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.

1927

1927 (MCMXXVII) was a common year starting on Saturday (dominical letter B) of the Gregorian calendar and a common year starting on Friday (dominical letter C) of the Julian calendar, the 1927th year of the Common Era (CE) and Anno Domini (AD) designations, the 927th year of the 2nd millennium, the 27th year of the 20th century, and the 8th year of the 1920s decade. Note that the Julian day for 1927 is 13 calendar days difference, which continued to be used from 1582 until the complete conversion of the Gregorian calendar was entirely done in 1929.

Events

January

1500

Year 1500 (MD) was a leap year starting on Wednesday (link will display the full calendar) of the Julian calendar.

The year was seen as being especially important by many Christians in Europe, who thought it would bring the beginning of the end of the world. Their belief was based on the phrase "half-time after the time", when the apocalypse was due to occur, which appears in the Book of Revelation and was seen as referring to 1500.

Events

January–June

July–December