mirror of https://github.com/mkerrisk/man-pages
138 lines
4.5 KiB
Groff
138 lines
4.5 KiB
Groff
.\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
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.\"
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.\" %%%LICENSE_START(VERBATIM)
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.\" Permission is granted to make and distribute verbatim copies of this
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.\" manual provided the copyright notice and this permission notice are
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.\" preserved on all copies.
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.\"
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.\" Permission is granted to copy and distribute modified versions of this
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.\" manual under the conditions for verbatim copying, provided that the
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.\" entire resulting derived work is distributed under the terms of a
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.\" permission notice identical to this one.
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.\"
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.\" Since the Linux kernel and libraries are constantly changing, this
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.\" manual page may be incorrect or out-of-date. The author(s) assume no
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.\" responsibility for errors or omissions, or for damages resulting from
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.\" the use of the information contained herein. The author(s) may not
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.\" have taken the same level of care in the production of this manual,
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.\" which is licensed free of charge, as they might when working
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.\" professionally.
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.\"
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.\" Formatted or processed versions of this manual, if unaccompanied by
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.\" the source, must acknowledge the copyright and authors of this work.
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.\" %%%LICENSE_END
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.\"
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.\" References consulted:
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.\" Linux libc source code
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.\" Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
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.\" 386BSD man pages
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.\" Single UNIX Specification, Version 2
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.\" Modified Thu Apr 8 15:00:12 1993, David Metcalfe
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.\" Modified Sat Jul 24 18:44:45 1993, Rik Faith (faith@cs.unc.edu)
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.\" Modified Fri Feb 14 21:47:50 1997 by Andries Brouwer (aeb@cwi.nl)
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.\" Modified Mon Oct 11 11:11:11 1999 by Andries Brouwer (aeb@cwi.nl)
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.\" Modified Wed Nov 10 00:02:26 1999 by Andries Brouwer (aeb@cwi.nl)
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.\" Modified Sun May 20 22:17:20 2001 by Andries Brouwer (aeb@cwi.nl)
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.TH PUTENV 3 2015-08-08 "GNU" "Linux Programmer's Manual"
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.SH NAME
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putenv \- change or add an environment variable
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.SH SYNOPSIS
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.nf
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.B #include <stdlib.h>
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.sp
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.BI "int putenv(char *" string );
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.\" Not: const char *
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.fi
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.sp
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.in -4n
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Feature Test Macro Requirements for glibc (see
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.BR feature_test_macros (7)):
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.in
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.sp
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.BR putenv ():
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_XOPEN_SOURCE
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|| /* Glibc since 2.19: */ _DEFAULT_SOURCE
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|| /* Glibc versions <= 2.19: */ _SVID_SOURCE
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.SH DESCRIPTION
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The
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.BR putenv ()
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function adds or changes the value of environment
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variables.
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The argument \fIstring\fP is of the form \fIname\fP=\fIvalue\fP.
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If \fIname\fP does not already exist in the environment, then
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\fIstring\fP is added to the environment.
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If \fIname\fP does exist,
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then the value of \fIname\fP in the environment is changed to
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\fIvalue\fP.
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The string pointed to by \fIstring\fP becomes part of the environment,
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so altering the string changes the environment.
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.SH RETURN VALUE
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The
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.BR putenv ()
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function returns zero on success,
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or nonzero if an error occurs.
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In the event of an error,
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.I errno
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is set to indicate the cause.
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.SH ERRORS
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.TP
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.B ENOMEM
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Insufficient space to allocate new environment.
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.SH ATTRIBUTES
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For an explanation of the terms used in this section, see
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.BR attributes (7).
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.TS
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allbox;
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lb lb lb
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l l l.
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Interface Attribute Value
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T{
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.BR putenv ()
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T} Thread safety MT-Unsafe const:env
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.TE
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.SH CONFORMING TO
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POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD.
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.SH NOTES
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The
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.BR putenv ()
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function is not required to be reentrant, and the
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one in glibc 2.0 is not, but the glibc 2.1 version is.
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.\" .LP
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.\" Description for libc4, libc5, glibc:
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.\" If the argument \fIstring\fP is of the form \fIname\fP,
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.\" and does not contain an \(aq=\(aq character, then the variable \fIname\fP
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.\" is removed from the environment.
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.\" If
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.\" .BR putenv ()
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.\" has to allocate a new array \fIenviron\fP,
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.\" and the previous array was also allocated by
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.\" .BR putenv (),
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.\" then it will be freed.
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.\" In no case will the old storage associated
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.\" to the environment variable itself be freed.
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.LP
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Since version 2.1.2, the glibc implementation conforms to SUSv2:
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the pointer \fIstring\fP given to
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.BR putenv ()
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is used.
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In particular, this string becomes part of the environment;
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changing it later will change the environment.
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(Thus, it is an error is to call
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.BR putenv ()
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with an automatic variable
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as the argument, then return from the calling function while \fIstring\fP
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is still part of the environment.)
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However, glibc versions 2.0 to 2.1.1 differ: a copy of the string is used.
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On the one hand this causes a memory leak, and on the other hand
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it violates SUSv2.
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.LP
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The 4.4BSD version, like glibc 2.0, uses a copy.
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.LP
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SUSv2 removes the \fIconst\fP from the prototype, and so does glibc 2.1.3.
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.SH SEE ALSO
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.BR clearenv (3),
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.BR getenv (3),
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.BR setenv (3),
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.BR unsetenv (3),
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.BR environ (7)
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