A
symbol often referred to by the name "
period". It is also
often called the "
full stop", particularly in the
UK.
In most modern languages (including English) it is used as a separator, placed at the end of each sentence to signify the sentence is over. It is often also used after each letter within an acronym.
In North America and Australia, it is used as a separator to denote place value in a decimal-based fraction, i.e. 2.25 would be two and 25/100ths. In countries that follow SI strictly, such as those in South America or Europe, this is done with the comma, and the period is used as a separator for clarity placed every third digit, i.e. 10.000 for ten thousand. In America this is done with the comma. In perl, the period is used for decimal-fraction place value, and the underscore is used for arbitrary clarity divisions.
In many computing environments, the period is traditionally used as a separator between a file's name and its extension, the extension being used to denote file type. A file named index.html would be a file named index of type html.
In internet domain names, the period is used as a separator between TLD, domain, and any subdomains.
In C-like programming languages, the period is used as a separator to denote that the thing after the period is "inside" of the thing before the period; for example, thing1.thing2 would request an item (named thing2) inside of a specific variable (named thing1) which is a structure, class or union containing a variable (named thing2).
Perl also uses the period as a kind of string concatenation operator; (string1 . string2) would return a value equal to a string containing the contents of string1 followed by the contents of string2. It also uses . as a single-character-length wildcard in regular expressions.
In UNIX-like systems, any file with a name beginning with a . is viewed as being invisible. Also, each directory is traditionally viewed as containing an imaginary directory named ".", which is equivalent to the directory that contains the . directory. So if you need to give something a directory to operate on, and you want it to operate on the current directory, you give it the name of the . directory. Because the directory's name begins with a ., the directory is invisible. You mostly see it used when you are trying to run a program in the current directory-- most command-line shells require exact pathnames for programs not in in certain places, so to run a program in the current directory you have to give the shell an exact pathname by saying ./programtorun.See also ...
In SMTP, and thus most command-line mail clients (mailx, for example) a . alone on a line signifies the end of the e-mail.
The ASCII value of . is 46.