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─────Run-Time Library───────────────────────────────────────────────────────
 
     The getenv function searches the list of environment variables
     for an entry corresponding to <varname>.
 
     Environment variables define the environment in which a process
     executes. (For example, the LIB environment variable defines the
     default search path for libraries to be linked with a program.)
     Because the getenv function is case sensitive, the <varname>
     variable should match the case of the environment variable.
 
     Environment-table entries must not be changed directly. If an
     entry must be changed, use the _putenv function. To modify the
     returned value without affecting the environment table, use
     _strdup or strcpy to make a copy of the string.
 
     The getenv and _putenv functions use the global variable _environ
     to access the environment table. The _putenv function may change
     the value of _environ, thus invalidating the <envp> argument to
     the main function. Therefore, it is safer to use the _environ
     variable to access the environment table.
 
     Both the getenv and the _putenv functions operate only on the data
     structures accessible to the run-time library and not on the
     environment "segment" created for the process by the operating
     system.
 
     Return Value
 
     The getenv function returns a pointer to the environment-table
     entry containing the current string value of <varname>. The return
     value is NULL if the given variable is not currently defined.
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