Section (3) putenv
putenv — change or add an environment variable
putenv() function adds
or changes the value of environment variables. The argument
string is of the form
name does not already exist
in the environment, then
string is added to the
name does exist, then the
the environment is changed to
value. The string pointed to
part of the environment, so altering the string changes the
returns zero on success, or nonzero if an error occurs. In
the event of an error,
set to indicate the cause.
For an explanation of the terms used in this section, see attributes(7).
||Thread safety||MT-Unsafe const:env|
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
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
The 4.4BSD version, like glibc 2.0, uses a copy.
SUSv2 removes the
the prototype, and so does glibc 2.1.3.
The GNU C library implementation provides a nonstandard
does not include an equal sign:
then the named variable is removed from the caller_zsingle_quotesz_s environment.
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Copyright 1993 David Metcalfe (davidprism.demon.co.uk)
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Linux libc source code
Lewine_zsingle_quotesz_s _POSIX Programmer_zsingle_quotesz_s Guide_ (O_zsingle_quotesz_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 (faithcs.unc.edu)
Modified Fri Feb 14 21:47:50 1997 by Andries Brouwer (aebcwi.nl)
Modified Mon Oct 11 11:11:11 1999 by Andries Brouwer (aebcwi.nl)
Modified Wed Nov 10 00:02:26 1999 by Andries Brouwer (aebcwi.nl)
Modified Sun May 20 22:17:20 2001 by Andries Brouwer (aebcwi.nl)