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  2007-07-26 "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 .B "int clearenv(void);"
  32 .fi
  33 .sp
  34 .in -4n
  35 Feature Test Macro Requirements for glibc (see
  36 .BR feature_test_macros (7)):
  37 .in
  38 .sp
  39 .BR clearenv ():
  40 _SVID_SOURCE || _XOPEN_SOURCE
  41 .SH DESCRIPTION
  42 The
  43 .BR clearenv ()
  44 function clears the environment of all name-value
  45 pairs and sets the value of the external variable
  46 .I environ
  47 to NULL.
  48 .SH "RETURN VALUE"
  49 The
  50 .BR clearenv ()
  51 function returns zero on success, and a non-zero
  52 value on failure.
  53 .\" Most versions of Unix return -1 on error, or do not even have errors.
  54 .\" Glibc info and the Watcom C library document "a non-zero value".
  55 .SH VERSIONS
  56 Not in libc4, libc5.
  57 In glibc since glibc 2.0.
  58 .SH "CONFORMING TO"
  59 Various Unix variants (DG/UX, HP-UX, QNX, ...).
  60 POSIX.9 (bindings for FORTRAN77).
  61 POSIX.1-1996 did not accept
  62 .BR clearenv ()
  63 and
  64 .BR putenv (3),
  65 but changed its mind and scheduled these functions for some
  66 later issue of this standard (cf. B.4.6.1).
  67 However, POSIX.1-2001
  68 only adds
  69 .BR putenv (3),
  70 and rejected
  71 .BR clearenv ().
  72 .SH NOTES
  73 Used in security-conscious applications.
  74 If it is unavailable
  75 the assignment
  76 .RS
  77 .nf
  78     environ = NULL;
  79 .fi
  80 .RE
  81 will probably do.
  82 .LP
  83 The DG/UX and Tru64 man pages write: If
  84 .I environ
  85 has been modified by anything other than the
  86 .BR putenv (3),
  87 .BR getenv (3),
  88 or
  89 .BR clearenv ()
  90 functions, then
  91 .BR clearenv ()
  92 will return an error and the process environment will remain unchanged.
  93 .\" .LP
  94 .\" HP-UX has a ENOMEM error return.
  95 .SH "SEE ALSO"
  96 .BR getenv (3),
  97 .BR putenv (3),
  98 .BR setenv (3),
  99 .BR unsetenv (3),
 100 .BR environ (7)