unsetenv(3p) [centos man page]

UNSETENV(3P)						     POSIX Programmer's Manual						      UNSETENV(3P)

PROLOG

       This  manual page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may differ (consult the correspond-
       ing Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.

NAME

       unsetenv - remove an environment variable

SYNOPSIS

       #include <stdlib.h>

       int unsetenv(const char *name);

DESCRIPTION

       The unsetenv() function shall remove an environment variable from the environment of the calling process. The name  argument  points  to  a
       string,	which is the name of the variable to be removed. The named argument shall not contain an '=' character. If the named variable does
       not exist in the current environment, the environment shall be unchanged and the function is considered to have completed successfully.

       If the application modifies environ or the pointers to which it points, the behavior of unsetenv() is undefined.  The  unsetenv()  function
       shall update the list of pointers to which environ points.

       The unsetenv() function need not be reentrant. A function that is not required to be reentrant is not required to be thread-safe.

RETURN VALUE

       Upon  successful  completion, zero shall be returned. Otherwise, -1 shall be returned, errno set to indicate the error, and the environment
       shall be unchanged.

ERRORS

       The unsetenv() function shall fail if:

       EINVAL The name argument is a null pointer, points to an empty string, or points to a string containing an '=' character.

       The following sections are informative.

EXAMPLES

       None.

APPLICATION USAGE

       None.

RATIONALE

       Refer to the RATIONALE section in setenv().

FUTURE DIRECTIONS

       None.

SEE ALSO

       getenv(), setenv(), the Base Definitions volume of IEEE Std 1003.1-2001, <stdlib.h>, <sys/types.h>, <unistd.h>

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technol-
       ogy -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
       Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and  the  original  IEEE
       and  The  Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained
       online at http://www.opengroup.org/unix/online.html .

IEEE
/The Open Group						       2003							      UNSETENV(3P)

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

PROLOG

       This  manual page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may differ (consult the correspond-
       ing Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.

NAME

       putenv - change or add a value to an environment

SYNOPSIS

       #include <stdlib.h>

       int putenv(char *string);

DESCRIPTION

       The putenv() function shall use the string argument to set environment variable values. The string argument should point to a string of the
       form  "	name= value ".	The putenv() function shall make the value of the environment variable name equal to value by altering an existing
       variable or creating a new one. In either case, the string pointed to by string shall become part  of  the  environment,  so  altering  the
       string shall change the environment. The space used by string is no longer used once a new string which defines name is passed to putenv().

       The putenv() function need not be reentrant. A function that is not required to be reentrant is not required to be thread-safe.

RETURN VALUE

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

ERRORS

       The putenv() function may fail if:

       ENOMEM Insufficient memory was available.

       The following sections are informative.

EXAMPLES

   Changing the Value of an Environment Variable
       The following example changes the value of the HOME environment variable to the value /usr/home.

	      #include <stdlib.h>
	      ...
	      static char *var = "HOME=/usr/home";
	      int ret;

	      ret = putenv(var);

APPLICATION USAGE

       The putenv() function manipulates the environment pointed to by environ, and can be used in conjunction with getenv().

       See exec(), for restrictions on changing the environment in multi-threaded applications.

       This routine may use malloc() to enlarge the environment.

       A  potential  error  is	to call putenv() with an automatic variable as the argument, then return from the calling function while string is
       still part of the environment.

       The setenv() function is preferred over this function.

RATIONALE

       The standard developers noted that putenv() is the only function available to add to the environment without permitting memory leaks.

FUTURE DIRECTIONS

       None.

SEE ALSO

       exec(), getenv(), malloc(), setenv(), the Base Definitions volume of IEEE Std 1003.1-2001, <stdlib.h>

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technol-
       ogy -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
       Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and  the  original  IEEE
       and  The  Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained
       online at http://www.opengroup.org/unix/online.html .

IEEE
/The Open Group						       2003								PUTENV(3P)