UNITS(1) FreeBSD General Commands Manual UNITS(1)
NAME
units - conversion calculator
SYNOPSIS
units [-ehqtUVv] [-f unitsfile] [-o format] [from to]
DESCRIPTION
The units program converts quantities expressed in various scales to
their equivalents in other scales. It can only handle multiplicative or
affine scale changes.
units can work interactively by prompting the user for input (see
EXAMPLES) or non-interactively, providing a conversion for given
arguments from and to.
The following options are available:
-e, --exponential
Same as -o %6e (see the description of the -o flag).
-f unitsfile, --file unitsfile
Specify the name of the units data file to load. This option
may be specified multiple times.
-H historyfile, --history historyfile
Ignored, for compatibility with GNU units.
-h, --help
Show an overview of options.
-o format, --output-format format
Select the output format string by which numbers are printed.
Defaults to "%.8g".
-q, --quiet
Suppress prompting of the user for units and the display of
statistics about the number of units loaded.
-t, --terse
Only print the result. This is used when calling units from
other programs for easy to parse results.
-U, --unitsfile
Print the location of the default unit file if it exists.
Otherwise, print "Units data file not found".
-V, --version
Print the version number (which is fixed at "FreeBSD units"),
the path to the units data file and exit.
-v, --verbose
Print the units in the conversion output. Be more verbose in
general.
from to Allow a single unit conversion to be done directly from the
command line. The program will not print prompts. It will
print out the result of the single specified conversion. Both
arguments, i.e., from and to, can be just a unit (e.g., "cm"), a
quantity (e.g., "42"), or a quantity with a unit (e.g., "42 cm")
Mathematical operators
- Powers of units can be specified using the "^" character as shown in
the example, or by simple concatenation: "cm3" is equivalent to
"cm^3". See the BUGS section for details on the limitations of
exponent values.
- Multiplication of units can be specified by using spaces (" "), a
dash ("-") or an asterisk ("*").
- Division of units is indicated by the slash ("/").
- Division of numbers must be indicated using the vertical bar ("|").
Note that multiplication has a higher precedence than division, so
"m/s/s" is the same as "m/s^2" or "m/s s".
Units
The conversion information is read from a units data file. The default
file includes definitions for most familiar units, abbreviations and
metric prefixes. Some constants of nature included are:
pi ratio of circumference to diameter
c speed of light
e charge on an electron
g acceleration of gravity
force same as g
mole Avogadro's number
water pressure per unit height of water
mercury pressure per unit height of mercury
au astronomical unit
The unit "pound" is a unit of mass. Compound names are run together so
"pound force" is a unit of force. The unit "ounce" is also a unit of
mass. The fluid ounce is "floz". British units that differ from their
US counterparts are prefixed with "br", and currency is prefixed with its
country name: "belgiumfranc", "britainpound". When searching for a unit,
if the specified string does not appear exactly as a unit name, then
units will try to remove a trailing "s" or a trailing "es" and check
again for a match.
Units file format
To find out what units are available read the standard units 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. 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. The
units program will not detect infinite loops that could be caused by
careless unit definitions. Comments in the unit definition file begin
with a "#" or "/" character at the beginning of a line.
Prefixes are defined in the same way as standard units, but with a
trailing dash ("-") at the end of the prefix name. If a unit is not
found even after removing trailing "s" or "es", then it will be checked
against the list of prefixes. Prefixes will be removed until a legal
base unit is identified.
ENVIRONMENT
PATH The colon-separated list of root directories at which units tries
to find /usr/share/misc/definitions.units.
For example if PATH is set to "/tmp:/:/usr/local", no -f flags are
provided, and /usr/share/misc/definitions.units is missing then
units tries to open the following files as the default units file:
/tmp/usr/share/misc/definitions.units,
/usr/share/misc/definitions.units, and
/usr/local/usr/share/misc/definitions.units.
FILES
/usr/share/misc/definitions.units The standard units file.
EXIT STATUS
The units utility exits 0 on success, and >0 if an error occurs.
EXAMPLES
Example 1: Simple conversion of units
This example shows how to do simple conversions, for example from
gigabytes to bytes:
$ units -o %0.f -t '4 gigabytes' bytes
4294967296
The -o %0.f part of the command is required to print the result in a
non-scientific notation (e.g, 4294967296 instead of 4.29497e+09).
Example 2: Interactive usage
Here is an example of an interactive session where the user is prompted
for units:
You have: meters
You want: feet
* 3.2808399
/ 0.3048
You have: cm^3
You want: gallons
* 0.00026417205
/ 3785.4118
You have: meters/s
You want: furlongs/fortnight
* 6012.8848
/ 0.00016630952
You have: 1|2 inch
You want: cm
* 1.27
/ 0.78740157
You have: 85 degF
You want: degC
29.444444
Example 3: Difference between "|" and "/" division
The following command shows how to convert half a meter to centimeters.
$ units '1|2 meter' cm
* 50
/ 0.02
units prints the expected result because the division operator for
numbers ("|") was used.
Using the division operator for units ("/") would result in an error:
$ units '1/2 meter' cm
conformability error
0.5 / m
0.01 m
It is because units interprets "1/2 meter" as "0.5/meter", which is not
conformable to "cm".
Example 4: Simple units file
Here is an example of a short units file that defines some basic units:
m !a!
sec !b!
micro- 1e-6
minute 60 sec
hour 60 min
inch 0.0254 m
ft 12 inches
mile 5280 ft
Example 5: Viewing units and conversions of the default units file
The following shell one-liner allows the user to view the contents of
the default units file:
$ less "$(units -U)"
DIAGNOSTICS
can't find units file '%s' The default units file is not in its default
location (see FILES) and it is not present in any file tree starting with
their roots at directories from PATH (see ENVIRONMENT).
cap_rights_limit() failed See capsicum(4).
conformability error It is not possible to reduce the given units to one
common unit: they are not conformable. Instead of a conversion, units
will display the reduced form for each provided 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
Could not initialize history See editline(3).
dupstr strdup(3) failed.
memory for prefixes exceeded in line %d Over 100 prefixes were defined.
memory for units exceeded in line %d Over 1000 prefixes were defined.
memory overflow in unit reduction The requested conversion involves too
many units (see BUGS).
redefinition of prefix '%s' on line %d ignored
redefinition of unit '%s' on line %d ignored
unexpected end of prefix on line %d
unexpected end of unit on line %d
Units data file not found The default units file is missing.
unable to enter capability mode See capsicum(4).
unable to open units file '%s' One of the user-specified units files
cannot be opened.
unit reduces to zero
unknown unit '%s' The provided unit cannot be found in the units file.
WARNING: conversion of non-proportional quantities. units may fail to
convert from to to because the units are not proportional. The warning
is printed when a quantity is a part of the to argument. It can be
illustrated on an example of conversion from Fahrenheit to Celsius:
$ units "degF" "degC"
(-> x*0.55555556g -17.777778g)
(<- y*1.8g 32g)
$ units "degF" "1 degC"
WARNING: conversion of non-proportional quantities.
(-> x*0.55555556g -17.777778g)
(<- y*1.8g 32g)
$ units "1 degF" "1 degC"
WARNING: conversion of non-proportional quantities.
-17.222222
SEE ALSO
bc(1)
HISTORY
The units first appeared in NetBSD and was ported to FreeBSD 2.2.0.
The manual page was significantly rewritten in FreeBSD 13.0 by Mateusz
Piotrowski <0mp@FreeBSD.org>.
AUTHORS
Adrian Mariano <adrian@cam.cornell.edu>
BUGS
The effect of including a "/" in a prefix is surprising.
Exponents entered by the user can be only one digit. You can work around
this by multiplying several terms.
The user must use "|" to indicate division of numbers and "/" to indicate
division of symbols. This distinction should not be necessary.
The program contains various arbitrary limits on the length of the units
converted and on the length of the data file.
The program should use a hash table to store units so that it does not
take so long to load the units list and check for duplication.
It is not possible to convert a negative value.
The units program does not handle reductions of long lists of units very
well:
$ units "$(yes m | head -n 154)" "$(yes cm | head -n 154)"
* 1e+308
/ 1e-308
$ units "$(yes m | head -n 333)" "$(yes cm | head -n 333)"
* inf
/ 0
$ units "$(yes m | head -n 500)" "$(yes cm | head -n 500)"
units: memory overflow in unit reduction
conformability error
1 m^500
1 centi cm^499
$ units "$(yes m | head -n 501)" "$(yes cm | head -n 501)"
units: memory overflow in unit reduction
units: memory overflow in unit reduction
units: memory overflow in unit reduction
conformability error
1 m^500
1 centi cm^499
FreeBSD 13.1-RELEASE-p6 March 17, 2020 FreeBSD 13.1-RELEASE-p6
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