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units
Convert units from one scale to another. 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.
SYNTAX
units OPTIONS [FROM-UNIT [TO-UNIT]]
OPTIONS
`-c'
`--check'
Check that all units and prefixes defined in the units file reduce
to primitive units. The program will print a list of all units
that cannot be reduced.
`--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.
`-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'
Use filename as the units data file rather than the default units
data file `units.dat'.
`-h'
`--help'
Print out a summary of the options for `units'.
`-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.
`-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.
To 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 tells you that 10 meters equals about 32.8 feet. The second number gives
the conversion in the reverse direction.
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.
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.
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 unit. 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
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.
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. 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.
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 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
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.
All of the units and prefixes that `units' can convert are defined
in the units data file.
To add your own units data file - see the man pages for the file layout.
"You have not converted a man because you have silenced him" - John Morley
Related commands:
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dc - Desk Calculator
factor - Print prime factors
wc - Print byte, word, and line counts