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GETENV(3)              FreeBSD Library Functions Manual              GETENV(3)

NAME
     getenv, putenv, setenv, unsetenv -- environment variable functions

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <stdlib.h>

     char *
     getenv(const char *name);

     int
     setenv(const char *name, const char *value, int overwrite);

     int
     putenv(const char *string);

     void
     unsetenv(const char *name);

DESCRIPTION
     These functions set, unset and fetch environment variables from the host
     environment list.  For compatibility with differing environment conven-
     tions, the given arguments name and value may be appended and prepended,
     respectively, with an equal sign ``=''.

     The getenv() function obtains the current value of the environment vari-
     able, name.  The application should not modify the string pointed to by
     the getenv() function.

     The setenv() function inserts or resets the environment variable name in
     the current environment list.  If the variable name does not exist in the
     list, it is inserted with the given value.  If the variable does exist,
     the argument overwrite is tested; if overwrite is zero, the variable is
     not reset, otherwise it is reset to the given value.

     The putenv() function takes an argument of the form ``name=value'' and is
     equivalent to:

           setenv(name, value, 1);

     The unsetenv() function deletes all instances of the variable name
     pointed to by name from the list.

RETURN VALUES
     The getenv() function returns the value of the environment variable as a
     NUL-terminated string.  If the variable name is not in the current envi-
     ronment, NULL is returned.

     The setenv() and putenv() functions return the value 0 if successful;
     otherwise the value -1 is returned and the global variable errno is set
     to indicate the error.

ERRORS
     [ENOMEM]           The function setenv() or putenv() failed because they
                        were unable to allocate memory for the environment.

SEE ALSO
     csh(1), sh(1), execve(2), environ(7)

STANDARDS
     The getenv() function conforms to ISO/IEC 9899:1990 (``ISO C90'').

HISTORY
     The functions setenv() and unsetenv() appeared in Version 7 AT&T UNIX.
     The putenv() function appeared in 4.3BSD-Reno.

BUGS
     Successive calls to setenv() or putenv() assigning a differently sized
     value to the same name will result in a memory leak.  The FreeBSD seman-
     tics for these functions (namely, that the contents of value are copied
     and that old values remain accessible indefinitely) make this bug
     unavoidable.  Future versions may eliminate one or both of these semantic
     guarantees in order to fix the bug.

FreeBSD 6.2                    October 12, 2006                    FreeBSD 6.2

NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUES | ERRORS | SEE ALSO | STANDARDS | HISTORY | BUGS

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