1PUTENV(3P)                 POSIX Programmer's Manual                PUTENV(3P)
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PROLOG

6       This  manual  page is part of the POSIX Programmer's Manual.  The Linux
7       implementation of this interface may differ (consult the  corresponding
8       Linux  manual page for details of Linux behavior), or the interface may
9       not be implemented on Linux.
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NAME

12       putenv - change or add a value to an environment
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SYNOPSIS

15       #include <stdlib.h>
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17       int putenv(char *string);
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DESCRIPTION

21       The putenv() function shall use the string argument to set  environment
22       variable  values.  The  string argument should point to a string of the
23       form " name= value ".  The putenv() function shall make  the  value  of
24       the  environment  variable  name equal to value by altering an existing
25       variable or creating a new one. In either case, the string  pointed  to
26       by  string shall become part of the environment, so altering the string
27       shall change the environment. The space used by  string  is  no  longer
28       used once a new string which defines name is passed to putenv().
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30       The  putenv()  function  need  not be reentrant. A function that is not
31       required to be reentrant is not required to be thread-safe.
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RETURN VALUE

34       Upon successful completion, putenv()  shall  return  0;  otherwise,  it
35       shall return a non-zero value and set errno to indicate the error.
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ERRORS

38       The putenv() function may fail if:
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40       ENOMEM Insufficient memory was available.
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43       The following sections are informative.
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EXAMPLES

46   Changing the Value of an Environment Variable
47       The  following  example changes the value of the HOME environment vari‐
48       able to the value /usr/home.
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51              #include <stdlib.h>
52              ...
53              static char *var = "HOME=/usr/home";
54              int ret;
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57              ret = putenv(var);
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APPLICATION USAGE

60       The putenv() function manipulates the environment pointed to  by  envi‐
61       ron, and can be used in conjunction with getenv().
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63       See  exec(),  for  restrictions  on  changing the environment in multi-
64       threaded applications.
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66       This routine may use malloc() to enlarge the environment.
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68       A potential error is to call putenv() with an automatic variable as the
69       argument,  then  return from the calling function while string is still
70       part of the environment.
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72       The setenv() function is preferred over this function.
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RATIONALE

75       The standard developers noted that putenv() is the only function avail‐
76       able to add to the environment without permitting memory leaks.
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FUTURE DIRECTIONS

79       None.
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SEE ALSO

82       exec(),  getenv(),  malloc(),  setenv(), the Base Definitions volume of
83       IEEE Std 1003.1-2001, <stdlib.h>
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86       Portions of this text are reprinted and reproduced in  electronic  form
87       from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
88       -- Portable Operating System Interface (POSIX),  The  Open  Group  Base
89       Specifications  Issue  6,  Copyright  (C) 2001-2003 by the Institute of
90       Electrical and Electronics Engineers, Inc and The Open  Group.  In  the
91       event of any discrepancy between this version and the original IEEE and
92       The Open Group Standard, the original IEEE and The Open Group  Standard
93       is  the  referee document. The original Standard can be obtained online
94       at http://www.opengroup.org/unix/online.html .
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98IEEE/The Open Group                  2003                           PUTENV(3P)
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