On many platforms, the term “environment variable” has a natural meaning in terms of facilities provided by the operating system. This interpretation of the concept does not exclude other interpretations, such as a mapping to a set of configuration parameters in a database system.
Environment variable names are usually case sensitive. Names are usually of the form (letter|_) (letter|_|digit)*, but this varies by platform.Environment variable names are usually case sensitive. Names are usually of the form (letter|_) (letter|_|digit)*, but this varies by platform. The naming convention for built-in names such as =xpath-version= is chosen to avoid any conflict with names allowed by popular operating systems.Environment variable names are usually case sensitive. Names are usually of the form (letter|_) (letter|_|digit)*, but this varies by platform. The naming convention for built-in names such as =xpath-version= is chosen to avoid any conflict with names allowed by popular operating systems.
On some platforms, there may sometimes be multiple environment variables with the same name; in this case, it is implementation-dependent as to which is returned; see for example [POSIX.1-2008] (Chapter 8, Environment Variables). Implementations may use prefixes or other naming conventions to disambiguate the names.
The requirement to ensure that the function is deterministic means in practice that the implementation must make a snapshot of the environment variables at some time during execution, and return values obtained from this snapshot, rather than using live values that are subject to change at any time.
Operating system environment variables may be associated with a particular process, while queries and stylesheets may execute across multiple processes (or multiple machines). In such circumstances implementations may choose to provide access to the environment variables associated with the process in which the query or stylesheet processing was initiated.
In operating system shell languages, environment variables are often embellished with punctuation characters: for example $VARIABLE_NAME on Unix-based systems, or %VARIABLE_NAME% on Windows. The punctuation characters are not part of the name, and should not be present in the value of $name.
Security advice: UntrustedXP applications should not be permitted unrestricted access to environment variables. For example, the name of the account under which a query is running may be useful information to a would-be intruder. An implementation may therefore choose to restrict access to the environment, or may provide a facility to make fn:environment-variable always return the empty sequence.Security advice: Queries from untrusted sources should not be permitted unrestricted access to environment variables. For example, the name of the account under which the query is running may be useful information to a would-be intruder. An implementation may therefore choose to restrict access to the environment, or may provide a facility to make fn:environment-variable always return the empty sequence.Security advice: UntrustedXPQueries applicationsfrom untrusted sources should not be permitted unrestricted access to environment variables. For example, the name of the account under which athe query is running may be useful information to a would-be intruder. An implementation may therefore choose to restrict access to the environment, or may provide a facility to make fn:environment-variable always return the empty sequence.
This function overlaps with the capability offered by the system-property function in XSLT. It has been extended to provide information about the processor, primarily in order to offer a similar capability for non-XSLT environments.
The values returned for properties such as "=xpath-version=" may depend on how the processor has been configured.
The function fn:environment-variable has been available since XPath 3.0, and although the properties such as "=xpath-version=" are first defined in 4.0, an XPath 3.0 or 3.1 implementation that recognized these properties would be entirely conformant.