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Sanitize the environment by setting required variables to safe values and removing extraneous environment variables.  Set {{IFS}} to its default of "{{" \t\n"}}" (the first character is a space character). Set the {{PATH}} environment variable to the string returned by calling {{confstr()}} with the first argument {{\_CS_PATH}}.  Preserve the {{TZ}} environment variable (if present) which denotes the time zone (see the Open Group Base Specifications Issue 6 specifies for the  format for this variable \[[Open Group 04|AA. C References#Open Group 04]\]).

One way to clear the environment is to use the {{clearenv()}} function. The function {{clearenv()}} has an odd history; it was supposed to be defined in POSIX.1, but never made it into the standard. However, it is defined in POSIX.9 (the Fortran 77 bindings to POSIX), so there is a quasi-official status for it \[[Wheeler 03|AA. C References#Wheeler 03]\].