environment variable


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environment variable

(programming, operating system)
A variable that is bound in the current environment. When evaluating an expression in some environment, the evaluation of a variable consists of looking up its name in the environment and substituting its value.

Most programming languages have some concept of an environment but in Unix shell scripts it has a specific meaning slightly different from other contexts. In shell scripts, environment variables are one kind of shell variable. They differ from local variables and command line arguments in that they are inheritted by a child process. Examples are the PATH variable that tells the shell the file system paths to search to find command executables and the TZ variable which contains the local time zone. The variable called "SHELL" specifies the type of shell being used.

These variables are used by commands or shell scripts to discover things about the environment they are operating in. Environment variables can be changed or created by the user or a program.

To see a list of environment variables type "setenv" at the csh or tcsh prompt or "set" at the sh, bash, jsh or ksh prompt.

In other programming languages, e.g. functional programming languages, the environment is extended with new bindings when a function's parameters are bound to its actual arguments or when new variables are declared. In a block-structured procedural language, the environment usually consists of a linked list of activation records.

environment variable

An item of memory-resident data that provides a mechanism for users, applications and the operating system to interact with each other. Set up in memory by the operating system each time it is booted, the variables hold the current environment configuration, such as computer and login name, CPU type and the names of the system, application, home and temporary folders.

Command Line Assistance
A common environment variable is the Path, which holds any number of folder hierarchies that the OS can search when a program is run at the command line so that the full path to the executable does not have to be explicitly entered each time. See path environment variable and path.
References in periodicals archive ?
In these instances, models not adjusted for neighborhood median household income in associations of walkable built environment variables with BMI z-score are underadjusted, and neighborhood median household income is a qualitative confounder.
The hypothesis H4a suggests that the organizational characteristics variable moderates the relation between the environment and the technical innovation To obtain the results, a product of the environment variables (independent variable) and the organizational characteristics (proposed moderator variable) was defined, in order to represent the interaction between both variables.
Four cultural measures--uncertainty avoidance, power distance, future orientation, and performance orientation--were found to be positively and significantly related to the institutional environment variable.
Specific family environment variables related to communication patterns were investigated by Hammen (1991).
The magnitude of the coefficient on the legal environment variable drops from 2.
Three built environment variables were used in the analysis street connectivity, walk score, and ratio of fast-food/ full-service restaurants.
In this case, the easiest route is through Apache, which has permission - via mod_cgi - to set environment variables.
As for other macro environment variables such as [CASE.
Use and personalize windows environment variables to find data and files.
Panel C reports the interest rate environment variables.
With this objective we propose the hypothesis that dimensional and social status variables of individual trees reflect the effects of stand density, treatments, site index, and other growing environment variables.
Additionally, an included power calculator allows FPGA designers to analyze and optimize power requirements early in the design process block level by the changing of design environment variables.

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