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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
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This page was generated on Wed Sep 19 20:14:39 BST 2007
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