| .\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk) |
| .\" |
| .\" %%%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| .\" manual page may be incorrect or out-of-date.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 |
| .\" |
| .\" References consulted: |
| .\" Linux libc source code |
| .\" Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991) |
| .\" 386BSD man pages |
| .\" Single UNIX Specification, Version 2 |
| .\" Modified Thu Apr 8 15:00:12 1993, David Metcalfe |
| .\" Modified Sat Jul 24 18:44:45 1993, Rik Faith (faith@cs.unc.edu) |
| .\" Modified Fri Feb 14 21:47:50 1997 by Andries Brouwer (aeb@cwi.nl) |
| .\" Modified Mon Oct 11 11:11:11 1999 by Andries Brouwer (aeb@cwi.nl) |
| .\" Modified Wed Nov 10 00:02:26 1999 by Andries Brouwer (aeb@cwi.nl) |
| .\" Modified Sun May 20 22:17:20 2001 by Andries Brouwer (aeb@cwi.nl) |
| .TH PUTENV 3 2019-03-06 "GNU" "Linux Programmer's Manual" |
| .SH NAME |
| putenv \- change or add an environment variable |
| .SH SYNOPSIS |
| .nf |
| .B #include <stdlib.h> |
| .PP |
| .BI "int putenv(char *" string ); |
| .\" Not: const char * |
| .fi |
| .PP |
| .in -4n |
| Feature Test Macro Requirements for glibc (see |
| .BR feature_test_macros (7)): |
| .in |
| .PP |
| .BR putenv (): |
| _XOPEN_SOURCE |
| || /* Glibc since 2.19: */ _DEFAULT_SOURCE |
| || /* Glibc versions <= 2.19: */ _SVID_SOURCE |
| .SH DESCRIPTION |
| The |
| .BR putenv () |
| function adds or changes the value of environment |
| variables. |
| The argument \fIstring\fP is of the form \fIname\fP=\fIvalue\fP. |
| If \fIname\fP does not already exist in the environment, then |
| \fIstring\fP is added to the environment. |
| If \fIname\fP does exist, |
| then the value of \fIname\fP in the environment is changed to |
| \fIvalue\fP. |
| The string pointed to by \fIstring\fP becomes part of the environment, |
| so altering the string changes the environment. |
| .SH RETURN VALUE |
| The |
| .BR putenv () |
| function returns zero on success, |
| or nonzero if an error occurs. |
| In the event of an error, |
| .I errno |
| is set to indicate the cause. |
| .SH ERRORS |
| .TP |
| .B ENOMEM |
| Insufficient space to allocate new environment. |
| .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 putenv () |
| T} Thread safety MT-Unsafe const:env |
| .TE |
| .SH CONFORMING TO |
| POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD. |
| .SH NOTES |
| The |
| .BR putenv () |
| function is not required to be reentrant, and the |
| one in glibc 2.0 is not, but the glibc 2.1 version is. |
| .\" .LP |
| .\" Description for libc4, libc5, glibc: |
| .\" If the argument \fIstring\fP is of the form \fIname\fP, |
| .\" and does not contain an \(aq=\(aq character, then the variable \fIname\fP |
| .\" is removed from the environment. |
| .\" If |
| .\" .BR putenv () |
| .\" has to allocate a new array \fIenviron\fP, |
| .\" and the previous array was also allocated by |
| .\" .BR putenv (), |
| .\" then it will be freed. |
| .\" In no case will the old storage associated |
| .\" to the environment variable itself be freed. |
| .PP |
| Since version 2.1.2, the glibc implementation conforms to SUSv2: |
| the pointer \fIstring\fP given to |
| .BR putenv () |
| is used. |
| In particular, this string becomes part of the environment; |
| changing it later will change the environment. |
| (Thus, it is an error to call |
| .BR putenv () |
| with an automatic variable |
| as the argument, then return from the calling function while \fIstring\fP |
| is still part of the environment.) |
| However, glibc versions 2.0 to 2.1.1 differ: a copy of the string is used. |
| On the one hand this causes a memory leak, and on the other hand |
| it violates SUSv2. |
| .PP |
| The 4.4BSD version, like glibc 2.0, uses a copy. |
| .PP |
| SUSv2 removes the \fIconst\fP from the prototype, and so does glibc 2.1.3. |
| .PP |
| The GNU C library implementation provides a nonstandard extension. |
| If |
| .I string |
| does not include an equal sign: |
| .PP |
| .in +4n |
| .EX |
| putenv("NAME"); |
| .EE |
| .in |
| .PP |
| then the named variable is removed from the caller's environment. |
| .SH SEE ALSO |
| .BR clearenv (3), |
| .BR getenv (3), |
| .BR setenv (3), |
| .BR unsetenv (3), |
| .BR environ (7) |