsoft Windows, the file

is 'unitdef.units', and if 'HOME' does not exist, 'units' tries to determine your

home directory from the 'HOMEDRIVE' and 'HOMEPATH' environment variables; if these

variables do not exist, units finally tries 'USERPROFILE'—typically

'C:\Users\

__username__' (Windows Vista and Windows 7) or

'C:\Documents and Settings\

__username__' (Windows XP).

**LC_CTYPE,**

**LANG**

Checked to determine the locale if 'units' cannot obtain it from the operating

system. Sections of the standard units data file are specific to certain locales.

**MYUNITSFILE**

Specifies your personal units data file. If this variable exists, 'units' uses its

value rather than searching your home directory for '.units'. The personal units

file will not be loaded if any data files are given using the '-f' option.

**PAGER**Specifies the pager to use for help and for displaying the conformable units. The

help function browses the units database and calls the pager using the '+n'

__n__syntax

for specifying a line number. The default pager is 'more'; 'PAGER' can be used to

specify alternatives such as 'less', 'pg', 'emacs', or 'vi'.

**UNITS_ENGLISH**

Set to either 'US' or 'GB' to choose United States or British volume definitions,

overriding the default from your locale.

**UNITSFILE**

Specifies the units data file to use (instead of the default). You can only

specify a single units data file using this environment variable. If units data

files are given using the '-f' option, the file specified by 'UNITSFILE' will be

not be loaded unless the '-f' option is given with the empty string

('units -f ""').

**UNITSLOCALEMAP**

Windows only; this variable has no effect on Unix-like systems. Specifies the

units locale map file to use (instead of the default). This variable seldom needs

to be set, but you can use it to ensure that the locale map file will be found if

you specify a location for the units data file using either the '-f' option or the

'UNITSFILE' environment variable, and that location does not also contain the

locale map file.

**DATA** **FILES**

The 'units' program uses two default data files: 'definitions.units' and 'currency.units'.

The program can also use an optional personal units data file '.units' ('unitdef.units'

under Windows) located in the user's home directory. The personal units data file is

described in more detail in

__Units__

__Data__

__Files__.

On Unix-like systems, the data files are typically located in '/usr/share/units' if

'units' is provided with the operating system, or in '/usr/local/share/units' if 'units'

is compiled from the source distribution.

On systems running Microsoft Windows, the files may be in the same locations if Unix-like

commands are available, a Unix-like file structure is present (e.g., 'C:/usr/local'), and

'units' is compiled from the source distribution. If Unix-like commands are not

available, a more common location is 'C:\Program Files (x86)\GNU\units' (for 64-bit

Windows installations) or 'C:\Program Files\GNU\units' (for 32-bit installations).

If 'units' is obtained from the GNU Win32 Project (http://gnuwin32.sourceforge.net/), the

files are commonly in 'C:\Program Files\GnuWin32\share\units'.

If the default units data file is not an absolute pathname, 'units' will look for the file

in the directory that contains the 'units' program; if the file is not found there,

'units' will look in a directory '../share/units' relative to the directory with the

'units' program.

You can determine the location of the files by running 'units --version'. Running

'units --info' will give you additional information about the files, how 'units' will

attempt to find them, and the status of the related environment variables.

**UNICODE** **SUPPORT**

The standard units data file is in Unicode, using UTF-8 encoding. Most definitions use

only ASCII characters (i.e., code points U+0000 through U+007F); definitions using non-

ASCII characters appear in blocks beginning with '!utf8' and ending with '!endutf8'.

When 'units' starts, it checks the locale to determine the character set. If 'units' is

compiled with Unicode support and definitions; otherwise these definitions are ignored.

When Unicode support is active, 'units' will check every line of all of the units data

files for invalid or non-printing UTF-8 sequences; if such sequences occur, 'units'

ignores the entire line. In addition to checking validity, 'units' determines the display

width of non-ASCII characters to ensure proper positioning of the pointer in some error

messages and to align columns for the 'search' and '?' commands.

At present, 'units' does not support Unicode under Microsoft Windows. The UTF-16 and

UTF-32 encodings are not supported on any systems.

If definitions that contain non-ASCII characters are added to a units data file, those

definitions should be enclosed within '!utf8' ... '!endutf8' to ensure that they are only

loaded when Unicode support is available. As usual, the '!' must appear as the first

character on the line. As discussed in

__Units__

__Data__

__Files__, it's usually best to put such

definitions in supplemental data files linked by an '!include' command or in a personal

units data file.

When Unicode support is not active, 'units' makes no assumptions about character encoding,

except that characters in the range 00-7F hexadecimal correspond to ASCII encoding. Non-

ASCII characters are simply sequences of bytes, and have no special meanings; for

definitions in supplementary units data files, you can use any encoding consistent with

this assumption. For example, if you wish to use non-ASCII characters in definitions when

running 'units' under Windows, you can use a character set such as Windows ``ANSI'' (code

page 1252 in the US and Western Europe). You can even use UTF-8, though some messages may

be improperly aligned, and 'units' will not detect invalid UTF-8 sequences. If you use

UTF-8 encoding when Unicode support is not active, you should place any definitions with

non-ASCII characters

__outside__'!utf8' ... '!endutf8' blocks—otherwise, they will be

ignored.

Typeset material other than code examples usually uses the Unicode minus (U+2212) rather

than the ASCII hyphen-minus operator (U+002D) used in 'units'; the figure dash (U+2012)

and en dash (U+2013) are also occasionally used. To allow such material to be copied and

pasted for interactive use or in units data files, 'units' converts these characters to

U+002D before further processing. Because of this, none of these characters can appear in

unit names.

**READLINE** **SUPPORT**

If the 'readline' package has been compiled in, then when 'units' is used interactively,

numerous command line editing features are available. To check if your version of 'units'

includes 'readline', invoke the program with the '--version' option.

For complete information about 'readline', consult the documentation for the 'readline'

package. Without any configuration, 'units' will allow editing in the style of emacs. Of

particular use with 'units' are the completion commands.

If you type a few characters and then hit

__ESC__followed by '

__?__' then 'units' will display a

list of all the units that start with the characters typed. For example, if you type

'

__metr__' and then request completion, you will see something like this:

You have: metr

metre metriccup metrichorsepower metrictenth

metretes metricfifth metricounce metricton

metriccarat metricgrain metricquart metricyarncount

You have: metr

If there is a unique way to complete a unitname, you can hit the

__TAB__key and 'units' will

provide the rest of the unit name. If 'units' beeps, it means that there is no unique

completion. Pressing the

__TAB__key a second time will print the list of all completions.

The readline library also keeps a history of the values you enter. You can move through

this history using the up and down arrows. The history is saved to the file

'.units_history' in your home directory so that it will persist across multiple 'units'

invocations. If you wish to keep work for a certain project separate you can change the

history filename using the '--history' option. You could, for example, make an alias for

'units' to 'units --history .units_history' so that 'units' would save separate history in

the current directory. The length of each history file is limited to 5000 lines. Note

also that if you run several concurrent copies of 'units' each one will save its new

history to the history file upon exit.

**UPDATING** **CURRENCY** **EXCHANGE** **RATES**

The units program includes currency exchange rates and prices for some precious metals in

the database. Of course, these values change over time, sometimes very rapidly, and

'units' cannot provide real time values. To update the exchange rates run the

'units_cur', which rewrites the files containing the currency rates, typically

'/usr/share/units/currency.units'. This program requires 'python' and the 'unidecode'

package, and must be run with suitable permissions to write the file. To keep the rates

updated automatically, run it using a cron job on a Unix-like system, or a similar

scheduling program on a different system. Currency exchange rates are taken from Time

Genie (http://www.timegenie.com) and precious metals pricing from Packetizer

(www.packetizer.com). These sites update once per day, so there is no benefit in running

the update script more often than daily. You can run 'units_cur' with a filename

specified on the command line and it will write the data to that file. If you give '-'

for the file it will write to standard output.

**DATABASE** **COMMAND** **SYNTAX**

__unit__

__definition__

Define a regular unit.

__prefix__

**-**

__definition__

Define a prefix.

__funcname__

**(**

__var__

**)**

**noerror**

**units=[**

__in-units__

**,**

__out-units__

**]**

**domain=[**

__x1__

**,**

__x2__

**]**

**range=[**

__y1__

**,**

__y2__

**]**

__definition(var)__

**;**

__inverse(funcname)__

Define a nonlinear unit or unit function. The four optional keywords 'noerror',

'units=', 'range=' and 'domain=' can appear in any order. The definition of the

inverse is optional.

__tabname__

**[**

__out-units__

**]**

**noerror**

__pair-list__

Define a piecewise linear unit. The pair list gives the points on the table listed

in ascending order. The 'noerror' keyword is optional.

**!endlocale**

End a block of definitions beginning with '!locale'

**!endutf8**

End a block of definitions begun with '!utf8'

**!endvar**

End a block of definitions begun with '!var' or '!varnot'

**!include**

__file__

Include the specified file.

**!locale**

__value__

Load the following definitions only of the locale is set to

__value__.

**!message**

__text__

Display

__text__when the database is read unless the quiet option ('-q') is enabled.

**!set**

__variable__

__value__

Sets the environment variable,

__variable__, to the specified value

__only__

__if__it is not

already set.

**!unitlist**

__alias__

__definition__

Define a unit list alias.

**!utf8**Load the following definitions only if 'units' is running with UTF-8 enabled.

**!var**

__envar__

__value-list__

Load the block of definitions that follows only if the environment variable

__envar__

is set to one of the values listed in the space-separated value list. If

__envar__is

not set, 'units' prints an error message and ignores the block of definitions.

**!varnot**

__envar__

__value-list__

Load the block of definitions that follows only if the environment variable

__envar__

is set to value that is

__not__listed in the space-separated value list. If

__envar__is

not set, 'units' prints an error message and ignores the block of definitions.

**GNU** **FREE** **DOCUMENTATION** **LICENSE**

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