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PUTENV(3) Linux Programmer's Manual PUTENV(3)
NAME
putenv - change or add an environment variable
SYNOPSIS
#include <stdlib.h>
int putenv(char *string);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
putenv():
_XOPEN_SOURCE
|| /* Glibc since 2.19: */ _DEFAULT_SOURCE
|| /* Glibc <= 2.19: */ _SVID_SOURCE
DESCRIPTION
The putenv() function adds or changes the value of environment variables. The argument string is of the form name=value. If name does not already exist in the
environment, then string is added to the environment. If name does exist, then the value of name in the environment is changed to value. The string pointed to
by string becomes part of the environment, so altering the string changes the environment.
RETURN VALUE
The putenv() function returns zero on success. On failure, it returns a nonzero value, and errno is set to indicate the error.
ERRORS
ENOMEM Insufficient space to allocate new environment.
ATTRIBUTES
For an explanation of the terms used in this section, see attributes(7).
┌──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┬───────────────┬─────────────────────┐
│Interface │ Attribute │ Value │
├──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┼───────────────┼─────────────────────┤
│putenv() │ Thread safety │ MT-Unsafe const:env │
└──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┴───────────────┴─────────────────────┘
CONFORMING TO
POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD.
NOTES
The putenv() function is not required to be reentrant, and the one in glibc 2.0 is not, but the glibc 2.1 version is.
Since version 2.1.2, the glibc implementation conforms to SUSv2: the pointer string given to 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 putenv() with an automatic variable as the argument, then return from
the calling function while string 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.
The 4.4BSD version, like glibc 2.0, uses a copy.
SUSv2 removes the const from the prototype, and so does glibc 2.1.3.
The GNU C library implementation provides a nonstandard extension. If string does not include an equal sign:
putenv("NAME");
then the named variable is removed from the caller's environment.
SEE ALSO
clearenv(3), getenv(3), setenv(3), unsetenv(3), environ(7)
GNU 2021-03-22 PUTENV(3)