Length

In geometric measurements, length is the most extended dimension of an object. In the International System of Quantities, length is any quantity with dimension distance. In other contexts "length" is the measured dimension of an object. For example, it is possible to cut a length of a wire which is shorter than wire thickness.

Length may be distinguished from height, which is vertical extent, and width or breadth, which are the distance from side to side, measuring across the object at right angles to the length. Length is a measure of one dimension, whereas area is a measure of two dimensions (length squared) and volume is a measure of three dimensions (length cubed). In most systems of measurement, the unit of length is a base unit, from which other units are defined.

History

Measurement has been important ever since humans settled from nomadic lifestyles and started using building materials, occupying land and trading with neighbours. As society has become more technologically oriented, much higher accuracies of measurement are required in an increasingly diverse set of fields, from micro-electronics to interplanetary ranging.

Environment variable

Environment variables are a set of dynamic named values that can affect the way running processes will behave on a computer.

They are part of the environment in which a process runs. For example, a running process can query the value of the TEMP environment variable to discover a suitable location to store temporary files, or the HOME or USERPROFILE variable to find the directory structure owned by the user running the process.

They were introduced in their modern form in 1979 with Version 7 Unix, so are included in all Unix operating system flavors and variants from that point onward including Linux and OS X. From PC DOS 2.0 in 1982, all succeeding Microsoft operating systems including Microsoft Windows, and OS/2 also have included them as a feature, although with somewhat different syntax, usage and standard variable names.

Details

In all Unix and Unix-like systems, each process has its own separate set of environment variables. By default, when a process is created, it inherits a duplicate environment of its parent process, except for explicit changes made by the parent when it creates the child. At the API level, these changes must be done between running fork and exec. Alternatively, from command shells such as bash, a user can change environment variables for a particular command invocation by indirectly invoking it via env or using the ENVIRONMENT_VARIABLE=VALUE <command> notation. All Unix operating system flavors, DOS, and Windows have environment variables; however, they do not all use the same variable names. A running program can access the values of environment variables for configuration purposes.

Length (phonetics)

In phonetics, length or quantity is a feature of sounds that have distinctively extended duration compared with other sounds. There are long vowels as well as long consonants (the latter are often called geminates).

Many languages do not have distinctive length. Among the languages that have distinctive length, there are only a few that have both distinctive vowel length and distinctive consonant length. It is more common that there is only one or that they depend on each other.

The languages that distinguish between different lengths have usually long and short sounds. According to some linguists, Estonian and some Sami languages have three phonemic (meaning-distinguishing) lengths for consonants and vowels. Some Low German/Low Saxon varieties in the vicinity of Hamburg and some Moselle Franconian and Ripuiarian Franconian varieties do, too.

Strictly speaking, a pair of a long sound and a short sound should be identical except for their length. In certain languages, however, there are pairs of phonemes that are traditionally considered to be long-short pairs even though they differ not only in length, but also in quality, for instance English "long e" which is /iː/ (as in feet /fiːt/) vs. "short i" which is /ɪ/ (as in fit /fɪt/) or German "long e" which is /eː/ (as in Beet /beːt/ 'garden bed') vs. "short e" which is /ɛ/ (as in Bett /bɛt/ 'sleeping bed'). Also, tonal contour may reinforce the length, as in Estonian, where the over-long length is concomitant with a tonal variation resembling tonal stress marking.