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.TH rlm_expr 5 "5 February 2004" "" "FreeRADIUS Module"
.SH NAME
rlm_expr \- FreeRADIUS Module
.SH DESCRIPTION
The \fIrlm_expr\fP module allows the server to perform
limited mathematical calculations.  This module is not called
directly in any section, it is invoked through the dynamic expansion
of strings.
.PP
For example, some NAS boxes send a NAS-Port attribute
which is a 32-bit number composed of port, card, and interface, all in
different bytes.  To see these attributes split into pieces, you can
have an entry in the 'users' file like:

.DS
DEFAULT
.br
    Vendor-Interface = `%{expr: %{NAS-Port} / (256 * 256)}`,
.br
    Vendor-Card = `%{expr: (%{NAS-Port} / 256) %% 256}`,
.br
    Vendor-Port = `%{expr: %{NAS-Port} %% 256}`
.br

.DE
where the attributes Vendor-Interface, Vendor-Card, and Vendor-Port
are attributes created by either you or a vendor-supplied
dictionary.

The mathematical operators supported by the expression module are:
.TP
.B +
addition
.TP
.B -
subtraction
.TP
.B /
division
.TP
.B %%
modulo remainder
.TP
.B *
multiplication
.TP
.B &
boolean AND
.TP
.B |
boolean OR
.TP
.B ()
grouping of sub-expressions
.PP
NOTE: The modulo remainder operator is '%%', and not '%'.  This
is due to the '%' character being used as a special character for
dynamic translation.
.PP
NOTE: These operators do NOT have precedence.  The parsing
of the input string, and the calculation of the answer, is done
strictly left to right.  If you wish to order the expressions, you
MUST group them into sub-expression, as shown in the previous
example.
.PP
All of the calculations are performed as unsigned 32-bit integers.
.DE
.SH CONFIGURATION
.DS
modules {
  ...
.br
  expr {
.br
  }
.br
  ...
.br
}
.br
 ...
.br
instantiate {
  ...
.br
  expr
  ...
.br
}
.SH SECTIONS
.BR instantiate
.PP
.SH FILES
.I /etc/freeradius/3.0/radiusd.conf
.PP
.SH "SEE ALSO"
.BR radiusd (8),
.BR radiusd.conf (5)
.SH AUTHOR
Chris Parker, cparker@segv.org