Example...

input { file { type => "apachelog" path => ["C:/logs/apachelogs.log"] start_position => "beginning" }
}
filter {
if [type] == "apachelog" { grok { match => {"message" => '%{IPORHOST:clientip} %{USER:ident} %{USER:auth} \[%{HTTPDATE:timestamp}\] "(?:%{WORD:verb} %{NOTSPACE:request}(?: HTTP/%{NUMBER:httpversion})?|%{DATA:rawrequest})" %{NUMBER:response} (?:%{NUMBER:bytes}|-)'} } }
}