units Version 1.52
units
The units program converts quantities expressed in various scales to
their equivalents in other scales. The units program can only handle
multiplicative scale changes. For example, it cannot convert Celsius to
Fahrenheit but it can convert temperature differences between those
temperature scales.
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.
unitsTo invoke units for interactive use, type units at your shell prompt. The program will print something like this:
1161 units, 53 prefixes
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.
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 output tells you that 10 meters equals about 32.8 feet. The second number gives the conversion in the reverse directions. 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 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.
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
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 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.
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.
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, a hyphen (`-') or an asterisk (`*'). Division of units is indicated by the slash (`/').
You have: furlongs/fortnight
You want: m/s
* 0.00016630986
/ 6012.8727
Multiplication has a higher precedence than division and is evaluated left to right, so `m/s * s/day' is equivalent to `m / s s day' and has dimensions of length per time cubed. In effect, the first `/' character marks the beginning of the denominator of your units. In particular, this means that writing `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. To indicate division of numbers, use the vertical dash (`|'). No spaces area permitted on either side of the vertical dash character.
You have: 1|2 inch
You want: cm
* 1.27
/ 0.78740157
An exponent applies only to the immediately preceeding 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.
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 preceed 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. 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:
12 printerspoint reduces to 0.0042175176 m
4 heredium reduces to 20145.828 m^2
Because `-' is used for products, it cannot also be used to form differences of units. If a `-' appears before numerical digits as the very first character on the input line or if it appears immediately after a `+' then the number will be evaluated as a negative number. So you can compute 20 degrees minus 12 minutes by entering `20 degrees+-12 arcmin'. The `+' character is sometimes used in exponents like `3.43e+8'. Exponents of this form cannot be used when forming sums of units, but they may be used otherwise.
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 section Interacting with units.
If the from-unit and to-unit are given, units will
print the result of that single conversion and then exit.
The 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 section Using units non-interactively.
The following options allow you to read in an alternative units file, check your units file, or change the output format:
units hangs, then the last unit to be printed has a bad
definition.
units.
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 use until 1959, but for geographic surveys, they are still used. 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 prefix and, if that
fails, it will try to remove a trailing `s' or a trailing `es'.
All of the standard metric prefixes are defined.
To find out what units are available, read the standard units data file.
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.
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.
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.
When adding new units, be sure to use the `-c' option to check that
the new units reduce properly. If you define any units which contain
`+' characters, carefully check them because the `-c' option
will not catch non-conformable sums.
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.
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 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 contains a `/' character, then when it is applied to a unit, that unit will be in the denominator. So the definition `half- 1/2' would give a `halfmeter' equal to `1 / 2 meter'. For this reason, the `/' character should be avoided in prefixes.
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.
units
This document was generated on 30 April 1997 using the texi2html translator version 1.51.