mirror of https://github.com/mkerrisk/man-pages
102 lines
3.2 KiB
Plaintext
102 lines
3.2 KiB
Plaintext
.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved
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.TH "PUTENV" P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
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.\" putenv
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.SH NAME
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putenv \- change or add a value to an environment
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.SH SYNOPSIS
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.LP
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\fB#include <stdlib.h>
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.br
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.sp
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int putenv(char *\fP\fIstring\fP\fB); \fP
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\fB
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.br
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\fP
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.SH DESCRIPTION
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.LP
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The \fIputenv\fP() function shall use the \fIstring\fP argument to
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set environment variable values. The \fIstring\fP argument
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should point to a string of the form " \fIname\fP= \fIvalue\fP ".
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The \fIputenv\fP() function shall make the value of the
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environment variable \fIname\fP equal to \fIvalue\fP by altering an
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existing variable or creating a new one. In either case, the
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string pointed to by \fIstring\fP shall become part of the environment,
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so altering the string shall change the environment. The
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space used by \fIstring\fP is no longer used once a new string which
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defines \fIname\fP is passed to \fIputenv\fP().
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.LP
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The \fIputenv\fP() function need not be reentrant. A function that
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is not required to be reentrant is not required to be
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thread-safe.
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.SH RETURN VALUE
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.LP
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Upon successful completion, \fIputenv\fP() shall return 0; otherwise,
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it shall return a non-zero value and set \fIerrno\fP to
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indicate the error.
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.SH ERRORS
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.LP
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The \fIputenv\fP() function may fail if:
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.TP 7
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.B ENOMEM
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Insufficient memory was available.
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.sp
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.LP
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\fIThe following sections are informative.\fP
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.SH EXAMPLES
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.SS Changing the Value of an Environment Variable
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.LP
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The following example changes the value of the \fIHOME\fP environment
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variable to the value \fB/usr/home\fP.
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.sp
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.RS
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.nf
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\fB#include <stdlib.h>
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\&...
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static char *var = "HOME=/usr/home";
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int ret;
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.sp
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ret = putenv(var);
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\fP
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.fi
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.RE
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.SH APPLICATION USAGE
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.LP
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The \fIputenv\fP() function manipulates the environment pointed to
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by \fIenviron\fP, and can be used in conjunction with \fIgetenv\fP().
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.LP
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See \fIexec\fP() , for restrictions on changing the environment in
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multi-threaded applications.
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.LP
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This routine may use \fImalloc\fP() to enlarge the environment.
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.LP
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A potential error is to call \fIputenv\fP() with an automatic variable
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as the argument, then return from the calling function
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while \fIstring\fP is still part of the environment.
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.LP
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The \fIsetenv\fP() function is preferred over this function.
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.SH RATIONALE
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.LP
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The standard developers noted that \fIputenv\fP() is the only function
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available to add to the environment without permitting
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memory leaks.
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.SH FUTURE DIRECTIONS
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.LP
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None.
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.SH SEE ALSO
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.LP
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\fIexec\fP() , \fIgetenv\fP() , \fImalloc\fP() , \fIsetenv\fP() ,
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the Base Definitions volume of
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IEEE\ Std\ 1003.1-2001, \fI<stdlib.h>\fP
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.SH COPYRIGHT
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Portions of this text are reprinted and reproduced in electronic form
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from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
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-- Portable Operating System Interface (POSIX), The Open Group Base
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Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
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Electrical and Electronics Engineers, Inc and The Open Group. In the
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event of any discrepancy between this version and the original IEEE and
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The Open Group Standard, the original IEEE and The Open Group Standard
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is the referee document. The original Standard can be obtained online at
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http://www.opengroup.org/unix/online.html .
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