irule redirect by url.

You're technically correct, but I would put the switch conditions inside double quotes.

when HTTP_REQUEST {     
    switch -glob [string tolower [HTTP::host]] { 
        "a-mysite.zcorp.com" {
            pool a-mysite-pool
        } 
        "b-mysite.zcorp.com" { 
            pool b-mysite-pool
        }
        "c-mysite.zcorp.com" {
            pool c-mysite-pool
        }
        "b-mysite.zcorp.com" {
            pool d-mysite-pool
        } 
        "e-mysite.zcorp.com" { 
            pool e-mysite-pool
        } 
        default {
            reject 
        } 
    } 
}