该变量用于说明在脚本中如何处理，所需环境变量的验证必须在脚本执行前定义。
This variable is used to illustrate how to handle in the script, the verification that required environment variables must be defined prior to running the script.
程序的man页面中通常包含对自定义应用程序环境变量的说明。
Custom application environment variables are typically documented in the program's man pages.
事实上，它只是说明变量定义在程序的其他地方。
In effect, it claims that a definition of the variable exists elsewhere in the program.
说明：在REXX未定义的主机变量。
说明：在REXX未定义的主机变量。
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