.\" Copyright 2001 John Levon .\" .\" %%%LICENSE_START(VERBATIM) .\" Permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" Permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" .\" Since the Linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. The author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. The author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" Formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" %%%LICENSE_END .\" .\" Additions, aeb, 2001-10-17. .TH CLEARENV 3 2017-09-15 "Linux" "Linux Programmer's Manual" .SH NAME clearenv \- clear the environment .SH SYNOPSIS .nf .B #include .PP .B "int clearenv(void);" .fi .PP .RS -4 Feature Test Macro Requirements for glibc (see .BR feature_test_macros (7)): .RE .PP .BR clearenv (): /* Glibc since 2.19: */ _DEFAULT_SOURCE || /* Glibc versions <= 2.19: */ _SVID_SOURCE || _BSD_SOURCE .SH DESCRIPTION The .BR clearenv () function clears the environment of all name-value pairs and sets the value of the external variable .I environ to NULL. After this call, new variables can be added to the environment using .BR putenv (3) and .BR setenv (3). .SH RETURN VALUE The .BR clearenv () function returns zero on success, and a nonzero value on failure. .\" Most versions of UNIX return -1 on error, or do not even have errors. .\" Glibc info and the Watcom C library document "a nonzero value". .SH VERSIONS Available since glibc 2.0. .SH ATTRIBUTES For an explanation of the terms used in this section, see .BR attributes (7). .TS allbox; lb lb lb l l l. Interface Attribute Value T{ .BR clearenv () T} Thread safety MT-Unsafe const:env .TE .sp 1 .SH CONFORMING TO Various UNIX variants (DG/UX, HP-UX, QNX, ...). POSIX.9 (bindings for FORTRAN77). POSIX.1-1996 did not accept .BR clearenv () and .BR putenv (3), but changed its mind and scheduled these functions for some later issue of this standard (see \[sc]B.4.6.1). However, POSIX.1-2001 adds only .BR putenv (3), and rejected .BR clearenv (). .SH NOTES On systems where .BR clearenv () is unavailable, the assignment .PP .in +4n .EX environ = NULL; .EE .in .PP will probably do. .PP The .BR clearenv () function may be useful in security-conscious applications that want to precisely control the environment that is passed to programs executed using .BR exec (3). The application would do this by first clearing the environment and then adding select environment variables. .PP Note that the main effect of .BR clearenv () is to adjust the value of the pointer .BR environ (7); this function does not erase the contents of the buffers containing the environment definitions. .PP The DG/UX and Tru64 man pages write: If .I environ has been modified by anything other than the .BR putenv (3), .BR getenv (3), or .BR clearenv () functions, then .BR clearenv () will return an error and the process environment will remain unchanged. .\" .LP .\" HP-UX has a ENOMEM error return. .SH SEE ALSO .BR getenv (3), .BR putenv (3), .BR setenv (3), .BR unsetenv (3), .BR environ (7) .SH COLOPHON This page is part of release 5.10 of the Linux .I man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/.