1UNITS(1) General Commands Manual UNITS(1)
2
6 units — unit conversion and calculation program
7
9 'units' [options] [from-unit [to-unit]]
10
12 The 'units' program converts quantities expressed in various systems of
13 measurement to their equivalents in other systems of measurement. Like
14 many similar programs, it can handle multiplicative scale changes. It
15 can also handle nonlinear conversions such as Fahrenheit to Celsius;
16 see Temperature Conversions. The program can also perform conversions
17 from and to sums of units, such as converting between meters and feet
18 plus inches.
19 Basic operation is simple: you enter the units that you want to convert
21 from and the units that you want to convert to. You can use the pro‐
22 gram interactively with prompts, or you can use it from the command
23 line.
24 Beyond simple unit conversions, 'units' can be used as a general-pur‐
26 pose scientific calculator that keeps track of units in its calcula‐
27 tions. You can form arbitrary complex mathematical expressions of
28 dimensions including sums, products, quotients, powers, and even roots
29 of dimensions. Thus you can ensure accuracy and dimensional consis‐
30 tency when working with long expressions that involve many different
31 units that may combine in complex ways; for an illustration, see Com‐
32 plicated Unit Expressions.
33 The units are defined in an external data file. You can use the exten‐
35 sive data file that comes with this program, or you can provide your
36 own data file to suit your needs. You can also use your own data file
37 to supplement the standard data file.
38 You can change the default behavior of 'units' with various options
40 given on the command line. See Invoking Units for a description of the
41 available options.
42
44 To invoke units for interactive use, type 'units' at your shell prompt.
45 The program will print something like this:
46 Currency exchange rates from www.timegenie.com on 2014-03-05
48 2860 units, 109 prefixes, 85 nonlinear units
49 You have:
51 At the 'You have:' prompt, type the quantity and units that you are
53 converting from. For example, if you want to convert ten meters to
54 feet, type '10 meters'. Next, 'units' will print 'You want:'. You
55 should type the units you want to convert to. To convert to feet, you
56 would type 'feet'. If the 'readline' library was compiled in then tab
57 will complete unit names. See Readline Support for more information
58 about 'readline'. To quit the program under Unix, press Ctrl-C or
59 Ctrl-D. Under Windows, press Ctrl-C or Ctrl-Z; with the latter, you may
60 also need to press Enter.
61 The result will be displayed in two ways. The first line of output,
63 which is marked with a '*' to indicate multiplication, gives the result
64 of the conversion you have asked for. The second line of output, which
65 is marked with a '/' to indicate division, gives the inverse of the
66 conversion factor. If you convert 10 meters to feet, 'units' will
67 print
68 * 32.808399
70 / 0.03048
71 which tells you that 10 meters equals about 32.8 feet. The second num‐
73 ber gives the conversion in the opposite direction. In this case, it
74 tells you that 1 foot is equal to about 0.03 dekameters since the
75 dekameter is 10 meters. It also tells you that 1/32.8 is about 0.03.
76 The 'units' program prints the inverse because sometimes it is a more
78 convenient number. In the example above, for example, the inverse
79 value is an exact conversion: a foot is exactly 0.03048 dekameters.
80 But the number given the other direction is inexact.
81 If you convert grains to pounds, you will see the following:
83 You have: grains
85 You want: pounds
86 * 0.00014285714
87 / 7000
88 From the second line of the output you can immediately see that a
90 grain is equal to a seven thousandth of a pound. This is not so obvi‐
91 ous from the first line of the output. If you find the output format
92 confusing, try using the '--verbose' option:
93 You have: grain
95 You want: aeginamina
96 grain = 0.00010416667 aeginamina
97 grain = (1 / 9600) aeginamina
98 If you request a conversion between units that measure reciprocal
100 dimensions, then 'units' will display the conversion results with an
101 extra note indicating that reciprocal conversion has been done:
102 You have: 6 ohms
104 You want: siemens
105 reciprocal conversion
106 * 0.16666667
107 / 6
108 Reciprocal conversion can be suppressed by using the '--strict' option.
110 As usual, use the '--verbose' option to get more comprehensible output:
111 You have: tex
113 You want: typp
114 reciprocal conversion
115 1 / tex = 496.05465 typp
116 1 / tex = (1 / 0.0020159069) typp
117 You have: 20 mph
119 You want: sec/mile
120 reciprocal conversion
121 1 / 20 mph = 180 sec/mile
122 1 / 20 mph = (1 / 0.0055555556) sec/mile
123 If you enter incompatible unit types, the 'units' program will print a
125 message indicating that the units are not conformable and it will dis‐
126 play the reduced form for each unit:
127 You have: ergs/hour
129 You want: fathoms kg^2 / day
130 conformability error
131 2.7777778e-11 kg m^2 / sec^3
132 2.1166667e-05 kg^2 m / sec
133 If you only want to find the reduced form or definition of a unit, sim‐
135 ply press Enter at the 'You want:' prompt. Here is an example:
136 You have: jansky
138 You want:
139 Definition: fluxunit = 1e-26 W/m^2 Hz = 1e-26 kg / s^2
140 The output from 'units' indicates that the jansky is defined to be
142 equal to a fluxunit which in turn is defined to be a certain combina‐
143 tion of watts, meters, and hertz. The fully reduced (and in this case
144 somewhat more cryptic) form appears on the far right.
145 Some named units are treated as dimensionless in some situations.
147 These units include the radian and steradian. These units will be
148 treated as equal to 1 in units conversions. Power is equal to torque
149 times angular velocity. This conversion can only be performed if the
150 radian is dimensionless.
151 You have: (14 ft lbf) (12 radians/sec)
153 You want: watts
154 * 227.77742
155 / 0.0043902509
156 It is also possible to compute roots and other non-integer powers of
158 dimensionless units; this allows computations such as the altitude of
159 geosynchronous orbit:
160 You have: cuberoot(G earthmass / (circle/siderealday)^2) - earthradius
162 You want: miles
163 * 22243.267
164 / 4.4957425e-05
165 Named dimensionless units are not treated as dimensionless in other
167 contexts. They cannot be used as exponents so for example,
168 'meter^radian' is forbidden.
169 If you want a list of options you can type '?' at the 'You want:'
171 prompt. The program will display a list of named units that are con‐
172 formable with the unit that you entered at the 'You have:' prompt
173 above. Conformable unit combinations will not appear on this list.
174 Typing 'help' at either prompt displays a short help message. You can
176 also type 'help' followed by a unit name. This will invoke a pager on
177 the units data base at the point where that unit is defined. You can
178 read the definition and comments that may give more details or histori‐
179 cal information about the unit. (You can generally quit out of the
180 page by pressing 'q'.)
181 Typing 'search' text will display a list of all of the units whose
183 names contain text as a substring along with their definitions. This
184 may help in the case where you aren't sure of the right unit name.
185
187 The 'units' program can perform units conversions non-interactively
188 from the command line. To do this, type the command, type the original
189 unit expression, and type the new units you want. If a units expres‐
190 sion contains non-alphanumeric characters, you may need to protect it
191 from interpretation by the shell using single or double quote charac‐
192 ters.
193 If you type
195 units "2 liters" quarts
197 then 'units' will print
199 * 2.1133764
201 / 0.47317647
202 and then exit. The output tells you that 2 liters is about 2.1 quarts,
204 or alternatively that a quart is about 0.47 times 2 liters.
205 If the conversion is successful, then 'units' will return success
207 (zero) to the calling environment. If you enter non-conformable units
208 then 'units' will print a message giving the reduced form of each unit
209 and it will return failure (nonzero) to the calling environment.
210 When you invoke 'units' with only one argument, it will print out the
212 definition of the specified unit. It will return failure if the unit
213 is not defined and success if the unit is defined.
214
216 The conversion information is read from a units data file that is
217 called 'definitions.units' and is usually located in the
218 '/usr/share/units' directory. If you invoke 'units' with the '-V'
219 option, it will print the location of this file. The default file
220 includes definitions for all familiar units, abbreviations and metric
221 prefixes. It also includes many obscure or archaic units. Many common
222 spelled-out numbers (e.g., 'seventeen') are recognized.
223 Many constants of nature are defined, including these:
225 pi ratio of circumference to diameter
227 c speed of light
228 e charge on an electron
229 force acceleration of gravity
230 mole Avogadro's number
231 water pressure per unit height of water
232 Hg pressure per unit height of mercury
233 au astronomical unit
234 k Boltzman's constant
235 mu0 permeability of vacuum
236 epsilon0 permittivity of vacuum
237 G Gravitational constant
238 mach speed of sound
239 The standard data file includes atomic masses for all of the elements
241 and numerous other constants. Also included are the densities of vari‐
242 ous ingredients used in baking so that '2 cups flour_sifted' can be
243 converted to 'grams'. This is not an exhaustive list. Consult the
244 units data file to see the complete list, or to see the definitions
245 that are used.
246 The 'pound' is a unit of mass. To get force, multiply by the force
248 conversion unit 'force' or use the shorthand 'lbf'. (Note that 'g' is
249 already taken as the standard abbreviation for the gram.) The unit
250 'ounce' is also a unit of mass. The fluid ounce is 'fluidounce' or
251 'floz'. When British capacity units differ from their US counterparts,
252 such as the British Imperial gallon, the unit is defined both ways with
253 'br' and 'us' prefixes. Your locale settings will determine the value
254 of the unprefixed unit. Currency is prefixed with its country name:
255 'belgiumfranc', 'britainpound'.
256 When searching for a unit, if the specified string does not appear
258 exactly as a unit name, then the 'units' program will try to remove a
259 trailing 's', 'es'. Next units will replace a trailing 'ies' with 'y'.
260 If that fails, 'units' will check for a prefix. The database includes
261 all of the standard metric prefixes. Only one prefix is permitted per
262 unit, so 'micromicrofarad' will fail. However, prefixes can appear
263 alone with no unit following them, so 'micro*microfarad' will work, as
264 will 'micro microfarad'.
265 To find out which units and prefixes are available, read the standard
267 units data file, which is extensively annotated.
268 English Customary Units
270 English customary units differ in various ways in different regions.
271 In Britain a complex system of volume measurements featured different
272 gallons for different materials such as a wine gallon and ale gallon
273 that different by twenty percent. This complexity was swept away in
274 1824 by a reform that created an entirely new gallon, the British Impe‐
275 rial gallon defined as the volume occupied by ten pounds of water.
276 Meanwhile in the USA the gallon is derived from the 1707 Winchester
277 wine gallon, which is 231 cubic inches. These gallons differ by about
278 twenty percent. By default if 'units' runs in the 'en_GB' locale you
279 will get the British volume measures. If it runs in the 'en_US' locale
280 you will get the US volume measures. In other locales the default val‐
281 ues are the US definitions. If you wish to force different definitions
282 then set the environment variable 'UNITS_ENGLISH' to either 'US' or
283 'GB' to set the desired definitions independent of the locale.
284 Before 1959, the value of a yard (and other units of measure defined in
286 terms of it) differed slightly among English-speaking countries. In
287 1959, Australia, Canada, New Zealand, the United Kingdom, the United
288 States, and South Africa adopted the Canadian value of 1 yard =
289 0.9144 m (exactly), which was approximately halfway between the values
290 used by the UK and the US; it had the additional advantage of making
291 1 inch = 2.54 cm (exactly). This new standard was termed the Interna‐
292 tional Yard. Australia, Canada, and the UK then defined all customary
293 lengths in terms of the International Yard (Australia did not define
294 the furlong or rod); because many US land surveys were in terms of the
295 pre-1959 units, the US continued to define customary surveyors' units
296 (furlong, chain, rod, and link) in terms of the previous value for the
297 foot, which was termed the US survey foot. The US defined a US survey
298 mile as 5280 US survey feet, and defined a statute mile as a US survey
299 mile. The US values for these units differ from the international val‐
300 ues by about 2 ppm.
301 The 'units' program uses the international values for these units; the
303 US values can be obtained by using either the 'US' or the 'survey' pre‐
304 fix. In either case, the simple familiar relationships among the units
305 are maintained, e.g., 1 'furlong' = 660 'ft', and 1 'USfurlong' = 660
306 'USft', though the metric equivalents differ slightly between the two
307 cases. The 'US' prefix or the 'survey' prefix can also be used to
308 obtain the US survey mile and the value of the US yard prior to 1959,
309 e.g., 'USmile' or 'surveymile' (but not 'USsurveymile'). To get the US
310 value of the statute mile, use either 'USstatutemile' or 'USmile'.
311 Except for distances that extend over hundreds of miles (such as in the
313 US State Plane Coordinate System), the differences in the miles are
314 usually insignificant:
315 You have: 100 surveymile - 100 mile
317 You want: inch
318 * 12.672025
319 / 0.078913984
320 The pre-1959 UK values for these units can be obtained with the prefix
322 'UK'.
323 In the US, the acre is officially defined in terms of the US survey
325 foot, but 'units' uses a definition based on the international foot.
326 If you want the official US acre use 'USacre' and similarly use
327 'USacrefoot' for the official US version of that unit. The difference
328 between these units is about 4 parts per million.
329
331 Operators
332 You can enter more complicated units by combining units with operations
333 such as multiplication, division, powers, addition, subtraction, and
334 parentheses for grouping. You can use the customary symbols for these
335 operators when 'units' is invoked with its default options. Addition‐
336 ally, 'units' supports some extensions, including high priority multi‐
337 plication using a space, and a high priority numerical division opera‐
338 tor ('|') that can simplify some expressions.
339 You multiply units using a space or an asterisk ('*'). The next exam‐
341 ple shows both forms:
342 You have: arabicfoot * arabictradepound * force
344 You want: ft lbf
345 * 0.7296
346 / 1.370614
347 You can divide units using the slash ('/') or with 'per':
349 You have: furlongs per fortnight
351 You want: m/s
352 * 0.00016630986
353 / 6012.8727
354 You can use parentheses for grouping:
356 You have: (1/2) kg / (kg/meter)
358 You want: league
359 * 0.00010356166
360 / 9656.0833
361 White space surrounding operators is optional, so the previous example
363 could have used '(1/2)kg/(kg/meter)'. As a consequence, however,
364 hyphenated spelled-out numbers (e.g., 'forty-two') cannot be used;
365 'forty-two' is interpreted as '40 - 2'.
366 Multiplication using a space has a higher precedence than division
368 using a slash and is evaluated left to right; in effect, the first '/'
369 character marks the beginning of the denominator of a unit expression.
370 This makes it simple to enter a quotient with several terms in the
371 denominator: 'J / mol K'. The '*' and '/' operators have the same
372 precedence, and are evaluated left to right; if you multiply with '*',
373 you must group the terms in the denominator with parentheses:
374 'J / (mol * K)'.
375 The higher precedence of the space operator may not always be advanta‐
377 geous. For example, 'm/s s/day' is equivalent to 'm / s s day' and has
378 dimensions of length per time cubed. Similarly, '1/2 meter' refers to
379 a unit of reciprocal length equivalent to 0.5/meter, perhaps not what
380 you would intend if you entered that expression. The get a half meter
381 you would need to use parentheses: '(1/2) meter'. The '*' operator is
382 convenient for multiplying a sequence of quotients. For example,
383 'm/s * s/day' is equivalent to 'm/day'. Similarly, you could write
384 '1/2 * meter' to get half a meter.
385 The 'units' program supports another option for numerical fractions:
387 you can indicate division of numbers with the vertical bar ('|'), so if
388 you wanted half a meter you could write '1|2 meter'. You cannot use
389 the vertical bar to indicate division of non-numerical units (e.g.,
390 'm|s' results in an error message).
391 Powers of units can be specified using the '^' character, as shown in
393 the following example, or by simple concatenation of a unit and its
394 exponent: 'cm3' is equivalent to 'cm^3'; if the exponent is more than
395 one digit, the '^' is required. You can also use '**' as an exponent
396 operator.
397 You have: cm^3
399 You want: gallons
400 * 0.00026417205
401 / 3785.4118
402 Concatenation only works with a single unit name: if you write
404 '(m/s)2', 'units' will treat it as multiplication by 2. When a unit
405 includes a prefix, exponent operators apply to the combination, so
406 'centimeter3' gives cubic centimeters. If you separate the prefix from
407 the unit with any multiplication operator (e.g., 'centi meter^3'), the
408 prefix is treated as a separate unit, so the exponent applies only to
409 the unit without the prefix. The second example is equivalent to
410 'centi * (meter^3)', and gives a hundredth of a cubic meter, not a
411 cubic centimeter. The 'units' program is limited internally to prod‐
412 ucts of 99 units; accordingly, expressions like 'meter^100' or
413 'joule^34' (represented internally as 'kg^34 m^68 / s^68') will fail.
414 The '|' operator has the highest precedence, so you can write the
416 square root of two thirds as '2|3^1|2'. The '^' operator has the sec‐
417 ond highest precedence, and is evaluated right to left, as usual:
418 You have: 5 * 2^3^2
420 You want:
421 Definition: 2560
422 With a dimensionless base unit, any dimensionless exponent is meaning‐
424 ful (e.g., 'pi^exp(2.371)'). Even though angle is sometimes treated as
425 dimensionless, exponents cannot have dimensions of angle:
426 You have: 2^radian
428 ^
429 Exponent not dimensionless
430 If the base unit is not dimensionless, the exponent must be a rational
432 number p/q, and the dimension of the unit must be a power of q, so
433 'gallon^2|3' works but 'acre^2|3' fails. An exponent using the slash
434 ('/') operator (e.g., 'gallon^(2/3)') is also acceptable; the parenthe‐
435 ses are needed because the precedence of '^' is higher than that of
436 '/'. Since 'units' cannot represent dimensions with exponents greater
437 than 99, a fully reduced exponent must have q < 100. When raising a
438 non-dimensionless unit to a power, 'units' attempts to convert a deci‐
439 mal exponent to a rational number with q < 100. If this is not possi‐
440 ble 'units' displays an error message:
441 You have: ft^1.234
443 Base unit not dimensionless; rational exponent required
444 A decimal exponent must match its rational representation to machine
446 precision, so 'acre^1.5' works but 'gallon^0.666' does not.
447 Sums and Differences of Units
449 You may sometimes want to add values of different units that are out‐
450 side the SI. You may also wish to use 'units' as a calculator that
451 keeps track of units. Sums of conformable units are written with the
452 '+' character, and differences with the '-' character.
453 You have: 2 hours + 23 minutes + 32 seconds
455 You want: seconds
456 * 8612
457 / 0.00011611705
458 You have: 12 ft + 3 in
460 You want: cm
461 * 373.38
462 / 0.0026782366
463 You have: 2 btu + 450 ft lbf
465 You want: btu
466 * 2.5782804
467 / 0.38785542
468 The expressions that are added or subtracted must reduce to identical
470 expressions in primitive units, or an error message will be displayed:
471 You have: 12 printerspoint - 4 heredium
473 ^
474 Illegal sum of non-conformable units
475 As usual, the precedence for '+' and '-' is lower than that of the
477 other operators. A fractional quantity such as 2 1/2 cups can be given
478 as '(2+1|2) cups'; the parentheses are necessary because multiplication
479 has higher precedence than addition. If you omit the parentheses,
480 'units' attempts to add '2' and '1|2 cups', and you get an error mes‐
481 sage:
482 You have: 2+1|2 cups
484 ^
485 Illegal sum or difference of non-conformable units
486 The expression could also be correctly written as '(2+1/2) cups'. If
488 you write '2 1|2 cups' the space is interpreted as multiplication so
489 the result is the same as '1 cup'.
490 The '+' and '-' characters sometimes appears in exponents like
492 '3.43e+8'. This leads to an ambiguity in an expression like '3e+2 yC'.
493 The unit 'e' is a small unit of charge, so this can be regarded as
494 equivalent to '(3e+2) yC' or '(3 e)+(2 yC)'. This ambiguity is
495 resolved by always interpreting '+' and '-' as part of an exponent if
496 possible.
497 Numbers as Units
499 For 'units', numbers are just another kind of unit. They can appear as
500 many times as you like and in any order in a unit expression. For
501 example, to find the volume of a box that is 2 ft by 3 ft by 12 ft in
502 steres, you could do the following:
503 You have: 2 ft 3 ft 12 ft
505 You want: stere
506 * 2.038813
507 / 0.49048148
508 You have: $ 5 / yard
510 You want: cents / inch
511 * 13.888889
512 / 0.072
513 And the second example shows how the dollar sign in the units conver‐
515 sion can precede the five. Be careful: 'units' will interpret '$5'
516 with no space as equivalent to 'dollar^5'.
517 Built-in Functions
519 Several built-in functions are provided: 'sin', 'cos', 'tan', 'ln',
520 'log', 'log2', 'exp', 'acos', 'atan' and 'asin'. The 'sin', 'cos', and
521 'tan' functions require either a dimensionless argument or an argument
522 with dimensions of angle.
523 You have: sin(30 degrees)
525 You want:
526 Definition: 0.5
527 You have: sin(pi/2)
529 You want:
530 Definition: 1
531 You have: sin(3 kg)
533 ^
534 Unit not dimensionless
535 The other functions on the list require dimensionless arguments. The
537 inverse trigonometric functions return arguments with dimensions of
538 angle.
539 If you wish to take roots of units, you may use the 'sqrt' or
541 'cuberoot' functions. These functions require that the argument have
542 the appropriate root. You can obtain higher roots by using fractional
543 exponents:
544 You have: sqrt(acre)
546 You want: feet
547 * 208.71074
548 / 0.0047913202
549 You have: (400 W/m^2 / stefanboltzmann)^(1/4)
551 You have:
552 Definition: 289.80882 K
553 You have: cuberoot(hectare)
555 ^
556 Unit not a root
557 Previous Result
559 You can insert the result of the previous conversion using the under‐
560 score ('_'). It is useful when you want to convert the same input to
561 several different units, for example
562 You have: 2.3 tonrefrigeration
564 You want: btu/hr
565 * 27600
566 / 3.6231884e-005
567 You have: _
568 You want: kW
569 * 8.0887615
570 / 0.12362832
571 Suppose you want to do some deep frying that requires an oil depth of
573 2 inches. You have 1/2 gallon of oil, and want to know the largest-
574 diameter pan that will maintain the required depth. The nonlinear unit
575 'circlearea' gives the radius of the circle (see Other Nonlinear Units,
576 for a more detailed description) in SI units; you want the diameter in
577 inches:
578 You have: 1|2 gallon / 2 in
580 You want: circlearea
581 0.10890173 m
582 You have: 2 _
583 You want: in
584 * 8.5749393
585 / 0.1166189
586 In most cases, surrounding white space is optional, so the previous
588 example could have used '2_'. If '_' follows a non-numerical unit sym‐
589 bol, however, the space is required:
590 You have: m_
592 ^
593 Parse error
594 When '_' is followed by a digit, the operation is multiplication rather
596 than exponentiation, so that '_2', is equivalent to '_ * 2' rather than
597 '_^2'.
598 You can use the '_' symbol any number of times; for example,
600 You have: m
602 You want:
603 Definition: 1 m
604 You have: _ _
605 You want:
606 Definition: 1 m^2
607 Using '_' before a conversion has been performed (e.g., immediately
609 after invocation) generates an error:
610 You have: _
612 ^
613 No previous result; '_' not set
614 Accordingly, '_' serves no purpose when 'units' is invoked non-interac‐
616 tively.
617 If 'units' is invoked with the '--verbose' option (see Invoking Units),
619 the value of '_' is not expanded:
620 You have: mile
622 You want: ft
623 mile = 5280 ft
624 mile = (1 / 0.00018939394) ft
625 You have: _
626 You want: m
627 _ = 1609.344 m
628 _ = (1 / 0.00062137119) m
629 You can give '_' at the 'You want:' prompt, but it usually is not very
631 useful.
632 Complicated Unit Expressions
634 The 'units' program is especially helpful in ensuring accuracy and
635 dimensional consistency when converting lengthy unit expressions. For
636 example, one form of the Darcy-Weisbach fluid-flow equation is
637 Delta P = (8 / pi)^2 (rho fLQ^2) / d^5,
639 where Delta P is the pressure drop, rho is the mass density, f is the
641 (dimensionless) friction factor, L is the length of the pipe, Q is the
642 volumetric flow rate, and d is the pipe diameter. It might be desired
643 to have the equation in the form
644 Delta P = A1 rho fLQ^2 / d^5
646 that accepted the user's normal units; for typical units used in the
648 US, the required conversion could be something like
649 You have: (8/pi^2)(lbm/ft^3)ft(ft^3/s)^2(1/in^5)
651 You want: psi
652 * 43.533969
653 / 0.022970568
654 The parentheses allow individual terms in the expression to be entered
656 naturally, as they might be read from the formula. Alternatively, the
657 multiplication could be done with the '*' rather than a space; then
658 parentheses are needed only around 'ft^3/s' because of its exponent:
659 You have: 8/pi^2 * lbm/ft^3 * ft * (ft^3/s)^2 /in^5
661 You want: psi
662 * 43.533969
663 / 0.022970568
664 Without parentheses, and using spaces for multiplication, the previous
666 conversion would need to be entered as
667 You have: 8 lb ft ft^3 ft^3 / pi^2 ft^3 s^2 in^5
669 You want: psi
670 * 43.533969
671 / 0.022970568
672 Backwards Compatibility:
674 '*' and '-' The original 'units' assigned multiplication a higher
675 precedence than division using the slash. This differs from the usual
676 precedence rules, which give multiplication and division equal prece‐
677 dence, and can be confusing for people who think of units as a calcula‐
678 tor.
679 The star operator ('*') included in this 'units' program has, by
681 default, the same precedence as division, and hence follows the usual
682 precedence rules. For backwards compatibility you can invoke 'units'
683 with the '--oldstar' option. Then '*' has a higher precedence than
684 division, and the same precedence as multiplication using the space.
685 Historically, the hyphen ('-') has been used in technical publications
687 to indicate products of units, and the original 'units' program treated
688 it as a multiplication operator. Because 'units' provides several
689 other ways to obtain unit products, and because '-' is a subtraction
690 operator in general algebraic expressions, 'units' treats the binary
691 '-' as a subtraction operator by default. For backwards compatibility
692 use the '--product' option, which causes 'units' to treat the binary
693 '-' operator as a product operator. When '-' is a multiplication oper‐
694 ator it has the same precedence as multiplication with a space, giving
695 it a higher precedence than division.
696 When '-' is used as a unary operator it negates its operand. Regard‐
698 less of the 'units' options, if '-' appears after '(' or after '+' then
699 it will act as a negation operator. So you can always compute 20
700 degrees minus 12 minutes by entering '20 degrees + -12 arcmin'. You
701 must use this construction when you define new units because you cannot
702 know what options will be in force when your definition is processed.
703
705 Nonlinear units are represented using functional notation. They make
706 possible nonlinear unit conversions such as temperature.
707 Temperature Conversions
709 Conversions between temperatures are different from linear conversions
710 between temperature increments—see the example below. The absolute
711 temperature conversions are handled by units starting with 'temp', and
712 you must use functional notation. The temperature-increment conver‐
713 sions are done using units starting with 'deg' and they do not require
714 functional notation.
715 You have: tempF(45)
717 You want: tempC
718 7.2222222
719 You have: 45 degF
721 You want: degC
722 * 25
723 / 0.04
724 Think of 'tempF(x)' not as a function but as a notation that indicates
726 that x should have units of 'tempF' attached to it. See Defining Non‐
727 linear Units. The first conversion shows that if it's 45 degrees
728 Fahrenheit outside, it's 7.2 degrees Celsius. The second conversion
729 indicates that a change of 45 degrees Fahrenheit corresponds to a
730 change of 25 degrees Celsius. The conversion from 'tempF(x)' is to
731 absolute temperature, so that
732 You have: tempF(45)
734 You want: degR
735 * 504.67
736 / 0.0019814929
737 gives the same result as
739 You have: tempF(45)
741 You want: tempR
742 * 504.67
743 / 0.0019814929
744 But if you convert 'tempF(x)' to 'degC', the output is probably not
746 what you expect:
747 You have: tempF(45)
749 You want: degC
750 * 280.37222
751 / 0.0035666871
752 The result is the temperature in K, because 'degC' is defined as 'K',
754 the Kelvin. For consistent results, use the 'tempX' units when convert‐
755 ing to a temperature rather than converting a temperature increment.
756 The 'tempC()' and 'tempF()' definitions are limited to positive abso‐
758 lute temperatures, and giving a value that would result in a negative
759 absolute temperature generates an error message:
760 You have: tempC(-275)
762 ^
763 Argument of function outside domain
764 ^
765 Other Nonlinear Units
767 Some other examples of nonlinear units are numerous different ring
768 sizes and wire gauges, the grit sizes used for abrasives, the decibel
769 scale, shoe size, scales for the density of sugar (e.g., baume). The
770 standard data file also supplies units for computing the area of a cir‐
771 cle and the volume of a sphere. See the standard units data file for
772 more details. Wire gauges with multiple zeroes are signified using
773 negative numbers where two zeroes is '-1'. Alternatively, you can use
774 the synonyms 'g00', 'g000', and so on that are defined in the standard
775 units data file.
776 You have: wiregauge(11)
778 You want: inches
779 * 0.090742002
780 / 11.020255
781 You have: brwiregauge(g00)
783 You want: inches
784 * 0.348
785 / 2.8735632
786 You have: 1 mm
788 You want: wiregauge
789 18.201919
790 You have: grit_P(600)
792 You want: grit_ansicoated
793 342.76923
794 The last example shows the conversion from P graded sand paper, which
796 is the European standard and may be marked ``P600'' on the back, to the
797 USA standard.
798 You can compute the area of a circle using the nonlinear unit,
800 'circlearea'. You can also do this using the circularinch or cir‐
801 cleinch. The next example shows two ways to compute the area of a cir‐
802 cle with a five inch radius and one way to compute the volume of a
803 sphere with a radius of one meter.
804 You have: circlearea(5 in)
806 You want: in2
807 * 78.539816
808 / 0.012732395
809 You have: 10^2 circleinch
811 You want: in2
812 * 78.539816
813 / 0.012732395
814 You have: spherevol(meter)
816 You want: ft3
817 * 147.92573
818 / 0.0067601492
819 The inverse of a nonlinear conversion is indicated by prefixing a tilde
821 ('~') to the nonlinear unit name:
822 You have: ~wiregauge(0.090742002 inches)
824 You want:
825 Definition: 11
826 You can give a nonlinear unit definition without an argument or paren‐
828 theses, and press Enter at the 'You want:' prompt to get the definition
829 of a nonlinear unit; if the definition is not valid for all real num‐
830 bers, the range of validity is also given. If the definition requires
831 specific units this information is also displayed:
832 You have: tempC
834 Definition: tempC(x) = x K + stdtemp
835 defined for x >= -273.15
836 You have: ~tempC
837 Definition: ~tempC(tempC) = (tempC +(-stdtemp))/K
838 defined for tempC >= 0 K
839 You have: circlearea
840 Definition: circlearea(r) = pi r^2
841 r has units m
842 To see the definition of the inverse use the '~' notation. In this
844 case the parameter in the functional definition will usually be the
845 name of the unit. Note that the inverse for 'tempC' shows that it
846 requires units of 'K' in the specification of the allowed range of val‐
847 ues. Nonlinear unit conversions are described in more detail in Defin‐
848 ing Nonlinear Units.
849
851 Outside of the SI, it is sometimes desirable to convert a single unit
852 to a sum of units—for example, feet to feet plus inches. The conver‐
853 sion from sums of units was described in Sums and Differences of Units,
854 and is a simple matter of adding the units with the '+' sign:
855 You have: 12 ft + 3 in + 3|8 in
857 You want: ft
858 * 12.28125
859 / 0.081424936
860 Although you can similarly write a sum of units to convert to, the
862 result will not be the conversion to the units in the sum, but rather
863 the conversion to the particular sum that you have entered:
864 You have: 12.28125 ft
866 You want: ft + in + 1|8 in
867 * 11.228571
868 / 0.089058524
869 The unit expression given at the 'You want:' prompt is equivalent to
871 asking for conversion to multiples of '1 ft + 1 in + 1|8 in', which is
872 1.09375 ft, so the conversion in the previous example is equivalent to
873 You have: 12.28125 ft
875 You want: 1.09375 ft
876 * 11.228571
877 / 0.089058524
878 In converting to a sum of units like miles, feet and inches, you typi‐
880 cally want the largest integral value for the first unit, followed by
881 the largest integral value for the next, and the remainder converted to
882 the last unit. You can do this conversion easily with 'units' using a
883 special syntax for lists of units. You must list the desired units in
884 order from largest to smallest, separated by the semicolon (';') char‐
885 acter:
886 You have: 12.28125 ft
888 You want: ft;in;1|8 in
889 12 ft + 3 in + 3|8 in
890 The conversion always gives integer coefficients on the units in the
892 list, except possibly the last unit when the conversion is not exact:
893 You have: 12.28126 ft
895 You want: ft;in;1|8 in
896 12 ft + 3 in + 3.00096 * 1|8 in
897 The order in which you list the units is important:
899 You have: 3 kg
901 You want: oz;lb
902 105 oz + 0.051367866 lb
903 You have: 3 kg
905 You want: lb;oz
906 6 lb + 9.8218858 oz
907 Listing ounces before pounds produces a technically correct result, but
909 not a very useful one. You must list the units in descending order of
910 size in order to get the most useful result.
911 Ending a unit list with the separator ';' has the same effect as
913 repeating the last unit on the list, so 'ft;in;1|8 in;' is equivalent
914 to 'ft;in;1|8 in;1|8 in'. With the example above, this gives
915 You have: 12.28126 ft
917 You want: ft;in;1|8 in;
918 12 ft + 3 in + 3|8 in + 0.00096 * 1|8 in
919 in effect separating the integer and fractional parts of the coeffi‐
921 cient for the last unit. If you instead prefer to round the last coef‐
922 ficient to an integer you can do this with the '--round' ('-r') option.
923 With the previous example, the result is
924 You have: 12.28126 ft
926 You want: ft;in;1|8 in
927 12 ft + 3 in + 3|8 in (rounded down to nearest 1|8 in)
928 When you use the '-r' option, repeating the last unit on the list has
930 no effect (e.g., 'ft;in;1|8 in;1|8 in' is equivalent to 'ft;in;1|8
931 in'), and hence neither does ending a list with a ';'. With a single
932 unit and the '-r' option, a terminal ';' does have an effect: it causes
933 'units' to treat the single unit as a list and produce a rounded value
934 for the single unit. Without the extra ';', the '-r' option has no
935 effect on single unit conversions. This example shows the output using
936 the '-r' option:
937 You have: 12.28126 ft
939 You want: in
940 * 147.37512
941 / 0.0067854058
942 You have: 12.28126 ft
944 You want: in;
945 147 in (rounded down to nearest in)
946 Each unit that appears in the list must be conformable with the first
948 unit on the list, and of course the listed units must also be conform‐
949 able with the unit that you enter at the 'You have:' prompt.
950 You have: meter
952 You want: ft;kg
953 ^
954 conformability error
955 ft = 0.3048 m
956 kg = 1 kg
957 You have: meter
959 You want: lb;oz
960 conformability error
961 1 m
962 0.45359237 kg
963 In the first case, 'units' reports the disagreement between units
965 appearing on the list. In the second case, 'units' reports disagree‐
966 ment between the unit you entered and the desired conversion. This
967 conformability error is based on the first unit on the unit list.
968 Other common candidates for conversion to sums of units are angles and
970 time:
971 You have: 23.437754 deg
973 You want; deg;arcmin;arcsec
974 23 deg + 26 arcmin + 15.9144 arcsec
975 You have: 7.2319 hr
977 You want: hr;min;sec
978 7 hr + 13 min + 54.84 sec
979 In North America, recipes for cooking typically measure ingredients by
981 volume, and use units that are not always convenient multiples of each
982 other. Suppose that you have a recipe for 6 and you wish to make a
983 portion for 1. If the recipe calls for 2 1/2 cups of an ingredient,
984 you might wish to know the measurements in terms of measuring devices
985 you have available, you could use 'units' and enter
986 You have: (2+1|2) cup / 6
988 You want: cup;1|2 cup;1|3 cup;1|4 cup;tbsp;tsp;1|2 tsp;1|4 tsp
989 1|3 cup + 1 tbsp + 1 tsp
990 By default, if a unit in a list begins with fraction of the form 1|x
992 and its multiplier is an integer, the fraction is given as the product
993 of the multiplier and the numerator; for example,
994 You have: 12.28125 ft
996 You want: ft;in;1|8 in;
997 12 ft + 3 in + 3|8 in
998 In many cases, such as the example above, this is what is wanted, but
1000 sometimes it is not. For example, a cooking recipe for 6 might call
1001 for 5 1/4 cup of an ingredient, but you want a portion for 2, and your
1002 1-cup measure is not available; you might try
1003 You have: (5+1|4) cup / 3
1005 You want: 1|2 cup;1|3 cup;1|4 cup
1006 3|2 cup + 1|4 cup
1007 This result might be fine for a baker who has a 1 1/2-cup measure (and
1009 recognizes the equivalence), but it may not be as useful to someone
1010 with more limited set of measures, who does want to do additional cal‐
1011 culations, and only wants to know ``How many 1/2-cup measures to I need
1012 to add?'' After all, that's what was actually asked. With the
1013 '--show-factor' option, the factor will not be combined with a unity
1014 numerator, so that you get
1015 You have: (5+1|4) cup / 3
1017 You want: 1|2 cup;1|3 cup;1|4 cup
1018 3 * 1|2 cup + 1|4 cup
1019 A user-specified fractional unit with a numerator other than 1 is never
1021 overridden, however—if a unit list specifies '3|4 cup;1|2 cup', a
1022 result equivalent to 1 1/2 cups will always be shown as '2 * 3|4 cup'
1023 whether or not the '--show-factor' option is given.
1024 Some applications for unit lists may be less obvious. Suppose that you
1026 have a postal scale and wish to ensure that it's accurate at 1 oz, but
1027 have only metric calibration weights. You might try
1028 You have: 1 oz
1030 You want: 100 g;50 g; 20 g;10 g;5 g;2 g;1 g;
1031 20 g + 5 g + 2 g + 1 g + 0.34952312 * 1 g
1032 You might then place one each of the 20 g, 5 g, 2 g, and 1 g weights on
1034 the scale and hope that it indicates close to
1035 You have: 20 g + 5 g + 2 g + 1 g
1037 You want: oz;
1038 0.98767093 oz
1039 Appending ';' to 'oz' forces a one-line display that includes the unit;
1041 here the integer part of the result is zero, so it is not displayed.
1042 A unit list such as
1044 cup;1|2 cup;1|3 cup;1|4 cup;tbsp;tsp;1|2 tsp;1|4 tsp
1046 can be tedious to enter. The 'units' program provides shorthand names
1048 for some common combinations:
1049 hms hours, minutes, seconds
1051 dms angle: degrees, minutes, seconds
1052 time years, days, hours, minutes and seconds
1053 usvol US cooking volume: cups and smaller
1054 Using these shorthands, or unit list aliases, you can do the following
1056 conversions:
1057 You have: anomalisticyear
1059 You want: time
1060 1 year + 25 min + 3.4653216 sec
1061 You have: 1|6 cup
1062 You want: usvol
1063 2 tbsp + 2 tsp
1064 You cannot combine a unit list alias with other units: it must appear
1066 alone at the 'You want:' prompt.
1067 You can display the definition of a unit list alias by entering it at
1069 the 'You have:' prompt:
1070 You have: dms
1072 Definition: unit list, deg;arcmin;arcsec
1073 When you specify compact output with '--compact', '--terse' or '-t' and
1075 perform conversion to a unit list, 'units' lists the conversion factors
1076 for each unit in the list, separated by semicolons.
1077 You have: year
1079 You want: day;min;sec
1080 365;348;45.974678
1081 Unlike the case of regular output, zeros are included in this output
1083 list:
1084 You have: liter
1086 You want: cup;1|2 cup;1|4 cup;tbsp
1087 4;0;0;3.6280454
1088
1090 The '--log' option allows you to save the results of calculations in a
1091 file; this can be useful if you need a permanent record of your work.
1092 For example, the fluid-flow conversion in Complicated Unit Expressions,
1093 is lengthy, and if you were to use it in designing a piping system, you
1094 might want a record of it for the project file. If the interactive
1095 session
1096 # Conversion factor A1 for pressure drop
1098 # dP = A1 rho f L Q^2/d^5
1099 You have: (8/pi^2) (lbm/ft^3)ft(ft^3/s)^2(1/in^5) # Input units
1100 You want: psi
1101 * 43.533969
1102 / 0.022970568
1103 were logged, the log file would contain
1105 ### Log started Fri Oct 02 15:55:35 2015
1107 # Conversion factor A1 for pressure drop
1109 # dP = A1 rho f L Q^2/d^5
1110 From: (8/pi^2) (lbm/ft^3)ft(ft^3/s)^2(1/in^5) # Input units
1111 To: psi
1112 * 43.533969
1113 / 0.022970568
1114 The time is written to the log file when the file is opened.
1116 The use of comments can help clarify the meaning of calculations for
1118 the log. The log includes conformability errors between the units at
1119 the 'You have:' and 'You want:' prompts, but not other errors, includ‐
1120 ing lack of conformability of items in sums or differences or among
1121 items in a unit list. For example, a conversion between zenith angle
1122 and elevation angle could involve
1123 You have: 90 deg - (5 deg + 22 min + 9 sec)
1125 ^
1126 Illegal sum or difference of non-conformable units
1127 You have: 90 deg - (5 deg + 22 arcmin + 9 arcsec)
1128 You want: dms
1129 84 deg + 37 arcmin + 51 arcsec
1130 You have: _
1131 You want: deg
1132 * 84.630833
1133 / 0.011816024
1134 You have:
1135 The log file would contain
1137 From: 90 deg - (5 deg + 22 arcmin + 9 arcsec)
1139 To: deg;arcmin;arcsec
1140 84 deg + 37 arcmin + 51 arcsec
1141 From: _
1142 To: deg
1143 * 84.630833
1144 / 0.011816024
1145 The initial entry error (forgetting that minutes have dimension of
1147 time, and that arcminutes must be used for dimensions of angle) does
1148 not appear in the output. When converting to a unit list alias,
1149 'units' expands the alias in the log file.
1150 The 'From:' and 'To:' tags are written to the log file even if the
1152 '--quiet' option is given. If the log file exists when 'units' is
1153 invoked, the new results are appended to the log file. The time is
1154 written to the log file each time the file is opened. The '--log'
1155 option is ignored when 'units' is used non-interactively.
1156
1158 You invoke 'units' like this:
1159 units [options] [from-unit [to-unit]]
1161 If the from-unit and to-unit are omitted, the program will use interac‐
1163 tive prompts to determine which conversions to perform. See Interac‐
1164 tive Use. If both from-unit and to-unit are given, 'units' will print
1165 the result of that single conversion and then exit. If only from-unit
1166 appears on the command line, 'units' will display the definition of
1167 that unit and exit. Units specified on the command line may need to be
1168 quoted to protect them from shell interpretation and to group them into
1169 two arguments. See Command Line Use.
1170 The default behavior of 'units' can be changed by various options given
1172 on the command line. In most cases, the options may be given in either
1173 short form (a single '-' followed by a single character) or long form
1174 ('--' followed by a word or hyphen-separated words). Short-form
1175 options are cryptic but require less typing; long-form options require
1176 more typing but are more explanatory and may be more mnemonic. With
1177 long-form options you need only enter sufficient characters to uniquely
1178 identify the option to the program. For example, '--out %f' works, but
1179 '--o %f' fails because 'units' has other long options beginning with
1180 'o'. However, '--q' works because '--quiet' is the only long option
1181 beginning with 'q'.
1182 Some options require arguments to specify a value (e.g., '-d 12' or
1184 '--digits 12'). Short-form options that do not take arguments may be
1185 concatenated (e.g., '-erS' is equivalent to '-e -r -S'); the last
1186 option in such a list may be one that takes an argument (e.g.,
1187 '-ed 12'). With short-form options, the space between an option and
1188 its argument is optional (e.g., '-d12' is equivalent to '-d 12').
1189 Long-form options may not be concatenated, and the space between a
1190 long-form option and its argument is required. Short-form and long-
1191 form options may be intermixed on the command line. Options may be
1192 given in any order, but when incompatible options (e.g., '--output-
1193 format' and '--exponential') are given in combination, behavior is con‐
1194 trolled by the last option given. For example, '-o%.12f -e' gives
1195 exponential format with the default eight significant digits).
1196 The following options are available:
1198 -c, --check
1200 Check that all units and prefixes defined in the units data file
1201 reduce to primitive units. Print a list of all units that can‐
1202 not be reduced. Also display some other diagnostics about sus‐
1203 picious definitions in the units data file. Only definitions
1204 active in the current locale are checked. You should always run
1205 'units' with this option after modifying a units data file.
1206 --check-verbose, --verbose-check
1208 Like the '--check' option, this option prints a list of units
1209 that cannot be reduced. But to help find unit definitions that
1210 cause endless loops, it lists the units as they are checked. If
1211 'units' hangs, then the last unit to be printed has a bad defi‐
1212 nition. Only definitions active in the current locale are
1213 checked.
1214 -d ndigits, --digits ndigits
1216 Set the number of significant digits in the output to the value
1217 specified (which must be greater than zero). For example,
1218 '-d 12' sets the number of significant digits to 12. With expo‐
1219 nential output 'units' displays one digit to the left of the
1220 decimal point and eleven digits to the right of the decimal
1221 point. On most systems, the maximum number of internally mean‐
1222 ingful digits is 15; if you specify a greater number than your
1223 system's maximum, 'units' will print a warning and set the num‐
1224 ber to the largest meaningful value. To directly set the maxi‐
1225 mum value, give an argument of 'max' (e.g., '-d max'). Be
1226 aware, of course, that ``significant'' here refers only to the
1227 display of numbers; if results depend on physical constants not
1228 known to this precision, the physically meaningful precision may
1229 be less than that shown. The '--digits' option conflicts with
1230 the '--output-format' option.
1231 -e, --exponential
1233 Set the numeric output format to exponential (i.e., scientific
1234 notation), like that used in the Unix 'units' program. The
1235 default precision is eight significant digits (seven digits to
1236 the right of the decimal point); this can be changed with the
1237 '--digits' option. The '--exponential' option conflicts with
1238 the '--output-format' option.
1239 -o format, --output-format format
1241 This option affords complete control over the numeric output
1242 format using the specified format. The format is a single float‐
1243 ing point numeric format for the 'printf()' function in the C
1244 programming language. All compilers support the format types
1245 'g' and 'G' to specify significant digits, 'e' and 'E' for sci‐
1246 entific notation, and 'f' for fixed-point decimal. The ISO C99
1247 standard introduced the 'F' type for fixed-point decimal and the
1248 'a' and 'A' types for hexadecimal floating point; these types
1249 are allowed with compilers that support them. The default for‐
1250 mat is '%.8g'; for greater precision, you could specify
1251 '-o %.15g'. See Numeric Output Format and the documentation for
1252 'printf()' for more detailed descriptions of the format specifi‐
1253 cation. The '--output-format' option affords the greatest con‐
1254 trol of the output appearance, but requires at least rudimentary
1255 knowledge of the 'printf()' format syntax. If you don't want to
1256 bother with the 'printf()' syntax, you can specify greater pre‐
1257 cision more simply with the '--digits' option or select exponen‐
1258 tial format with '--exponential'. The '--output-format' option
1259 is incompatible with the '--exponential' and '--digits' options.
1260 -f filename, --file filename
1262 Instruct 'units' to load the units file filename. You can spec‐
1263 ify up to 25 units files on the command line. When you use this
1264 option, 'units' will load only the files you list on the command
1265 line; it will not load the standard file or your personal units
1266 file unless you explicitly list them. If filename is the empty
1267 string ('-f ""'), the default units file (or that specified by
1268 'UNITSFILE') will be loaded in addition to any others specified
1269 with '-f'.
1270 -L logfile, --log logfile
1272 Save the results of calculations in the file logfile; this can
1273 be useful if it is important to have a record of unit conver‐
1274 sions or other calculations that are to be used extensively or
1275 in a critical activity such as a program or design project. If
1276 logfile exits, the new results are appended to the file. This
1277 option is ignored when 'units' is used non-interactively. See
1278 Logging Calculations for a more detailed description and some
1279 examples.
1280 -H filename, --history filename
1282 Instruct 'units' to save history to filename, so that a record
1283 of your commands is available for retrieval across different
1284 'units' invocations. To prevent the history from being saved
1285 set filename to the empty string ('-H ""'). This option has no
1286 effect if readline is not available.
1287 -h, --help
1289 Print out a summary of the options for 'units'.
1290 -m, --minus
1292 Causes '-' to be interpreted as a subtraction operator. This is
1293 the default behavior.
1294 -p, --product
1296 Causes '-' to be interpreted as a multiplication operator when
1297 it has two operands. It will act as a negation operator when it
1298 has only one operand: '(-3)'. By default '-' is treated as a
1299 subtraction operator.
1300 --oldstar
1302 Causes '*' to have the old-style precedence, higher than the
1303 precedence of division so that '1/2*3' will equal '1/6'.
1304 --newstar
1306 Forces '*' to have the new (default) precedence that follows the
1307 usual rules of algebra: the precedence of '*' is the same as the
1308 precedence of '/', so that '1/2*3' will equal '3/2'.
1309 --compact
1311 Give compact output featuring only the conversion factor. This
1312 turns off the '--verbose' option.
1313 -q, --quiet, --silent
1315 Suppress prompting of the user for units and the display of sta‐
1316 tistics about the number of units loaded.
1317 -n, --nolists
1319 Disable conversion to unit lists.
1320 -r, --round
1322 When converting to a combination of units given by a unit list,
1323 round the value of the last unit in the list to the nearest
1324 integer.
1325 -S, --show-factor
1327 When converting to a combination of units specified in a list,
1328 always show a non-unity factor before a unit that begins with a
1329 fraction with a unity denominator. By default, if the unit in a
1330 list begins with fraction of the form 1|x and its multiplier is
1331 an integer other than 1, the fraction is given as the product of
1332 the multiplier and the numerator (e.g., '3|8 in' rather than '3
1333 * 1|8 in'). In some cases, this is not what is wanted; for
1334 example, the results for a cooking recipe might show '3 *
1335 1|2 cup' as '3|2 cup'. With the '--show-factor' option, a
1336 result equivalent to 1.5 cups will display as '3 * 1|2 cup'
1337 rather than '3|2 cup'. A user-specified fractional unit with a
1338 numerator other than 1 is never overridden, however—if a unit
1339 list specifies '3|4 cup;1|2 cup', a result equivalent to 1 1/2
1340 cups will always be shown as '2 * 3|4 cup' whether or not the
1341 '--show-factor' option is given.
1342 -s, --strict
1344 Suppress conversion of units to their reciprocal units. For
1345 example, 'units' will normally convert hertz to seconds because
1346 these units are reciprocals of each other. The strict option
1347 requires that units be strictly conformable to perform a conver‐
1348 sion, and will give an error if you attempt to convert hertz to
1349 seconds.
1350 -1, --one-line
1352 Give only one line of output (the forward conversion). Do not
1353 print the reverse conversion. If a reciprocal conversion is
1354 performed then 'units' will still print the ``reciprocal conver‐
1355 sion'' line.
1356 -t, --terse
1358 Give terse output when converting units. This option can be
1359 used when calling 'units' from another program so that the out‐
1360 put is easy to parse. This option has the combined effect of
1361 these options: '--strict' '--quiet' '--one-line' '--compact'.
1362 When combined with '--version' it produces a display showing
1363 only the program name and version number.
1364 -v, --verbose
1366 Give slightly more verbose output when converting units. When
1367 combined with the '-c' option this gives the same effect as
1368 '--check-verbose'. When combined with '--version' produces a
1369 more detailed output, equivalent to the '--info' option.
1370 -V, --version
1372 Print the program version number, tell whether the 'readline'
1373 library has been included, tell whether UTF-8 support has been
1374 included; give the locale, the location of the default units
1375 data file, and the location of the personal units data file;
1376 indicate if the personal units data file does not exist.
1377 When given in combination with the '--terse' option, the program prints
1379 only the version number and exits.
1380 When given in combination with the '--verbose' option, the program, the
1382 '--version' option has the same effect as the '--info' option below.
1383 -I, --info
1385 Print the information given with the '--version' option, show
1386 the pathname of the units program, show the status of the
1387 'UNITSFILE' and 'MYUNITSFILE' environment variables, and addi‐
1388 tional information about how 'units' locates the related files.
1389 On systems running Microsoft Windows, the status of the
1390 'UNITSLOCALE' environment variable and information about the
1391 related locale map are also given. This option is usually of
1392 interest only to developers and administrators, but it can some‐
1393 times be useful for troubleshooting.
1394 Combining the '--version' and '--verbose' options has the same effect
1396 as giving '--info'.
1397 -U, --unitsfile
1399 Print the location of the default units data file and exit; if
1400 the file cannot be found, print ``Units data file not found''.
1401 -l locale, --locale locale
1403 Print the information given with the '--version' option, show
1404 the Force a specified locale such as 'en_GB' to get British def‐
1405 initions by default. This overrides the locale determined from
1406 system settings or environment variables. See Locale for a
1407 description of locale format.
1408
1410 Units Data Files
1411 The units and prefixes that 'units' can convert are defined in the
1412 units data file, typically '/usr/share/units/definitions.units'. If
1413 you can't find this file, run 'units --version' to get information on
1414 the file locations for your installation. Although you can extend or
1415 modify this data file if you have appropriate user privileges, it's
1416 usually better to put extensions in separate files so that the defini‐
1417 tions will be preserved if you update 'units'.
1418 You can include additional data files in the units database using the
1420 '!include' command in the standard units data file. For example
1421 !include /usr/local/share/units/local.units
1423 might be appropriate for a site-wide supplemental data file. The loca‐
1425 tion of the '!include' statement in the standard units data file is
1426 important; later definitions replace earlier ones, so any definitions
1427 in an included file will override definitions before the '!include'
1428 statement in the standard units data file. With normal invocation, no
1429 warning is given about redefinitions; to ensure that you don't have an
1430 unintended redefinition, run 'units -c' after making changes to any
1431 units data file.
1432 If you want to add your own units in addition to or in place of stan‐
1434 dard or site-wide supplemental units data files, you can include them
1435 in the '.units' file in your home directory. If this file exists it is
1436 read after the standard units data file, so that any definitions in
1437 this file will replace definitions of the same units in the standard
1438 data file or in files included from the standard data file. This file
1439 will not be read if any units files are specified on the command line.
1440 (Under Windows the personal units file is named 'unitdef.units'.) Run‐
1441 ning 'units -V' will display the location and name of your personal
1442 units file.
1443 The 'units' program first tries to determine your home directory from
1445 the 'HOME' environment variable. On systems running Microsoft Windows,
1446 if 'HOME' does not exist, 'units' attempts to find your home directory
1447 from 'HOMEDRIVE', 'HOMEPATH' and 'USERPROFILE'. You can specify an
1448 arbitrary file as your personal units data file with the 'MYUNITSFILE'
1449 environment variable; if this variable exists, its value is used with‐
1450 out searching your home directory. The default units data files are
1451 described in more detail in Data Files.
1452 Defining New Units and Prefixes
1454 A unit is specified on a single line by giving its name and an equiva‐
1455 lence. Comments start with a '#' character, which can appear anywhere
1456 in a line. The backslash character ('\') acts as a continuation char‐
1457 acter if it appears as the last character on a line, making it possible
1458 to spread definitions out over several lines if desired. A file can be
1459 included by giving the command '!include' followed by the file's name.
1460 The '!' must be the first character on the line. The file will be
1461 sought in the same directory as the parent file unless you give a full
1462 path. The name of the file to be included cannot contain spaces or the
1463 comment character '#'.
1464 Unit names must not contain any of the operator characters '+', '-',
1466 '*', '/', '|', '^', ';', '~', the comment character '#', or parenthe‐
1467 ses. They cannot begin or end with an underscore ('_'), a comma (',')
1468 or a decimal point ('.'). The figure dash (U+2012), typographical
1469 minus (`-'; U+2212), and en dash (`-'; U+2013) are converted to the
1470 operator '-', so none of these characters can appear in unit names.
1471 Names cannot begin with a digit, and if a name ends in a digit other
1472 than zero, the digit must be preceded by a string beginning with an
1473 underscore, and afterwards consisting only of digits, decimal points,
1474 or commas. For example, 'foo_2', 'foo_2,1', or 'foo_3.14' are valid
1475 names but 'foo2' or 'foo_a2' are invalid. You could define nitrous
1476 oxide as
1477 N2O nitrogen 2 + oxygen
1479 but would need to define nitrogen dioxide as
1481 NO_2 nitrogen + oxygen 2
1483 Be careful to define new units in terms of old ones so that a reduction
1485 leads to the primitive units, which are marked with '!' characters.
1486 Dimensionless units are indicated by using the string '!dimensionless'
1487 for the unit definition.
1488 When adding new units, be sure to use the '-c' option to check that the
1490 new units reduce properly. If you create a loop in the units defini‐
1491 tions, then 'units' will hang when invoked with the '-c' option. You
1492 will need to use the '--check-verbose' option, which prints out each
1493 unit as it is checked. The program will still hang, but the last unit
1494 printed will be the unit that caused the infinite loop.
1495 If you define any units that contain '+' characters, carefully check
1497 them because the '-c' option will not catch non-conformable sums. Be
1498 careful with the '-' operator as well. When used as a binary operator,
1499 the '-' character can perform addition or multiplication depending on
1500 the options used to invoke 'units'. To ensure consistent behavior use
1501 '-' only as a unary negation operator when writing units definitions.
1502 To multiply two units leave a space or use the '*' operator with care,
1503 recalling that it has two possible precedence values and may require
1504 parentheses to ensure consistent behavior. To compute the difference
1505 of 'foo' and 'bar' write 'foo+(-bar)' or even 'foo+-bar'.
1506 Here is an example of a short data file that defines some basic units:
1508 m ! # The meter is a primitive unit
1510 sec ! # The second is a primitive unit
1511 rad !dimensionless # A dimensionless primitive unit
1512 micro- 1e-6 # Define a prefix
1513 minute 60 sec # A minute is 60 seconds
1514 hour 60 min # An hour is 60 minutes
1515 inch 0.0254 m # Inch defined in terms of meters
1516 ft 12 inches # The foot defined in terms of inches
1517 mile 5280 ft # And the mile
1518 A unit that ends with a '-' character is a prefix. If a prefix defini‐
1520 tion contains any '/' characters, be sure they are protected by paren‐
1521 theses. If you define 'half- 1/2' then 'halfmeter' would be equivalent
1522 to '1 / (2 meter)'.
1523 Defining Nonlinear Units
1525 Some unit conversions of interest are nonlinear; for example, tempera‐
1526 ture conversions between the Fahrenheit and Celsius scales cannot be
1527 done by simply multiplying by conversion factors.
1528 When you give a linear unit definition such as 'inch 2.54 cm' you are
1530 providing information that 'units' uses to convert values in inches
1531 into primitive units of meters. For nonlinear units, you give a func‐
1532 tional definition that provides the same information.
1533 Nonlinear units are represented using a functional notation. It is
1535 best to regard this notation not as a function call but as a way of
1536 adding units to a number, much the same way that writing a linear unit
1537 name after a number adds units to that number. Internally, nonlinear
1538 units are defined by a pair of functions that convert to and from lin‐
1539 ear units in the database, so that an eventual conversion to primitive
1540 units is possible.
1541 Here is an example nonlinear unit definition:
1543 tempF(x) units=[1;K] domain=[-459.67,) range=[0,) \
1545 (x+(-32)) degF + stdtemp ; (tempF+(-stdtemp))/degF + 32
1546 A nonlinear unit definition comprises a unit name, a formal parameter
1548 name, two functions, and optional specifications for units, the domain,
1549 and the range (the domain of the inverse function). The functions tell
1550 'units' how to convert to and from the new unit. To produce valid
1551 results, the arguments of these functions need to have the correct
1552 dimensions and be within the domains for which the functions are
1553 defined.
1554 The definition begins with the unit name followed immediately (with no
1556 spaces) by a '(' character. In the parentheses is the name of the for‐
1557 mal parameter. Next is an optional specification of the units required
1558 by the functions in the definition. In the example above, the
1559 'units=[1;K]' specification indicates that the 'tempF' function
1560 requires an input argument conformable with '1' (i.e., the argument is
1561 dimensionless), and that the inverse function requires an input argu‐
1562 ment conformable with 'K'. For normal nonlinear units definition, the
1563 forward function will always take a dimensionless argument; in general,
1564 the inverse function will need units that match the quantity measured
1565 by your nonlinear unit. Specifying the units enables 'units' to per‐
1566 form error checking on function arguments, and also to assign units to
1567 domain and range specifications, which are described later.
1568 Next the function definitions appear. In the example above, the
1570 'tempF' function is defined by
1571 tempF(x) = (x+(-32)) degF + stdtemp
1573 This gives a rule for converting 'x' in the units 'tempF' to linear
1575 units of absolute temperature, which makes it possible to convert from
1576 tempF to other units.
1577 To enable conversions to Fahrenheit, you must give a rule for the
1579 inverse conversions. The inverse will be 'x(tempF)' and its definition
1580 appears after a ';' character. In our example, the inverse is
1581 x(tempF) = (tempF+(-stdtemp))/degF + 32
1583 This inverse definition takes an absolute temperature as its argument
1585 and converts it to the Fahrenheit temperature. The inverse can be
1586 omitted by leaving out the ';' character and the inverse definition,
1587 but then conversions to the unit will not be possible. If the inverse
1588 definition is omitted, the '--check' option will display a warning. It
1589 is up to you to calculate and enter the correct inverse function to
1590 obtain proper conversions; the '--check' option tests the inverse at
1591 one point and prints an error if it is not valid there, but this is not
1592 a guarantee that your inverse is correct.
1593 With some definitions, the units may vary. For example, the definition
1595 square(x) x^2
1597 can have any arbitrary units, and can also take dimensionless argu‐
1599 ments. In such a case, you should not specify units. If a definition
1600 takes a root of its arguments, the definition is valid only for units
1601 that yield such a root. For example,
1602 squirt(x) sqrt(x)
1604 is valid for a dimensionless argument, and for arguments with even pow‐
1606 ers of units.
1607 Some definitions may not be valid for all real numbers. In such cases,
1609 'units' can handle errors better if you specify an appropriate domain
1610 and range. You specify the domain and range as shown below:
1611 baume(d) units=[1;g/cm^3] domain=[0,130.5] range=[1,10] \
1613 (145/(145-d)) g/cm^3 ; (baume+-g/cm^3) 145 / baume
1614 In this example the domain is specified after 'domain=' with the end‐
1616 points given in brackets. In accord with mathematical convention,
1617 square brackets indicate a closed interval (one that includes its end‐
1618 points), and parentheses indicate an open interval (one that does not
1619 include its endpoints). An interval can be open or closed on one or
1620 both ends; an interval that is unbounded on either end is indicated by
1621 omitting the limit on that end. For example, a quantity to which deci‐
1622 bel (dB) is applied may have any value greater than zero, so the range
1623 is indicated by '(0,)':
1624 decibel(x) units=[1;1] range=(0,) 10^(x/10); 10 log(decibel)
1626 If the domain or range is given, the second endpoint must be greater
1628 than the first.
1629 The domain and range specifications can appear independently and in any
1631 order along with the units specification. The values for the domain
1632 and range endpoints are attached to the units given in the units speci‐
1633 fication, and if necessary, the parameter value is adjusted for compar‐
1634 ison with the endpoints. For example, if a definition includes
1635 'units=[1;ft]' and 'range=[3,)', the range will be taken as 3 ft to
1636 infinity. If the function is passed a parameter of '900 mm', that
1637 value will be adjusted to 2.9527559 ft, which is outside the specified
1638 range. If you omit the units specification from the previous example,
1639 'units' can not tell whether you intend the lower endpoint to be 3 ft
1640 or 3 microfurlongs, and can not adjust the parameter value of 900 mm
1641 for comparison. Without units, numerical values other than zero or
1642 plus or minus infinity for domain or range endpoints are meaningless,
1643 and accordingly they are not allowed. If you give other values without
1644 units then the definition will be ignored and you will get an error
1645 message.
1646 Although the units, domain, and range specifications are optional, it's
1648 best to give them when they are applicable; doing so allows 'units' to
1649 perform better error checking and give more helpful error messages.
1650 Giving the domain and range also enables the '--check' option to find a
1651 point in the domain to use for its point check of your inverse defini‐
1652 tion.
1653 You can make synonyms for nonlinear units by providing both the forward
1655 and inverse functions; inverse functions can be obtained using the '~'
1656 operator. So to create a synonym for 'tempF' you could write
1657 fahrenheit(x) units=[1;K] tempF(x); ~tempF(fahrenheit)
1659 This is useful for creating a nonlinear unit definition that differs
1661 slightly from an existing definition without having to repeat the orig‐
1662 inal functions. For example,
1663 dBW(x) units=[1;W] range=[0,) dB(x) W ; ~dB(dBW/W)
1665 If you wish a synonym to refer to an existing nonlinear unit without
1667 modification, you can do so more simply by adding the synonym with
1668 appended parentheses as a new unit, with the existing nonlinear unit—
1669 without parentheses—as the definition. So to create a synonym for
1670 'tempF' you could write
1671 fahrenheit() tempF
1673 The definition must be a nonlinear unit; for example, the synonym
1675 fahrenheit() meter
1677 will result in an error message when 'units' starts.
1679 You may occasionally wish to define a function that operates on units.
1681 This can be done using a nonlinear unit definition. For example, the
1682 definition below provides conversion between radius and the area of a
1683 circle. This definition requires a length as input and produces an
1684 area as output, as indicated by the 'units=' specification. Specifying
1685 the range as the nonnegative numbers can prevent cryptic error mes‐
1686 sages.
1687 circlearea(r) units=[m;m^2] range=[0,) pi r^2 ; sqrt(circlearea/pi)
1689 Defining Piecewise Linear Units
1691 Sometimes you may be interested in a piecewise linear unit such as many
1692 wire gauges. Piecewise linear units can be defined by specifying con‐
1693 versions to linear units on a list of points. Conversion at other
1694 points will be done by linear interpolation. A partial definition of
1695 zinc gauge is
1696 zincgauge[in] 1 0.002, 10 0.02, 15 0.04, 19 0.06, 23 0.1
1698 In this example, 'zincgauge' is the name of the piecewise linear unit.
1700 The definition of such a unit is indicated by the embedded '[' charac‐
1701 ter. After the bracket, you should indicate the units to be attached
1702 to the numbers in the table. No spaces can appear before the ']' char‐
1703 acter, so a definition like 'foo[kg meters]' is invalid; instead write
1704 'foo[kg*meters]'. The definition of the unit consists of a list of
1705 pairs optionally separated by commas. This list defines a function for
1706 converting from the piecewise linear unit to linear units. The first
1707 item in each pair is the function argument; the second item is the
1708 value of the function at that argument (in the units specified in
1709 brackets). In this example, we define 'zincgauge' at five points. For
1710 example, we set 'zincgauge(1)' equal to '0.002 in'. Definitions like
1711 this may be more readable if written using continuation characters
1712 as
1713 zincgauge[in] \
1715 1 0.002 \
1716 10 0.02 \
1717 15 0.04 \
1718 19 0.06 \
1719 23 0.1
1720 With the preceding definition, the following conversion can be per‐
1722 formed:
1723 You have: zincgauge(10)
1725 You want: in
1726 * 0.02
1727 / 50
1728 You have: .01 inch
1729 You want: zincgauge
1730 5
1731 If you define a piecewise linear unit that is not strictly monotonic,
1733 then the inverse will not be well defined. If the inverse is requested
1734 for such a unit, 'units' will return the smallest inverse.
1735 After adding nonlinear units definitions, you should normally run
1737 'units --check' to check for errors. If the 'units' keyword is not
1738 given, the '--check' option checks a nonlinear unit definition using a
1739 dimensionless argument, and then checks using an arbitrary combination
1740 of units, as well as the square and cube of that combination; a warning
1741 is given if any of these tests fail. For example,
1742 Warning: function 'squirt(x)' defined as 'sqrt(x)'
1744 failed for some test inputs:
1745 squirt(7(kg K)^1): Unit not a root
1746 squirt(7(kg K)^3): Unit not a root
1747 Running 'units --check' will print a warning if a non-monotonic piece‐
1749 wise linear unit is encountered. For example, the relationship between
1750 ANSI coated abrasive designation and mean particle size is non-mono‐
1751 tonic in the vicinity of 800 grit:
1752 ansicoated[micron] \
1754 . . .
1755 600 10.55 \
1756 800 11.5 \
1757 1000 9.5 \
1758 Running 'units --check' would give the error message
1760 Table 'ansicoated' lacks unique inverse around entry 800
1762 Although the inverse is not well defined in this region, it's not
1764 really an error. Viewing such error messages can be tedious, and if
1765 there are enough of them, they can distract from true errors. Error
1766 checking for nonlinear unit definitions can be suppressed by giving the
1767 'noerror' keyword; for the examples above, this could be done as
1768 squirt(x) noerror domain=[0,) range=[0,) sqrt(x); squirt^2
1770 ansicoated[micron] noerror \
1771 . . .
1772 Use the 'noerror' keyword with caution. The safest approach after
1774 adding a nonlinear unit definition is to run 'units --check' and con‐
1775 firm that there are no actual errors before adding the 'noerror' key‐
1776 word.
1777 Defining Unit List Aliases
1779 Unit list aliases are treated differently from unit definitions,
1780 because they are a data entry shorthand rather than a true definition
1781 for a new unit. A unit list alias definition begins with '!unitlist'
1782 and includes the alias and the definition; for example, the aliases
1783 included in the standard units data file are
1784 !unitlist hms hr;min;sec
1786 !unitlist time year;day;hr;min;sec
1787 !unitlist dms deg;arcmin;arcsec
1788 !unitlist ftin ft;in;1|8 in
1789 !unitlist usvol cup;3|4 cup;2|3 cup;1|2 cup;1|3 cup;1|4 cup;\
1790 tbsp;tsp;1|2 tsp;1|4 tsp;1|8 tsp
1791 Unit list aliases are only for unit lists, so the definition must
1793 include a ';'. Unit list aliases can never be combined with units or
1794 other unit list aliases, so the definition of 'time' shown above could
1795 not have been shortened to 'year;day;hms'.
1796 As usual, be sure to run 'units --check' to ensure that the units
1798 listed in unit list aliases are conformable.
1799
1801 By default, 'units' shows results to eight significant digits. You can
1802 change this with the '--exponential', '--digits', and '--output-format'
1803 options. The first sets an exponential format (i.e., scientific nota‐
1804 tion) like that used in the original Unix 'units' program, the second
1805 allows you to specify a different number of significant digits, and the
1806 last allows you to control the output appearance using the format for
1807 the 'printf()' function in the C programming language. If you only
1808 want to change the number of significant digits or specify exponential
1809 format type, use the '--digits' and '--exponential' options. The
1810 '--output-format' option affords the greatest control of the output
1811 appearance, but requires at least rudimentary knowledge of the
1812 'printf()' format syntax. See Invoking Units for descriptions of these
1813 options.
1814 Format Specification
1816 The format specification recognized with the '--output-format' option
1817 is a subset of that for 'printf()'. The format specification has the
1818 form '%'[flags][width]['.'precision]type; it must begin with '%', and
1819 must end with a floating-point type specifier: 'g' or 'G' to specify
1820 the number of significant digits, 'e' or 'E' for scientific notation,
1821 and 'f' for fixed-point decimal. The ISO C99 standard added the 'F'
1822 type for fixed-point decimal and the 'a' and 'A' types for hexadecimal
1823 floating point; these types are allowed with compilers that support
1824 them. Type length modifiers (e.g., 'L' to indicate a long double) are
1825 inapplicable and are not allowed.
1826 The default format for 'units' is '%.8g'; for greater precision, you
1828 could specify '-o %.15g'. The 'g' and 'G' format types use exponential
1829 format whenever the exponent would be less than -4, so the value
1830 0.000013 displays as '1.3e-005'. These types also use exponential
1831 notation when the exponent is greater than or equal to the precision,
1832 so with the default format, the value 5e7 displays as '50000000' and
1833 the value 5e8 displays as '5e+008'. If you prefer fixed-point display,
1834 you might specify '-o %.8f'; however, small numbers will display very
1835 few significant digits, and values less than 0.5e-8 will show nothing
1836 but zeros.
1837 The format specification may include one or more optional flags: '+',
1839 ' ' (space), '#', '-', or '0' (the digit zero). The digit-grouping
1840 flag ''' is allowed with compilers that support it. Flags are followed
1841 by an optional value for the minimum field width, and an optional pre‐
1842 cision specification that begins with a period (e.g., '.6'). The field
1843 width includes the digits, decimal point, the exponent, thousands sepa‐
1844 rators (with the digit-grouping flag), and the sign if any of these are
1845 shown.
1846 Flags
1848 The '+' flag causes the output to have a sign ('+' or '-'). The space
1849 flag ' ' is similar to the '+' flag, except that when the value is pos‐
1850 itive, it is prefixed with a space rather than a plus sign; this flag
1851 is ignored if the '+' flag is also given. The '+' or ' ' flag could be
1852 useful if conversions might include positive and negative results, and
1853 you wanted to align the decimal points in exponential notation. The
1854 '#' flag causes the output value to contain a decimal point in all
1855 cases; by default, the output contains a decimal point only if there
1856 are digits (which can be trailing zeros) to the right of the point.
1857 With the 'g' or 'G' types, the '#' flag also prevents the suppression
1858 of trailing zeros. The digit-grouping flag ''' shows a thousands sepa‐
1859 rator in digits to the left of the decimal point. This can be useful
1860 when displaying large numbers in fixed-point decimal; for example, with
1861 the format '%f',
1862 You have: mile
1864 You want: microfurlong
1865 * 8000000.000000
1866 / 0.000000
1867 the magnitude of the first result may not be immediately obvious with‐
1869 out counting the digits to the left of the decimal point. If the thou‐
1870 sands separator is the comma (','), the output with the format '%'f'
1871 might be
1872 You have: mile
1874 You want: microfurlong
1875 * 8,000,000.000000
1876 / 0.000000
1877 making the magnitude readily apparent. Unfortunately, few compilers
1879 support the digit-grouping flag.
1880 With the '-' flag, the output value is left aligned within the speci‐
1882 fied field width. If a field width greater than needed to show the
1883 output value is specified, the '0' (zero) flag causes the output value
1884 to be left padded with zeros until the specified field width is
1885 reached; for example, with the format '%011.6f',
1886 You have: troypound
1888 You want: grain
1889 * 5760.000000
1890 / 0000.000174
1891 The '0' flag has no effect if the '-' (left align) flag is given.
1893 Field Width
1895 By default, the output value is left aligned and shown with the minimum
1896 width necessary for the specified (or default) precision. If a field
1897 width greater than this is specified, the value shown is right aligned,
1898 and padded on the left with enough spaces to provide the specified
1899 field width. A width specification is typically used with fixed-point
1900 decimal to have columns of numbers align at the decimal point; this
1901 arguably is less useful with 'units' than with long columnar output,
1902 but it may nonetheless assist in quickly assessing the relative magni‐
1903 tudes of results. For example, with the format '%12.6f',
1904 You have: km
1906 You want: in
1907 * 39370.078740
1908 / 0.000025
1909 You have: km
1910 You want: rod
1911 * 198.838782
1912 / 0.005029
1913 You have: km
1914 You want: furlong
1915 * 4.970970
1916 / 0.201168
1917 Precision
1919 The meaning of ``precision'' depends on the format type. With 'g' or
1920 'G', it specifies the number of significant digits (like the '--digits'
1921 option); with 'e', 'E', 'f', or 'F', it specifies the maximum number of
1922 digits to be shown after the decimal point.
1923 With the 'g' and 'G' format types, trailing zeros are suppressed, so
1925 the results may sometimes have fewer digits than the specified preci‐
1926 sion (as indicated above, the '#' flag causes trailing zeros to be dis‐
1927 played).
1928 The default precision is 6, so '%g' is equivalent to '%.6g', and would
1930 show the output to six significant digits. Similarly, '%e' or '%f'
1931 would show the output with six digits after the decimal point.
1932 The C 'printf()' function allows a precision of arbitrary size, whether
1934 or not all of the digits are meaningful. With most compilers, the max‐
1935 imum internal precision with 'units' is 15 decimal digits (or 13 hexa‐
1936 decimal digits). With the '--digits' option, you are limited to the
1937 maximum internal precision; with the '--output-format' option, you may
1938 specify a precision greater than this, but it may not be meaningful.
1939 In some cases, specifying excess precision can result in rounding arti‐
1940 facts. For example, a pound is exactly 7000 grains, but with the for‐
1941 mat '%.18g', the output might be
1942 You have: pound
1944 You want: grain
1945 * 6999.9999999999991
1946 / 0.00014285714285714287
1947 With the format '%.25g' you might get the following:
1949 You have: 1/3
1951 You want:
1952 Definition: 0.333333333333333314829616256247
1953 In this case the displayed value includes a series of digits that rep‐
1955 resent the underlying binary floating-point approximation to 1/3 but
1956 are not meaningful for the desired computation. In general, the result
1957 with excess precision is system dependent. The precision affects only
1958 the display of numbers; if a result relies on physical constants that
1959 are not known to the specified precision, the number of physically
1960 meaningful digits may be less than the number of digits shown.
1961 See the documentation for 'printf()' for more detailed descriptions of
1963 the format specification.
1964 The '--output-format' option is incompatible with the '--exponential'
1966 or '--digits' options; if the former is given in combination with
1967 either of the latter, the format is controlled by the last option
1968 given.
1969
1971 Some units have different values in different locations. The localiza‐
1972 tion feature accommodates this by allowing a units data file to specify
1973 definitions that depend on the user's locale.
1974 Locale
1976 A locale is a subset of a user's environment that indicates the user's
1977 language and country, and some attendant preferences, such as the for‐
1978 matting of dates. The 'units' program attempts to determine the locale
1979 from the POSIX setlocale function; if this cannot be done, 'units'
1980 examines the environment variables 'LC_CTYPE' and 'LANG'. On POSIX
1981 systems, a locale is of the form language'_'country, where language is
1982 the two-character code from ISO 639-1 and country is the two-character
1983 code from ISO 3166-1; language is lower case and country is upper case.
1984 For example, the POSIX locale for the United Kingdom is 'en_GB'.
1985 On systems running Microsoft Windows, the value returned by setlocale()
1987 is different from that on POSIX systems; 'units' attempts to map the
1988 Windows value to a POSIX value by means of a table in the file
1989 'locale_map.txt' in the same directory as the other data files. The
1990 file includes entries for many combinations of language and country,
1991 and can be extended to include other combinations. The
1992 'locale_map.txt' file comprises two tab-separated columns; each entry
1993 is of the form
1994 Windows-locale POSIX-locale
1996 where POSIX-locale is as described above, and Windows-locale typically
1998 spells out both the language and country. For example, the entry for
1999 the United States is
2000 English_United States en_US
2002 You can force 'units' to run in a desired locale by using the '-l'
2004 option.
2005 In order to create unit definitions for a particular locale you begin a
2007 block of definitions in a unit datafile with '!locale' followed by a
2008 locale name. The '!' must be the first character on the line. The
2009 'units' program reads the following definitions only if the current
2010 locale matches. You end the block of localized units with
2011 '!endlocale'. Here is an example, which defines the British gallon.
2012 !locale en_GB
2014 gallon 4.54609 liter
2015 !endlocale
2016 Additional Localization
2018 Sometimes the locale isn't sufficient to determine unit preferences.
2019 There could be regional preferences, or a company could have specific
2020 preferences. Though probably uncommon, such differences could arise
2021 with the choice of English customary units outside of English-speaking
2022 countries. To address this, 'units' allows specifying definitions that
2023 depend on environment variable settings. The environment variables can
2024 be controled based on the current locale, or the user can set them to
2025 force a particular group of definitions.
2026 A conditional block of definitions in a units data file begins with
2028 either '!var' or '!varnot' following by an environment variable name
2029 and then a space separated list of values. The leading '!' must
2030 appear in the first column of a units data file, and the conditional
2031 block is terminated by '!endvar'. Definitions in blocks beginning with
2032 '!var' are executed only if the environment variable is exactly equal
2033 to one of the listed values. Definitions in blocks beginning with
2034 '!varnot' are executed only if the environment variable does not equal
2035 any of the list values.
2036 The inch has long been a customary measure of length in many places.
2038 The word comes from the latin uncia meaning ``one twelfth,'' referring
2039 to its relationship with the foot. By the 20th century, the inch was
2040 officially defined in English-speaking countries relative to the yard,
2041 but until 1959, the yard differed slightly among those countries. In
2042 France the customary inch, which was displaced in 1799 by the meter,
2043 had a different length based on a french foot. These customary defini‐
2044 tions could be accommodated as follows:
2045 !var INCH_UNIT usa
2047 yard 3600|3937 m
2048 !endvar
2049 !var INCH_UNIT canada
2050 yard 0.9144 meter
2051 !endvar
2052 !var INCH_UNIT uk
2053 yard 0.91439841 meter
2054 !endvar
2055 !var INCH_UNIT canada uk usa
2056 foot 1|3 yard
2057 inch 1|12 foot
2058 !endvar
2059 !var INCH_UNIT france
2060 foot 144|443.296 m
2061 inch 1|12 foot
2062 line 1|12 inch
2063 !endvar
2064 !varnot INCH_UNIT usa uk france canada
2065 !message Unknown value for INCH_UNIT
2066 !endvar
2067 When 'units' reads the above definitions it will check the environment
2069 variable 'INCH_UNIT' and load only the definitions for the appropriate
2070 section. If 'INCH_UNIT' is unset or is not set to one of the four val‐
2071 ues listed then 'units' will run the last block. In this case that
2072 block uses the '!message' command to display a warning message. Alter‐
2073 natively that block could set default values.
2074 In order to create default values that are overridden by user settings
2076 the data file can use the '!set' command, which sets an environment
2077 variable only if it is not already set; these settings are only for
2078 the current 'units' invocation and do not persist. So if the example
2079 above were preceded by '!set INCH_UNIT france' then this would make
2080 'france' the default value for 'INCH_UNIT'. If the user had set the
2081 variable in the environment before invoking 'units', then 'units' would
2082 use the user's value.
2083 To link these settings to the user's locale you combine the '!set' com‐
2085 mand with the '!locale' command. If you wanted to combine the above
2086 example with suitable locales you could do by preceding the above defi‐
2087 nition with the following:
2088 !locale en_US
2090 !set INCH_UNIT usa
2091 !endlocale
2092 !locale en_GB
2093 !set INCH_UNIT uk
2094 !endlocale
2095 !locale en_CA
2096 !set INCH_UNIT canada
2097 !endlocale
2098 !locale fr_FR
2099 !set INCH_UNIT france
2100 !endlocale
2101 !set INCH_UNIT france
2102 These definitions set the overall default for 'INCH_UNIT' to 'france'
2104 and set default values for four locales appropriately. The overall
2105 default setting comes last so that it only applies when 'INCH_UNIT' was
2106 not set by one of the other commands or by the user.
2107 If the variable given after '!var' or '!varnot' is undefined then
2109 'units' prints an error message and ignores the definitions that fol‐
2110 low. Use '!set' to create defaults to prevent this situation from
2111 arising. The '-c' option only checks the definitions that are active
2112 for the current environment and locale, so when adding new definitions
2113 take care to check that all cases give rise to a well defined set of
2114 definitions.
2115
2117 The 'units' program uses the following environment variables:
2118 HOME Specifies the location of your home directory; it is used by
2120 'units' to find a personal units data file '.units'. On systems
2121 running Microsoft Windows, the file is 'unitdef.units', and if
2122 'HOME' does not exist, 'units' tries to determine your home
2123 directory from the 'HOMEDRIVE' and 'HOMEPATH' environment vari‐
2124 ables; if these variables do not exist, units finally tries
2125 'USERPROFILE'—typically 'C:\Users\username' (Windows Vista and
2126 Windows 7) or 'C:\Documents and Settings\username' (Windows XP).
2127 LC_CTYPE, LANG
2129 Checked to determine the locale if 'units' cannot obtain it from
2130 the operating system. Sections of the standard units data file
2131 are specific to certain locales.
2132 MYUNITSFILE
2134 Specifies your personal units data file. If this variable
2135 exists, 'units' uses its value rather than searching your home
2136 directory for '.units'. The personal units file will not be
2137 loaded if any data files are given using the '-f' option.
2138 PAGER Specifies the pager to use for help and for displaying the con‐
2140 formable units. The help function browses the units database
2141 and calls the pager using the '+n'n syntax for specifying a line
2142 number. The default pager is 'more'; 'PAGER' can be used to
2143 specify alternatives such as 'less', 'pg', 'emacs', or 'vi'.
2144 UNITS_ENGLISH
2146 Set to either 'US' or 'GB' to choose United States or British
2147 volume definitions, overriding the default from your locale.
2148 UNITSFILE
2150 Specifies the units data file to use (instead of the default).
2151 You can only specify a single units data file using this envi‐
2152 ronment variable. If units data files are given using the '-f'
2153 option, the file specified by 'UNITSFILE' will be not be loaded
2154 unless the '-f' option is given with the empty string
2155 ('units -f ""').
2156 UNITSLOCALEMAP
2158 Windows only; this variable has no effect on Unix-like systems.
2159 Specifies the units locale map file to use (instead of the
2160 default). This variable seldom needs to be set, but you can use
2161 it to ensure that the locale map file will be found if you spec‐
2162 ify a location for the units data file using either the '-f'
2163 option or the 'UNITSFILE' environment variable, and that loca‐
2164 tion does not also contain the locale map file.
2165
2167 The 'units' program uses two default data files: 'definitions.units'
2168 and 'currency.units'. The program can also use an optional personal
2169 units data file '.units' ('unitdef.units' under Windows) located in the
2170 user's home directory. The personal units data file is described in
2171 more detail in Units Data Files.
2172 On Unix-like systems, the data files are typically located in
2174 '/usr/share/units' if 'units' is provided with the operating system, or
2175 in '/usr/local/share/units' if 'units' is compiled from the source dis‐
2176 tribution. Note that the currency file 'currency.units' is a symbolic
2177 link to another location.
2178 On systems running Microsoft Windows, the files may be in the same
2180 locations if Unix-like commands are available, a Unix-like file struc‐
2181 ture is present (e.g., 'C:/usr/local'), and 'units' is compiled from
2182 the source distribution. If Unix-like commands are not available, a
2183 more common location is 'C:\Program Files (x86)\GNU\units' (for 64-bit
2184 Windows installations) or 'C:\Program Files\GNU\units' (for 32-bit
2185 installations).
2186 If 'units' is obtained from the GNU Win32 Project
2188 (http://gnuwin32.sourceforge.net/), the files are commonly in
2189 'C:\Program Files\GnuWin32\share\units'.
2190 If the default units data file is not an absolute pathname, 'units'
2192 will look for the file in the directory that contains the 'units' pro‐
2193 gram; if the file is not found there, 'units' will look in a directory
2194 '../share/units' relative to the directory with the 'units' program.
2195 You can determine the location of the files by running
2197 'units --version'. Running 'units --info' will give you additional
2198 information about the files, how 'units' will attempt to find them, and
2199 the status of the related environment variables.
2200
2202 The standard units data file is in Unicode, using UTF-8 encoding. Most
2203 definitions use only ASCII characters (i.e., code points U+0000 through
2204 U+007F); definitions using non-ASCII characters appear in blocks begin‐
2205 ning with '!utf8' and ending with '!endutf8'.
2206 When 'units' starts, it checks the locale to determine the character
2208 set. If 'units' is compiled with Unicode support and definitions; oth‐
2209 erwise these definitions are ignored. When Unicode support is active,
2210 'units' will check every line of all of the units data files for
2211 invalid or non-printing UTF-8 sequences; if such sequences occur,
2212 'units' ignores the entire line. In addition to checking validity,
2213 'units' determines the display width of non-ASCII characters to ensure
2214 proper positioning of the pointer in some error messages and to align
2215 columns for the 'search' and '?' commands.
2216 At present, 'units' does not support Unicode under Microsoft Windows.
2218 The UTF-16 and UTF-32 encodings are not supported on any systems.
2219 If definitions that contain non-ASCII characters are added to a units
2221 data file, those definitions should be enclosed within '!utf8' ...
2222 '!endutf8' to ensure that they are only loaded when Unicode support is
2223 available. As usual, the '!' must appear as the first character on
2224 the line. As discussed in Units Data Files, it's usually best to put
2225 such definitions in supplemental data files linked by an '!include'
2226 command or in a personal units data file.
2227 When Unicode support is not active, 'units' makes no assumptions about
2229 character encoding, except that characters in the range 00-7F hexadeci‐
2230 mal correspond to ASCII encoding. Non-ASCII characters are simply
2231 sequences of bytes, and have no special meanings; for definitions in
2232 supplementary units data files, you can use any encoding consistent
2233 with this assumption. For example, if you wish to use non-ASCII char‐
2234 acters in definitions when running 'units' under Windows, you can use a
2235 character set such as Windows ``ANSI'' (code page 1252 in the US and
2236 Western Europe). You can even use UTF-8, though some messages may be
2237 improperly aligned, and 'units' will not detect invalid UTF-8
2238 sequences. If you use UTF-8 encoding when Unicode support is not
2239 active, you should place any definitions with non-ASCII characters out‐
2240 side '!utf8' ... '!endutf8' blocks—otherwise, they will be ignored.
2241 Typeset material other than code examples usually uses the Unicode
2243 minus (U+2212) rather than the ASCII hyphen-minus operator (U+002D)
2244 used in 'units'; the figure dash (U+2012) and en dash (U+2013) are also
2245 occasionally used. To allow such material to be copied and pasted for
2246 interactive use or in units data files, 'units' converts these charac‐
2247 ters to U+002D before further processing. Because of this, none of
2248 these characters can appear in unit names.
2249
2251 If the 'readline' package has been compiled in, then when 'units' is
2252 used interactively, numerous command line editing features are avail‐
2253 able. To check if your version of 'units' includes 'readline', invoke
2254 the program with the '--version' option.
2255 For complete information about 'readline', consult the documentation
2257 for the 'readline' package. Without any configuration, 'units' will
2258 allow editing in the style of emacs. Of particular use with 'units'
2259 are the completion commands.
2260 If you type a few characters and then hit ESC followed by '?' then
2262 'units' will display a list of all the units that start with the char‐
2263 acters typed. For example, if you type 'metr' and then request comple‐
2264 tion, you will see something like this:
2265 You have: metr
2267 metre metriccup metrichorsepower metrictenth
2268 metretes metricfifth metricounce metricton
2269 metriccarat metricgrain metricquart metricyarncount
2270 You have: metr
2271 If there is a unique way to complete a unitname, you can hit the TAB
2273 key and 'units' will provide the rest of the unit name. If 'units'
2274 beeps, it means that there is no unique completion. Pressing the TAB
2275 key a second time will print the list of all completions.
2276 The readline library also keeps a history of the values you enter. You
2278 can move through this history using the up and down arrows. The his‐
2279 tory is saved to the file '.units_history' in your home directory so
2280 that it will persist across multiple 'units' invocations. If you wish
2281 to keep work for a certain project separate you can change the history
2282 filename using the '--history' option. You could, for example, make an
2283 alias for 'units' to 'units --history .units_history' so that 'units'
2284 would save separate history in the current directory. The length of
2285 each history file is limited to 5000 lines. Note also that if you run
2286 several concurrent copies of 'units' each one will save its new history
2287 to the history file upon exit.
2288
2290 The units program includes currency exchange rates and prices for some
2291 precious metals in the database. Of course, these values change over
2292 time, sometimes very rapidly, and 'units' cannot provide real time val‐
2293 ues. To update the exchange rates run the 'units_cur', which rewrites
2294 the file containing the currency rates, typically
2295 '/var/lib/units/currency.units' or
2296 'usr/local/com/units/currency.units'. This program requires 'python',
2297 and must be run with suitable permissions to write the file. To keep
2298 the rates updated automatically, run it using a cron job on a Unix-like
2299 system, or a similar scheduling program on a different system. Cur‐
2300 rency exchange rates are taken from Yahoo (http://finance.yahoo.com)
2301 and precious metals pricing from Packetizer (www.packetizer.com).
2302 These sites update once per day, so there is no benefit in running the
2303 update script more often than daily. You can run 'units_cur' with a
2304 filename specified on the command line and it will write the data to
2305 that file. If you give '-' for the file it will write to standard out‐
2306 put.
2307
2309 unit definition
2310 Define a regular unit.
2311 prefix- definition
2313 Define a prefix.
2314 funcname(var) noerror units=[in-units,out-units] domain=[x1,x2]
2316 range=[y1,y2] definition(var) ; inverse(funcname)
2317 Define a nonlinear unit or unit function. The four optional
2318 keywords 'noerror', 'units=', 'range=' and 'domain=' can appear
2319 in any order. The definition of the inverse is optional.
2320 tabname[out-units] noerror pair-list
2322 Define a piecewise linear unit. The pair list gives the points
2323 on the table listed in ascending order. The 'noerror' keyword
2324 is optional.
2325 !endlocale
2327 End a block of definitions beginning with '!locale'
2328 !endutf8
2330 End a block of definitions begun with '!utf8'
2331 !endvar
2333 End a block of definitions begun with '!var' or '!varnot'
2334 !include file
2336 Include the specified file.
2337 !locale value
2339 Load the following definitions only of the locale is set to
2340 value.
2341 !message text
2343 Display text when the database is read unless the quiet option
2344 ('-q') is enabled.
2345 !set variable value
2347 Sets the environment variable, variable, to the specified value
2348 only if it is not already set.
2349 !unitlist alias definition
2351 Define a unit list alias.
2352 !utf8 Load the following definitions only if 'units' is running with
2354 UTF-8 enabled.
2355 !var envar value-list
2357 Load the block of definitions that follows only if the environ‐
2358 ment variable envar is set to one of the values listed in the
2359 space-separated value list. If envar is not set, 'units' prints
2360 an error message and ignores the block of definitions.
2361 !varnot envar value-list
2363 Load the block of definitions that follows only if the environ‐
2364 ment variable envar is set to value that is not listed in the
2365 space-separated value list. If envar is not set, 'units' prints
2366 an error message and ignores the block of definitions.
2367
2370 /usr/share/units/definitions.units — the standard units data file
2371
2373 16 October 2017 UNITS(1)