# FreeBSD Manual Pages

UNITS(1) General Commands Manual UNITS(1)NAMEunits -- unit conversion and calculation programSYNOPSIS'units' [options] [from-unit[to-unit]]DESCRIPTIONThe '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; seeTemperatureConversions. 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 convertfromand the units that you want to convertto. You can use the pro- gram interactively with prompts, or you can use it from the command line. Beyond simple unit conversions, 'units' can be used as a general-pur- pose scientific calculator that keeps track of units in its calcula- tions. 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 consis- tency when working with long expressions that involve many different units that may combine in complex ways; for an illustration, seeCom-plicatedUnitExpressions. The units are defined in an external data file. You can use the exten- sive 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. SeeInvokingUnitsfor a description of the available options.INTERACTINGWITHUNITSTo 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 convertingfrom. For example, if you want to convert ten meters to feet, type '10meters'. Next, 'units' will print 'You want:'. You should type the units you want to convertto. To convert to feet, you would type 'feet'. If the 'readline' library was compiled in thentabwill complete unit names. SeeReadlineSupportfor more information about 'readline'. To quit the program under Unix, pressCtrl-CorCtrl-D. Under Windows, pressCtrl-CorCtrl-Z; with the latter, you may also need to pressEnter. 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 num- ber 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 obvi- ous 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 dis- play 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, sim- ply pressEnterat 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 combina- tion 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 con- formable with the unit that you entered at the 'You have:' prompt above. Conformable unitcombinationswill 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 histori- cal information about the unit. (You can generally quit out of the page by pressing 'q'.) Typing 'search'textwill display a list of all of the units whose names containtextas a substring along with their definitions. This may help in the case where you aren't sure of the right unit name.USINGThe '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 expres- sion contains non-alphanumeric characters, you may need to protect it from interpretation by the shell using single or double quote charac- ters. 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.UNITSNON-INTERACTIVELYUNIT DEFINITIONSThe 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 common spelled-out numbers (e.g., 'seventeen') are recognized. 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 vari- ous 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.EnglishCustomaryUnitsEnglish 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 Impe- rial 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 val- ues 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 theInterna-tionalYard. 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 theUSsurveyfoot. The US defined aUSsurveymileas 5280 US survey feet, and defined astatutemileas a US survey mile. The US values for these units differ from the international val- ues 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' pre- fix. 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' (butnot'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 EXPRESSIONSOperatorsYou 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. Addition- ally, 'units' supports some extensions, including high priority multi- plication using a space, and a high priority numerical division opera- tor ('|') that can simplify some expressions. You multiply units using a space or an asterisk ('*'). The next exam- ple 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 White space surrounding operators is optional, so the previous example could have used '(1/2)kg/(kg/meter)'. As a consequence, however, hyphenated spelled-out numbers (e.g., 'forty-two') cannot be used; 'forty-two' is interpreted as '40 - 2'. 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 advanta- geous. 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 ofnumberswith 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 prod- ucts 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 sec- ond 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 meaning- ful (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 numberp/q, and the dimension of the unit must be a power ofq, 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 parenthe- ses 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 haveq< 100. When raising a non-dimensionless unit to a power, 'units' attempts to convert a deci- mal exponent to a rational number withq< 100. If this is not possi- ble '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.SumsandDifferencesofUnitsYou may sometimes want to add values of different units that are out- side 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 mes- sage: 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 asmultiplicationso 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.NumbersasUnitsFor '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 conver- sion can precede the five. Be careful: 'units' will interpret '$5' with no space as equivalent to 'dollar^5'.Built-inFunctionsSeveral 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 rootPreviousResultYou can insert the result of the previous conversion using the under- score ('_'). 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 theradiusof the circle (seeOtherNonlinearUnits, for a more detailed description) in SI units; you want thediameterininches: 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 sym- bol, 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-interac- tively. If 'units' is invoked with the '--verbose' option (seeInvokingUnits), 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.ComplicatedUnitExpressionsThe '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 DeltaP= (8 / pi)^2 (rhofLQ^2) /d^5, where DeltaPis the pressure drop, rho is the mass density,fis the (dimensionless) friction factor,Lis the length of the pipe,Qis the volumetric flow rate, anddis the pipe diameter. It might be desired to have the equation in the form DeltaP= A1 rhofLQ^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 / 0.022970568BackwardsCompatibility:'*' 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 prece- dence, and can be confusing for people who think of units as a calcula- tor. 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 oper- ator 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. Regard- less 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 CONVERSIONSNonlinear units are represented using functional notation. They make possible nonlinear unit conversions such as temperature.TemperatureConversionsConversions between temperatures are different from linear conversions between temperatureincrements--see the example below. The absolute temperature conversions are handled by units starting with 'temp', and you must use functional notation. The temperature-increment conver- sions 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 thatxshould have units of 'tempF' attached to it. SeeDefiningNon-linearUnits. 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 'tempX' units when convert- ing to a temperature rather than converting a temperature increment. The 'tempC()' and 'tempF()' definitions are limited to positive abso- lute 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 ^OtherNonlinearUnitsSome 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 cir- cle 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 cir- cleinch. The next example shows two ways to compute the area of a cir- cle 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 paren- theses, and pressEnterat the 'You want:' prompt to get the definition of a nonlinear unit; if the definition is not valid for all real num- bers, 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 val- ues. Nonlinear unit conversions are described in more detail inDefin-ingNonlinearUnits.UNIT LISTS: CONVERSION TO SUMS OF UNITSOutside 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 conver- sionfromsums of units was described inSumsandDifferencesofUnits, 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 convertto, 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 typi- cally 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 (';') char- acter: 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 coeffi- cient for the last unit. If you instead prefer to round the last coef- ficient 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 ';'doeshave 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 conform- able 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 disagree- ment 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|xand 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 cal- culations, 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, orunitlistaliases, 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, zerosareincluded in this output list: You have: liter You want: cup;1|2 cup;1|4 cup;tbsp 4;0;0;3.6280454LOGGING CALCULATIONSThe '--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 inComplicatedUnitExpressions, 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, includ- ing 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.INVOKINGUNITSYou invoke 'units' like this: units [options] [from-unit[to-unit]] If thefrom-unitandto-unitare omitted, the program will use interac- tive prompts to determine which conversions to perform. SeeInterac-tiveUse. If bothfrom-unitandto-unitare given, 'units' will print the result of that single conversion and then exit. If onlyfrom-unitappears 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. SeeCommandLineUse. 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 con- trolled 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,--checkCheck that all units and prefixes defined in the units data file reduce to primitive units. Print a list of all units that can- not be reduced. Also display some other diagnostics about sus- picious 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-checkLike 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 defi- nition. Only definitions active in the current locale are checked.-dndigits,--digitsndigitsSet 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 expo- nential 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 mean- ingful digits is 15; if you specify a greater number than your system's maximum, 'units' will print a warning and set the num- ber to the largest meaningful value. To directly set the maxi- mum value, give an argument of 'max' (e.g., '-d max'). Be aware, of course, that ``significant'' here refers only to thedisplayof 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,--exponentialSet 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.-oformat,--output-formatformatThis option affords complete control over the numeric output format using the specifiedformat. The format is a single float- ing 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 sci- entific 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 for- mat is '%.8g'; for greater precision, you could specify '-o %.15g'. SeeNumericOutputFormatand the documentation for 'printf()' for more detailed descriptions of the format specifi- cation. The '--output-format' option affords the greatest con- trol 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 pre- cision more simply with the '--digits' option or select exponen- tial format with '--exponential'. The '--output-format' option is incompatible with the '--exponential' and '--digits' options.-ffilename,--filefilenameInstruct 'units' to load the units filefilename. You can spec- ify up to 25 units files on the command line. When you use this option, 'units' will loadonlythe files you list on the command line; it will not load the standard file or your personal units file unless you explicitly list them. Iffilenameis the empty string ('-f ""'), the default units file (or that specified by 'UNITSFILE') will be loaded in addition to any others specified with '-f'.-Llogfile,--loglogfileSave the results of calculations in the filelogfile; this can be useful if it is important to have a record of unit conver- sions or other calculations that are to be used extensively or in a critical activity such as a program or design project. Iflogfileexits, the new results are appended to the file. This option is ignored when 'units' is used non-interactively. SeeLoggingCalculationsfor a more detailed description and some examples.-Hfilename,--historyfilenameInstruct 'units' to save history tofilename, so that a record of your commands is available for retrieval across different 'units' invocations. To prevent the history from being saved setfilenameto the empty string ('-H ""'). This option has no effect if readline is not available.-h,--helpPrint out a summary of the options for 'units'.-m,--minusCauses '-' to be interpreted as a subtraction operator. This is the default behavior.-p,--productCauses '-' 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.--oldstarCauses '*' to have the old-style precedence, higher than the precedence of division so that '1/2*3' will equal '1/6'.--newstarForces '*' 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'.--compactGive compact output featuring only the conversion factor. This turns off the '--verbose' option.-q,--quiet,--silentSuppress prompting of the user for units and the display of sta- tistics about the number of units loaded.-n,--nolistsDisable conversion to unit lists.-r,--roundWhen 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-factorWhen 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|xand 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,--strictSuppress 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 conver- sion, and will give an error if you attempt to convert hertz to seconds.-1,--one-lineGive 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 conver- sion'' line.-t,--terseGive terse output when converting units. This option can be used when calling 'units' from another program so that the out- put 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,--verboseGive 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,--versionPrint 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,--infoPrint 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 addi- tional 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 some- times be useful for troubleshooting. Combining the '--version' and '--verbose' options has the same effect as giving '--info'.-U,--unitsfilePrint the location of the default units data file and exit; if the file cannot be found, print ``Units data file not found''.-llocale,--localelocalePrint the information given with the '--version' option, show the Force a specified locale such as 'en_GB' to get British def- initions by default. This overrides the locale determined from system settings or environment variables. SeeLocalefor a description of locale format.ADDING YOUR OWN DEFINITIONSUnitsDataFilesThe 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 defini- tions 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 loca- tion 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 stan- dard 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'.) Run- ning '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 with- out searching your home directory. The default units data files are described in more detail inDataFiles.DefiningNewUnitsandPrefixesA unit is specified on a single line by giving its name and an equiva- lence. Comments start with a '#' character, which can appear anywhere in a line. The backslash character ('\') acts as a continuation char- acter 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 parenthe- ses. 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 defini- tions, 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 defini- tion contains any '/' characters, be sure they are protected by paren- theses. If you define 'half- 1/2' then 'halfmeter' would be equivalent to '1 / (2 meter)'.DefiningNonlinearUnitsSome unit conversions of interest are nonlinear; for example, tempera- ture 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 func- tional 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 lin- ear 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 for- mal 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 argu- ment 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 per- form 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 conversionstothe 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 argu- ments. In such a case, you shouldnotspecify 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 pow- ers 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 end- points given in brackets. In accord with mathematical convention, square brackets indicate a closed interval (one that includes its end- points), 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 deci- bel (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 speci- fication, and if necessary, the parameter value is adjusted for compar- ison 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 defini- tion. 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 orig- inal 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 mes- sages. circlearea(r) units=[m;m^2] range=[0,) pi r^2 ; sqrt(circlearea/pi)DefiningPiecewiseLinearUnitsSometimes you may be interested in a piecewise linear unit such as many wire gauges. Piecewise linear units can be defined by specifying con- versions 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 '[' charac- ter. After the bracket, you should indicate the units to be attached to the numbers in the table. No spaces can appear before the ']' char- acter, 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 per- formed: 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 piece- wise linear unit is encountered. For example, the relationship between ANSI coated abrasive designation and mean particle size is non-mono- tonic 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 con- firm that there are no actual errors before adding the 'noerror' key- word.DefiningUnitListAliasesUnit 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 couldnothave 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 FORMATBy 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 nota- tion) 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. SeeInvokingUnitsfor descriptions of these options.FormatSpecificationThe 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 pre- cision specification that begins with a period (e.g., '.6'). The field width includes the digits, decimal point, the exponent, thousands sepa- rators (with the digit-grouping flag), and the sign if any of these are shown.FlagsThe '+' flag causes the output to have a sign ('+' or '-'). The space flag ' ' is similar to the '+' flag, except that when the value is pos- itive, 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 sepa- rator 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 with- out counting the digits to the left of the decimal point. If the thou- sands 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 speci- fied 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.FieldWidthBy 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 magni- tudes 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 / 0.201168PrecisionThe 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 preci- sion (as indicated above, the '#' flag causes trailing zeros to be dis- played). 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 max- imum internal precision with 'units' is 15 decimal digits (or 13 hexa- decimal 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 arti- facts. For example, a pound is exactly 7000 grains, but with the for- mat '%.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 rep- resent 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 thedisplayof 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.LOCALIZATIONSome units have different values in different locations. The localiza- tion feature accommodates this by allowing a units data file to specify definitions that depend on the user's locale.LocaleA locale is a subset of a user's environment that indicates the user's language and country, and some attendant preferences, such as the for- matting 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 formlanguage'_'country, wherelanguageis the two-character code from ISO 639-1 andcountryis the two-character code from ISO 3166-1;languageis lower case andcountryis 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 formWindows-localePOSIX-localewherePOSIX-localeis as described above, andWindows-localetypically 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 !endlocaleAdditionalLocalizationSometimes 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 doesnotequal any of the list values. The inch has long been a customary measure of length in many places. The word comes from the latinunciameaning ``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 defini- tions 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 val- ues listed then 'units' will run the last block. In this case that block uses the '!message' command to display a warning message. Alter- natively 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 variableonlyifitisnotalreadyset; 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' com- mand with the '!locale' command. If you wanted to combine the above example with suitable locales you could do byprecedingthe above defi- nition 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 fol- low. 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 VARIABLESThe 'units' program uses the following environment variables:HOMESpecifies 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 vari- ables; 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,LANGChecked 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.MYUNITSFILESpecifies 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.PAGERSpecifies the pager to use for help and for displaying the con- formable units. The help function browses the units database and calls the pager using the '+n'nsyntax 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_ENGLISHSet to either 'US' or 'GB' to choose United States or British volume definitions, overriding the default from your locale.UNITSFILESpecifies the units data file to use (instead of the default). You can only specify a single units data file using this envi- ronment 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 ""').UNITSLOCALEMAPWindows 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 spec- ify a location for the units data file using either the '-f' option or the 'UNITSFILE' environment variable, and that loca- tion does not also contain the locale map file.DATA FILESThe '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 inUnitsDataFiles. 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 dis- tribution. On systems running Microsoft Windows, the files may be in the same locations if Unix-like commands are available, a Unix-like file struc- ture 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' pro- gram; 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 SUPPORTThe 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 begin- ning 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; oth- erwise 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 inUnitsDataFiles, 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 hexadeci- mal 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 char- acters 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 charactersout-side'!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 charac- ters to U+002D before further processing. Because of this, none of these characters can appear in unit names.READLINE SUPPORTIf the 'readline' package has been compiled in, then when 'units' is used interactively, numerous command line editing features are avail- able. 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 hitESCfollowed by '?' then 'units' will display a list of all the units that start with the char- acters typed. For example, if you type 'metr' and then request comple- tion, 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 theTABkey and 'units' will provide the rest of the unit name. If 'units' beeps, it means that there is no unique completion. Pressing theTABkey 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 his- tory 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 RATESThe 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 val- ues. 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 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. Cur- rency exchange rates are taken from Yahoo (http://finance.yahoo.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 out- put.DATABASE COMMAND SYNTAXunitdefinitionDefine a regular unit.prefix-definitionDefine a prefix.funcname(var)noerrorunits=[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]noerrorpair-listDefine a piecewise linear unit. The pair list gives the points on the table listed in ascending order. The 'noerror' keyword is optional.!endlocaleEnd a block of definitions beginning with '!locale'!endutf8End a block of definitions begun with '!utf8'!endvarEnd a block of definitions begun with '!var' or '!varnot'!includefileInclude the specified file.!localevalueLoad the following definitions only of the locale is set tovalue.!messagetextDisplaytextwhen the database is read unless the quiet option ('-q') is enabled.!setvariablevalueSets the environment variable,variable, to the specified valueonlyifit is not already set.!unitlistaliasdefinitionDefine a unit list alias.!utf8Load the following definitions only if 'units' is running with UTF-8 enabled.!varenvarvalue-listLoad the block of definitions that follows only if the environ- ment variableenvaris set to one of the values listed in the space-separated value list. Ifenvaris not set, 'units' prints an error message and ignores the block of definitions.!varnotenvarvalue-listLoad the block of definitions that follows only if the environ- ment variableenvaris set to value that isnotlisted in the space-separated value list. Ifenvaris not set, 'units' prints an error message and ignores the block of definitions.GNU FREE DOCUMENTATION LICENSEFILES/usr/local/share/units/definitions.units -- the standard units data fileAUTHOR16 October 2017 UNITS(1)

NAME | SYNOPSIS | DESCRIPTION | USING

*UNITS*NON-INTERACTIVELY | UNIT DEFINITIONS | UNIT EXPRESSIONS | NONLINEAR UNIT CONVERSIONS | UNIT LISTS: CONVERSION TO SUMS OF UNITS | LOGGING CALCULATIONS | ADDING YOUR OWN DEFINITIONS | NUMERIC OUTPUT FORMAT | LOCALIZATION | ENVIRONMENT VARIABLES | DATA FILES | UNICODE SUPPORT | READLINE SUPPORT | UPDATING CURRENCY EXCHANGE RATES | DATABASE COMMAND SYNTAX | GNU FREE DOCUMENTATION LICENSE | FILES | AUTHOR

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