One approach is to put all the config files in a single directory and then you call logstash like this:
logstash -f path_to_directory
BUT, in order for this to work, in each config file you need to use types as shown below. Each config file must have a different type or else the config files will step on each other.
input {
-your normal input settings-
type => "my_type_1"
}
filter {
if [type] == "my_type_1"{
-your normal filter settings-
}
}
output {
if [type] == "my_type_1" {
-your normal output settings-
}
}