jammy (3) putenv.3.gz

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 versions <= 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, or nonzero if an error occurs.  In the event of an error,
       errno is set to indicate the cause.

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)

COLOPHON

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