man3/clearenv.3

   1 .\" Copyright 2001 John Levon <moz@compsoc.man.ac.uk>
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  23 .\" Additions, aeb, 2001-10-17.
  24 .TH CLEARENV 3  2001-10-17 "Linux" "Linux Programmer's Manual"
  25 .SH NAME
  26 clearenv \- clear the environment
  27 .SH SYNOPSIS
  28 .nf
  29 .B #include <stdlib.h>
  30 .sp
  31 .BI "int clearenv(void);"
  32 .fi
  33 .SH DESCRIPTION
  34 The
  35 .BR clearenv ()
  36 function clears the environment of all name-value
  37 pairs and sets the value of the external variable
  38 .I environ
  39 to NULL.
  40 .SH "RETURN VALUE"
  41 The
  42 .BR clearenv ()
  43 function returns zero on success, and a non-zero
  44 value on failure.
  45 .\" Most versions of Unix return -1 on error, or do not even have errors.
  46 .\" Glibc info and the Watcom C library document "a non-zero value".
  47 .SH VERSIONS
  48 Not in libc4, libc5.
  49 In glibc since glibc 2.0.
  50 .SH "CONFORMING TO"
  51 Various Unix variants (DG/UX, HP-UX, QNX, ...).
  52 POSIX.9 (bindings for FORTRAN77).
  53 POSIX.1-1996 did not accept
  54 .BR clearenv ()
  55 and
  56 .BR putenv (3),
  57 but changed its mind and scheduled these functions for some
  58 later issue of this standard (cf. B.4.6.1).
  59 However, POSIX.1-2001
  60 only adds
  61 .BR putenv (3),
  62 and rejected
  63 .BR clearenv ().
  64 .SH NOTES
  65 Used in security-conscious applications.
  66 If it is unavailable
  67 the assignment
  68 .RS
  69 .nf
  70     environ = NULL;
  71 .fi
  72 .RE
  73 will probably do.
  74 .LP
  75 The DG/UX and Tru64 man pages write: If
  76 .I environ
  77 has been modified by anything other than the
  78 .BR putenv (3),
  79 .BR getenv (3),
  80 or
  81 .BR clearenv ()
  82 functions, then
  83 .BR clearenv ()
  84 will return an error and the process environment will remain unchanged.
  85 .\" .LP
  86 .\" HP-UX has a ENOMEM error return.
  87 .SH "SEE ALSO"
  88 .BR getenv (3),
  89 .BR putenv (3),
  90 .BR setenv (3),
  91 .BR unsetenv (3),
  92 .BR environ (7)