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putenv(3) - putenv, putenv - change or add an environment variable - man 3 putenv

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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(3,n));

DESCRIPTION
       The  putenv()  function  adds or changes the value of environment vari-
       ables.  The argument string(3,n) is of the form name=value.   If  name  does
       not already exist in(1,8) the environment, then string(3,n) is added to the envi-
       ronment.  If name does exist, then the value of name in(1,8) the environment
       is  changed  to value.  The string(3,n) pointed to by string(3,n) becomes part of
       the environment, so altering the string(3,n) changes the environment.

RETURN VALUE
       The putenv() function returns zero  on  success,  or  -1  if(3,n)  an  error(8,n)
       occurs.

ERRORS
       ENOMEM Insufficient space to allocate new environment.

NOTES
       The  putenv()  function is not required to be reentrant, and the one in(1,8)
       libc4, libc5 and glibc2.0 is not, but the glibc2.1 version(1,3,5) is.

       Description for libc4, libc5, glibc: If the argument string(3,n) is  of  the
       form  name,  and  does  not contain an `=' character, then the variable
       name is removed from the environment.  If putenv() has  to  allocate  a
       new  array  environ,  and  the  previous  array  was  also allocated by
       putenv(), then it will be freed. In no case will the old storage  asso-
       ciated to the environment variable itself be freed.

       The  libc4  and  libc5  and  glibc 2.1.2 versions conform to SUSv2: the
       pointer string(3,n) given to putenv() is used.  In particular,  this  string(3,n)
       becomes  part  of  the  environment;  changing it later will change the
       environment.  (Thus, it is an error(8,n) is to call putenv() with  an  auto-
       matic  variable  as the argument, then return from the calling function
       while string(3,n)  is  still  part  of  the  environment.)   However,  glibc
       2.0-2.1.1  differs: a copy of the string(3,n) is used.  On the one hand this
       causes a memory leak, and on the other hand it violates SUSv2. This has
       been fixed in(1,8) glibc2.1.2.

       The BSD4.4 version(1,3,5), like glibc 2.0, uses a copy.

       SUSv2  removes the `const' from the prototype, and so does glibc 2.1.3.

CONFORMING TO
       SVID 3, POSIX, BSD 4.3

SEE ALSO
       clearenv(3), getenv(3), setenv(3), unsetenv(3), environ(5)



GNU                               1993-04-08                         PUTENV(3)

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