HTTP redirect with different URIs

Kai, You're right. the "&" must be replaced by "?" in the irule...

For the "string range" vs "string map", I'm no sure is it better to use string range. I checked performance of tcl code with tclsh:

-- Provisioning of variables:

% set uri "/sites/pmo?test=toto&foo=bar"
/sites/pmo?test=toto&foo=bar
% set path /sites/pmo
/sites/pmo
% set query "test=toto&foo=bar"
test=toto&foo=bar

-- Test of code:

% set new_uri "http://www.xyz.com/is[string range $uri 6 end]"
http://www.xyz.com/is/pmo?test=toto&foo=bar
% set new_uri "http://www.xyz.com[string map {/sites/pmo /is/pmo} $path]?$query"
http://www.xyz.com/is/pmo?test=toto&foo=bar

-- Performance of string range:

% time { set new_uri "http://www.xyz.com/is[string range $uri 6 end]"} 10000
2.9012927 microseconds per iteration
% time { set new_uri "http://www.xyz.com/is[string range $uri 6 end]"} 10000
2.9444715 microseconds per iteration

-- Performance of string map:

% time {set new_uri "http://www.xyz.com[string map {/sites/pmo /is/pmo} $path]?$query"} 10000
2.8971892 microseconds per iteration
% time {set new_uri "http://www.xyz.com[string map {/sites/pmo /is/pmo} $path]?$query"} 10000
2.9607483 microseconds per iteration

But I agree that your code does not add a "?" if there is no query string.