NAME¶
units - unit conversion program
OVERVIEW OF `UNITS'¶
The `units' program converts quantities expressed in various scales to their
equivalents in other scales. The `units' program can handle multiplicative
scale changes as well as nonlinear conversions such as Fahrenheit to Celsius.
Temperature conversions require a special syntax. See the examples below.
The units are defined in an external data file. You can use the extensive data
file that comes with this program, or you can provide your own data file to
suit your needs.
You can use the program interactively with prompts, or you can use it from the
command line.
INTERACTING WITH `UNITS'¶
To invoke units for interactive use, type `units' at your shell prompt. The
program will print something like this:
2131 units, 53 prefixes, 24 nonlinear units
You have:
At the `You have:' prompt, type the quantity and units that you are converting
from. For example, if you want to convert ten meters to feet, type `10
meters'. Next, `units' will print `You want:'. You should type the type of
units you want to convert
to. To convert to feet, you would type
`feet'. Note that if the readline library was compiled in then the tab key can
be used to complete unit names. See
Readline support, for more
information about readline.
The answer will be displayed in two ways. The first line of output, which is
marked with a `*' to indicate multiplication, gives the result of the
conversion you have asked for. The second line of output, which is marked with
a `/' to indicate division, gives the inverse of the conversion factor. If you
convert 10 meters to feet, `units' will print
* 32.808399
/ 0.03048
which tells you that 10 meters equals about 32.8 feet. The second number gives
the conversion in the opposite direction. In this case, it tells you that 1
foot is equal to about 0.03 dekameters since the dekameter is 10 meters. It
also tells you that 1/32.8 is about .03.
The `units' program prints the inverse because sometimes it is a more convenient
number. In the example above, for example, the inverse value is an exact
conversion: a foot is exactly .03048 dekameters. But the number given the
other direction is inexact.
If you try to convert grains to pounds, you will see the following:
You have: grains
You want: pounds
* 0.00014285714
/ 7000
From the second line of the output you can immediately see that a grain is equal
to a seven thousandth of a pound. This is not so obvious from the first line
of the output. If you find the output format confusing, try using the
`--verbose' option:
You have: grain
You want: aeginamina
grain = 0.00010416667 aeginamina
grain = (1 / 9600) aeginamina
If you request a conversion between units which measure reciprocal dimensions,
then `units' will display the conversion results with an extra note indicating
that reciprocal conversion has been done:
You have: 6 ohms
You want: siemens
reciprocal conversion
* 0.16666667
/ 6
Reciprocal conversion can be suppressed by using the `--strict' option. As
usual, use the `--verbose' option to get more comprehensible output:
You have: tex
You want: typp
reciprocal conversion
1 / tex = 496.05465 typp
1 / tex = (1 / 0.0020159069) typp
You have: 20 mph
You want: sec/mile
reciprocal conversion
1 / 20 mph = 180 sec/mile
1 / 20 mph = (1 / 0.0055555556) sec/mile
If you enter incompatible unit types, the `units' program will print a message
indicating that the units are not conformable and it will display the reduced
form for each unit:
You have: ergs/hour
You want: fathoms kg^2 / day
conformability error
2.7777778e-11 kg m^2 / sec^3
2.1166667e-05 kg^2 m / sec
If you only want to find the reduced form or definition of a unit, simply press
return at the `You want:' prompt. Here is an example:
You have: jansky
You want:
Definition: fluxunit = 1e-26 W/m^2 Hz = 1e-26 kg / s^2
The output from `units' indicates that the jansky is defined to be equal to a
fluxunit which in turn is defined to be a certain combination of watts,
meters, and hertz. The fully reduced (and in this case somewhat more cryptic)
form appears on the far right.
Some named units are treated as dimensionless in some situations. These include
the radian and steradian. These units will be treated as equal to 1 in units
conversions. Power is equal to torque times angular velocity. This conversion
can only be performed if the radian is dimensionless.
You have: (14 ft lbf) (12 radians/sec)
You want: watts
* 227.77742
/ 0.0043902509
Note that named dimensionaless units are not treated as dimensionless in other
contexts. They cannot be used as exponents so for example, `meter^radian' is
not allowed.
If you want a list of options you can type `?' at the `You want:' prompt. The
program will display a list of named units which are conformable with the unit
that you entered at the `You have:' prompt above. Note that conformable unit
combinations will not appear on this list.
Typing `help' at either prompt displays a short help message. You can also type
`help' followed by a unit name. This will invoke a pager on the units data
base at the point where that unit is defined. You can read the definition and
comments that may give more details or historical information about the unit.
Typing `search text' will display a list of all of the units whose names contain
`text' as a substring along with their definitions. This may help in the case
where you aren't sure of the right unit name.
USING `UNITS' NON-INTERACTIVELY¶
The `units' program can perform units conversions non-interactively from the
command line. To do this, type the command, type the original units
expression, and type the new units you want. You will probably need to protect
the units expressions from interpretation by the shell using single quote
characters.
If you type
units '2 liters' 'quarts'
then `units' will print
* 2.1133764
/ 0.47317647
and then exit. The output tells you that 2 liters is about 2.1 quarts, or
alternatively that a quart is about 0.47 times 2 liters.
If the conversion is successful, then `units' will return success (0) to the
calling environment. If `units' is given non-conformable units to convert, it
will print a message giving the reduced form of each unit and it will return
failure (nonzero) to the calling environment.
When `units' is invoked with only one argument, it will print out the definition
of the specified unit. It will return failure if the unit is not defined and
success if the unit is defined.
UNIT EXPRESSIONS¶
In order to enter more complicated units or fractions, you will need to use
operations such as powers, products and division. Powers of units can be
specified using the `^' character as shown in the following example, or by
simple concatenation: `cm3' is equivalent to `cm^3'. If the exponent is more
than one digit, the `^' is required. An exponent like `2^3^2' is evaluated
right to left. The `^' operator has the second highest precedence. The `**'
operator is provided as an alternative exponent operator.
You have: cm^3
You want: gallons
* 0.00026417205
/ 3785.4118
You have: arabicfoot * arabictradepound * force
You want: ft lbf
* 0.7296
/ 1.370614
Multiplication of units can be specified by using spaces, or an asterisk (`*').
If `units' is invoked with the `--product' option then the hyphen (`-') also
acts as a multiplication operator. Division of units is indicated by the slash
(`/') or by `per'.
You have: furlongs per fortnight
You want: m/s
* 0.00016630986
/ 6012.8727
Historically, multiplication in units was assigned a higher precedence than
division. This disagrees with the usual precedence rules which give
multiplication and division equal precedence, and it has been a source of
confusion for people who think of units as a calculator.
By default, multiplication using the star (`*') now has the same precedence as
division and hence follows the usual precedence rules. If units is invoked
with the the `--oldstar' option then then the old behavior is activated and
`*' will have the same precedence as the other multiplication operators
described next.
Multiplication using a space or using the hyphen has a higher precedence than
division and is evaluated left to right. So @samp{m/s s/day} is equivalent to
`m / s s day' and has dimensions of length per time cubed. Similarly, `1/2
meter' refers to a unit of reciprocal length equivalent to .5/meter, which is
probably not what you would intend if you entered that expression.
You can indicate division of numbers with the vertical dash (`|'), so if you
wanted half a meter you could write @samp{1|2 meter}. This operator has the
highest precedence so the square root of two thirds could be written
`2|3^1|2'.
You have: 1|2 inch
You want: cm
* 1.27
/ 0.78740157
Parentheses can be used for grouping as desired.
You have: (1/2) kg / (kg/meter)
You want: league
* 0.00010356166
/ 9656.0833
Prefixes are defined separately from base units. In order to get centimeters,
the units database defines `centi-' and `c-' as prefixes. Prefixes can appear
alone with no unit following them. An exponent applies only to the immediately
preceding unit and its prefix so that `cm^3' or `centimeter^3' refer to cubic
centimeters but `centi*meter^3' refers to hundredths of cubic meters. Only one
prefix is permitted per unit, so `micromicrofarad' will fail, but
`micro*microfarad' will work, as will `micro microfarad'..
For `units', numbers are just another kind of unit. They can appear as many
times as you like and in any order in a unit expression. For example, to find
the volume of a box which is 2 ft by 3 ft by 12 ft in steres, you could do the
following:
You have: 2 ft 3 ft 12 ft
You want: stere
* 2.038813
/ 0.49048148
You have: $ 5 / yard
You want: cents / inch
* 13.888889
/ 0.072
And the second example shows how the dollar sign in the units conversion can
precede the five. Be careful: `units' will interpret `$5' with no space as
equivalent to dollars^5.
Outside of the SI system, it is often desirable to add values of different units
together. You may also wish to use `units' as a calculator that keeps track of
units. Sums of conformable units are written with the `+' character.
You have: 2 hours + 23 minutes + 32 seconds
You want: seconds
* 8612
/ 0.00011611705
You have: 12 ft + 3 in
You want: cm
* 373.38
/ 0.0026782366
You have: 2 btu + 450 ft lbf
You want: btu
* 2.5782804
/ 0.38785542
The expressions which are added together must reduce to identical expressions in
primitive units, or an error message will be displayed:
You have: 12 printerspoint + 4 heredium
^
Illegal sum of non-conformable units
Historically `-' has been used for products of units, which complicates its
iterpretation in `units'. Because `units' provides several other ways to
obtain unit products, and because `-' is a subtraction operator in general
algebraic expressions, `units' treats the binary `-' as a subtraction operator
by default. This behavior can be altered using the `--product' option which
causes `units' to treat the binary `-' operator as a product operator. Note
that when `-' is a multiplication operator it has the same precedence as `*',
but when `-' is a subtraction operator it has the lower precedence as the
addition operator.
When `-' is used as a unary operator it negates its operand. Regardless of the
`units' options, if `-' appears after `(' or after `+' then it will act as a
negation operator. So you can always compute 20 degrees minus 12 minutes by
entering `20 degrees + -12 arcmin'. You must use this construction when you
define new units because you cannot know what options will be in force when
your definition is processed.
The `+' character sometimes appears in exponents like `3.43e+8'. This leads to
an ambiguity in an expression like `3e+2 yC'. The unit `e' is a small unit of
charge, so this can be regarded as equivalent to `(3e+2) yC' or `(3 e)+(2
yC)'. This ambiguity is resolved by always interpreting `+' as part of an
exponent if possible.
Several built in functions are provided: `sin', `cos', `tan', `ln', `log',
`log2', `exp', `acos', `atan' and `asin'. The `sin', `cos', and `tan'
functions require either a dimensionless argument or an argument with
dimensions of angle.
You have: sin(30 degrees)
You want:
Definition: 0.5
You have: sin(pi/2)
You want:
Definition: 1
You have: sin(3 kg)
^
Unit not dimensionless
The other functions on the list require dimensionless arguments. The inverse
trigonometric functions return arguments with dimensions of angle.
If you wish to take roots of units, you may use the `sqrt' or `cuberoot'
functions. These functions require that the argument have the appropriate
root. Higher roots can be obtained by using fractional exponents:
You have: sqrt(acre)
You want: feet
* 208.71074
/ 0.0047913202
You have: (400 W/m^2 / stefanboltzmann)^(1/4)
You have:
Definition: 289.80882 K
You have: cuberoot(hectare)
^
Unit not a root
Nonlinear units are represented using functional notation. They make possible
nonlinear unit conversions such temperature. This is different from the linear
units that convert temperature differences. Note the difference below. The
absolute temperature conversions are handled by units starting with `temp',
and you must use functional notation. The temperature differences are done
using units starting with `deg' and they do not require functional notation.
You have: tempF(45)
You want: tempC
7.2222222
You have: 45 degF
You want: degC
* 25
/ 0.04
Think of `tempF(x)' not as a function but as a notation which indicates that `x'
should have units of `tempF' attached to it. See
Nonlinear units. The
first conversion shows that if it's 45 degrees Fahrehneit outside it's 7.2
degrees Celsius. The second conversions indicates that a change of 45 degrees
Fahrenheit corresponds to a change of 25 degrees Celsius.
Some other examples of nonlinears units are ring size and wire gauge. There are
numerous different gauges and ring sizes. See the units database for more
details. Note that wire gauges with multiple zeroes are signified using
negative numbers where two zeroes is -1. Alternatively, you can use the
synonyms `g00', `g000', and so on that are defined in the units database.
You have: wiregauge(11)
You want: inches
* 0.090742002
/ 11.020255
You have: brwiregauge(g00)
You want: inches
* 0.348
/ 2.8735632
You have: 1 mm
You want: wiregauge
18.201919
INVOKING `UNITS'¶
You invoke `units' like this:
units [OPTIONS] [FROM-UNIT [TO-UNIT]]
If the FROM-UNIT and TO-UNIT are omitted, then the program will use interactive
prompts to determine which conversions to perform. See
Interactive use.
If both FROM-UNIT and TO-UNIT are given, `units' will print the result of that
single conversion and then exit. If only FROM-UNIT appears on the command
line, `units' will display the definition of that unit and exit. Units
specified on the command line will need to be quoted to protect them from
shell interpretation and to group them into two arguments. See
Command line
use.
The following options allow you to read in an alternative units file, check your
units file, or change the output format:
- -c, --check
- Check that all units and prefixes defined in the units data
file reduce to primitive units. Print a list of all units that cannot be
reduced. Also display some other diagnostics about suspicious definitions
in the units data file. Note that only definitions active in the current
locale are checked.
- --check-verbose
- Like the `-check' option, this option prints a list of
units that cannot be reduced. But to help find unit definitions that cause
endless loops, it lists the units as they are checked. If `units' hangs,
then the last unit to be printed has a bad definition. Note that only
definitions active in the current locale are checked.
- -o format, --output-format format
- Use the specified format for numeric output. Format is the
same as that for the printf function in the ANSI C standard. For example,
if you want more precision you might use `-o %.15g'.
- -f filename, --file filename
- Instruct `units' to load the units file `filename'. If
`filename' is the empty string (`-f "') then the default units file
will be loaded. This enables you to load the default file plus a personal
units file. Up to 25 units files may be specified on the command line.
This option overrides the `UNITSFILE' environment variable.
- -h, --help
- Print out a summary of the options for `units'.
- -m, --minus
- Causes `-' to be interpreted as a subtraction operator.
This is usually the default behavior.
- -p, --product
- Causes `-' to be interpreted as a multiplication operator
when it has two operands. It will act as a negation operator when it has
only one operand: `(-3)'. Note that by default `-' is treated as a
subtraction operator.
, --oldstar Causes `*' to have the old style precedence, higher than the
precedence of division so that `1/2*3' will equal `1/6'.
, --newstar Forces `*' to have the new (default) precedence which follows the
usual rules of algebra: the precedence of `*' is the same as the precedence of
`/', so that `1/2*3' will equal `3/2'.
, --compact Give compact output featuring only the conversion factor. This turns
off the `--verbose' option.
- -q, --quiet, --silent
- Suppress prompting of the user for units and the display of
statistics about the number of units loaded.
- -s, --strict
- Suppress conversion of units to their reciprocal units. For
example, `units' will normally convert hertz to seconds because these
units are reciprocals of each other. The strict option requires that units
be strictly conformable to perform a conversion, and will give an error if
you attempt to convert hertz to seconds.
- -1, --one-line
- Give only one line of output (the forward conversion). Do
not print the reverse conversion. Note that if a reciprocal conversion is
performed then `units' will still print the "reciprocal
conversion" line.
- -t, --terse
- Give terse output when converting units. This option can be
used when calling `units' from another program so that the output is easy
to parse. This option has the combined effect of these options: `--strict'
`--quiet' `--one-line' `--compact'.
- -v, --verbose
- Give slightly more verbose output when converting units.
When combined with the `-c' option this gives the same effect as
`--check-verbose'.
- -V, --version
- Print program version number, tell whether the readline
library has been included, and give the location of the default units data
file.
UNIT DEFINITIONS¶
The conversion information is read from a units data file which is called
`units.dat' and is probably located in the `/usr/local/share' directory. If
you invoke `units' with the `-V' option, it will print the location of this
file. The default file includes definitions for all familiar units,
abbreviations and metric prefixes. It also includes many obscure or archaic
units.
Many constants of nature are defined, including these:
pi |
ratio of circumference to diameter |
c |
speed of light |
e |
charge on an electron |
force |
acceleration of gravity |
mole |
Avogadro's number |
water |
pressure per unit height of water |
Hg |
pressure per unit height of mercury |
au |
astronomical unit |
k |
Boltzman's constant |
mu0 |
permeability of vacuum |
epsilon0 |
permitivity of vacuum |
G |
gravitational constant |
mach |
speed of sound |
The database includes atomic masses for all of the elements and numerous other
constants. Also included are the densities of various ingredients used in
baking so that `2 cups flour_sifted' can be converted to `grams'. This is not
an exhaustive list. Consult the units data file to see the complete list, or
to see the definitions that are used.
The unit `pound' is a unit of mass. To get force, multiply by the force
conversion unit `force' or use the shorthand `lbf'. (Note that `g' is already
taken as the standard abbreviation for the gram.) The unit `ounce' is also a
unit of mass. The fluid ounce is `fluidounce' or `floz'. British capacity
units that differ from their US counterparts, such as the British Imperial
gallon, are prefixed with `br'. Currency is prefixed with its country name:
`belgiumfranc', `britainpound'.
The US Survey foot, yard, and mile can be obtained by using the `US' prefix.
These units differ slightly from the international length units. They were in
general use until 1959, and are still used for geographic surveys. The acre is
officially defined in terms of the US Survey foot. If you want an acre defined
according to the international foot, use `intacre'. The difference between
these units is about 4 parts per million. The British also used a slightly
different length measure before 1959. These can be obtained with the prefix
`UK'.
When searching for a unit, if the specified string does not appear exactly as a
unit name, then the `units' program will try to remove a trailing `s' or a
trailing `es'. If that fails, `units' will check for a prefix. All of the
standard metric prefixes are defined.
To find out what units and prefixes are available, read the standard units data
file.
DEFINING NEW UNITS¶
All of the units and prefixes that `units' can convert are defined in the units
data file. If you want to add your own units, you can supply your own file.
You can also add your own units definitions in the `.units.dat' file in your
home directory. If this file exists it is read before the units data file. It
will not be read if any units files are specified on the command line.
A unit is specified on a single line by giving its name and an equivalence.
Comments start with a `#' character, which can appear anywhere in a line. The
backslash character (`´) acts as a continuation character if it appears
as the last character on a line, making it possible to spread definitions out
over several lines if desired. A file can be included by giving the command
`!include' followed by the file's name. The file will be sought in the same
directory as the parent file unless a full path is given.
Unit names must not contain any of the operator characters `+', `-', `*', `/',
`|', `^' or the parentheses. They cannot begin with a digit or a decimal point
(`.'), nor can they end with a digit (except for zero). Be careful to define
new units in terms of old ones so that a reduction leads to the primitive
units, which are marked with `!' characters. Dimensionless units are indicated
by using the string `!dimensionless' for the unit definition.
When adding new units, be sure to use the `-c' option to check that the new
units reduce properly. If you create a loop in the units definitions, then
`units' will hang when invoked with the `-c' options. You will need to use the
`--check-verbose' option which prints out each unit as it checks them. The
program will still hang, but the last unit printed will be the unit which
caused the infinite loop.
If you define any units which contain `+' characters, carefully check them
because the `-c' option will not catch non-conformable sums. Be careful with
the `-' operator as well. When used as a binary operator, the `-' character
can perform addition or multiplication depending on the options used to invoke
`units'. To ensure consistent behavior use `-' only as a unary negation
operator when writing units definitions. To multiply two units leave a space
or use the `*' operator with care, recalling that it has two possible
precedence values and may require parentheses to ensure consistent behavior.
To compute the difference of `foo' and `bar' write `foo+(-bar)' or even
`foo+-bar'.
Here is an example of a short units file that defines some basic units:
m |
! |
# The meter is a primitive unit |
sec |
! |
# The second is a primitive unit |
rad |
!dimensionless |
# The radian is dimensionless |
micro- |
1e-6 |
# Define a prefix |
minute |
60 sec |
# A minute is 60 seconds |
hour |
60 min |
# An hour is 60 minutes |
inch |
0.0254 m |
# Inch defined in terms of meters |
ft |
12 inches |
# The foot defined in terms of inches |
mile |
5280 ft |
# And the mile |
A unit which ends with a `-' character is a prefix. If a prefix definition
contains any `/' characters, be sure they are protected by parentheses. If you
define `half- 1/2' then `halfmeter' would be equivalent to `1 / 2
meter'.
DEFINING NONLINEAR UNITS¶
Some units conversions of interest are nonlinear; for example, temperature
conversions between the Fahrenheit and Celsius scales cannot be done by simply
multiplying by conversions factors.
When you give a linear unit definition such as `inch 2.54 cm' you are providing
information that `units' uses to convert values in inches into primitive units
of meters. For nonlinear units, you give a functional definition that provides
the same information.
Nonlinear units are represented using a functional notation. It is best to
regard this notation not as a function call but as a way of adding units to a
number, much the same way that writing a linear unit name after a number adds
units to that number. Internally, nonlinear units are defined by a pair of
functions which convert to and from linear units in the data file, so that an
eventual conversion to primitive units is possible.
Here is an example nonlinear unit definition:
tempF(x) [1;K] (x+(-32)) degF + stdtemp ; (tempF+(-stdtemp))/degF + 32
A nonlinear unit definition comprises a unit name, a dummy parameter name, two
functions, and two corresponding units. The functions tell `units' how to
convert to and from the new unit. In order to produce valid results, the
arguments of these functions need to have the correct dimensions. To
facilitate error checking, you may specify the dimensions.
The definition begins with the unit name followed immediately (with no spaces)
by a `(' character. In parentheses is the name of the parameter. Next is an
optional specification of the units required by the functions in this
definition. In the example above, the `tempF' function requires an input
argument conformable with `1'. For normal nonlinear units definitions the
forward function will always take a dimensionless argument. The inverse
function requires an input argument conformable with `K'. In general the
inverse function will need units that match the quantity measured by your
nonlinear unit. The sole purpose of the expression in brackets to enable
`units' to perform error checking on function arguments.
Next the function definitions appear. In the example above, the `tempF' function
is defined by
tempF(x) = (x+(-32)) degF + stdtemp
This gives a rule for converting `x' in the units `tempF' to linear units of
absolute temperature, which makes it possible to convert from tempF to other
units.
In order to make conversions to Fahrenheit possible, you must give a rule for
the inverse conversions. The inverse will be `x(tempF)' and its definition
appears after a `;' character. In our example, the inverse is
x(tempF) = (tempF+(-stdtemp))/degF + 32
This inverse definition takes an absolute temperature as its argument and
converts it to the Fahrenheit temperature. The inverse can be omitted by
leaving out the `;' character, but then conversions to the unit will be
impossible. If the inverse is omitted then the `--check' option will display a
warning. It is up to you to calculate and enter the correct inverse function
to obtain proper conversions. The `--check' option tests the inverse at one
point and print an error if it is not valid there, but this is not a guarantee
that your inverse is correct.
If you wish to make synonyms for nonlinear units, you still need to define both
the forward and inverse functions. Inverse functions can be obtained using the
`~' operator. So to create a synonym for `tempF' you could write
fahrenheit(x) [1;K] tempF(x); ~tempF(fahrenheit)
You may occasionally wish to define a function that operates on units. This can
be done using a nonlinear unit definition. For example, the definition below
provides conversion between radius and the area of a circle. Note that this
definition requires a length as input and produces an area as output, as
indicated by the specification in brackets.
circlearea(r) [m;m^2] pi r^2 ; sqrt(circlearea/pi)
Sometimes you may be interested in a piecewise linear unit such as many wire
gauges. Piecewise linear units can be defined by specifying conversions to
linear units on a list of points. Conversion at other points will be done by
linear interpolation. A partial definition of zinc gauge is
zincgauge[in] 1 0.002, 10 0.02, 15 0.04, 19 0.06, 23 0.1
In this example, `zincgauge' is the name of the piecewise linear unit. The
definition of such a unit is indicated by the embedded `[' character. After
the bracket, you should indicate the units to be attached to the numbers in
the table. No spaces can appear before the `]' character, so a definition like
`foo[kg meters]' is illegal; instead write `foo[kg*meters]'. The definition of
the unit consists of a list of pairs optionally separated by commas. This list
defines a function for converting from the piecewise linear unit to linear
units. The first item in each pair is the function argument; the second item
is the value of the function at that argument (in the units specified in
brackets). In this example, we define `zincgauge' at five points. For example,
we set `zincgauge(1)' equal to `0.002 in'. Definitions like this may be more
readable if written using continuation characters as
zincgauge[in] \
1 0.002 \
10 0.02 \
15 0.04 \
19 0.06 \
23 0.1
With the preceeding definition, the following conversion can be performed:
You have: zincgauge(10)
You want: in
* 0.02
/ 50
You have: .01 inch
You want: zincgauge
5
If you define a piecewise linear unit that is not strictly monotonic, then the
inverse will not be well defined. If the inverse is requested for such a unit,
`units' will return the smallest inverse. The `--check' option will print a
warning if a non-monotonic piecewise linear unit is encountered.
LOCALIZATION¶
Some units have different values in different locations. The localization
feature accomodates this by allowing the units database to specify region
dependent definitions. A locale region in the units database begins with
`!locale' followed by the name of the locale. The leading `!' must appear in
the first column of the units database. The locale region is terminated by
`!endlocale'. The following example shows how to define a couple units in a
locale.
!locale en_GB
ton brton
gallon brgallon
!endlocale
The current locale is specified by the `LOCALE' environment variable. Note that
the `-c' option only checks the definitions which are active for the current
locale.
ENVIRONMENT VARIABLES¶
The `units' programs uses the following environment variables.
- LOCALE
- Specifies the locale. The default is `en_US'. Sections of
the units database are specific to certain locales.
- PAGER
- Specifies the pager to use for help and for displaying the
conformable units. The help function browses the units database and calls
the pager using the `+nn' syntax for specifying a line number. The default
pager is `more', but `less', `emacs', or `vi' are possible
alternatives.
- UNITSFILE
- Specifies the units database file to use (instead of the
default). This will be overridden by the `-f' option. Note that you can
only specify a single units database using this environment variable.
READLINE SUPPORT¶
If the `readline' package has been compiled in, then when `units' is used
interactively, numerous command line editing features are available. To check
if your version of `units' includes the readline, invoke the program with the
`--version' option.
For complete information about readline, consult the documentation for the
readline package. Without any configuration, `units' will allow editing in the
style of emacs. Of particular use with `units' are the completion commands.
If you type a few characters and then hit `ESC' followed by the `?' key then
`units' will display a list of all the units which start with the characters
typed. For example, if you type `metr' and then request completion, you will
see something like this:
You have: metr
metre metriccup metrichorsepower metrictenth
metretes metricfifth metricounce metricton
metriccarat metricgrain metricquart metricyarncount
You have: metr
If there is a unique way to complete a unitname, you can hit the tab key and
`units' will provide the rest of the unit name. If `units' beeps, it means
that there is no unique completion. Pressing the tab key a second time will
print the list of all completions.
FILES¶
/usr/share/misc/units.dat - the standard units data file
AUTHOR¶
Adrian Mariano (adrian@cam.cornell.edu)