[Freeswitch-users] variable not being replaced in dialplan

[Juan Pablo L.]

Good morning, i have the following entry in my dialplan to dialout
using a gateway:

<extension name="gw_outbound_call">
        <condition field="destination_number" expression="[\d]{7,}?$">
                <action application="set" data="effective_caller_id_number=10000"/>
                <action application="bridge" data="sofia/gateway/gw/$1"/>
        </condition>
    </extension>

the dialplan runs well and when FS has to bridge the call it opens a channel
to "sofia/gateway/gw/$1", it does not replace the $1 by the actual number
being dialed, i have the same in other parts of the dialplan and it works
good, i can not find what i m doing wrong here, i would appreciate any hint
about this issue. 
thanks!