State machine

record_proc.awk

function get_state() {
    return substr($0,1,1)
}
BEGIN {
    #state machine spec
    start_state="_BOF_"
    state["_BOF_"]="H"
    state["H"]="B"
    state["B"]="D"
    state["D"]="B|D|T"
    state["T"]="_EOF_"
    state["_EOF_"]="_BOF_"
    final_states="_EOF_"
}

run.sh

awk -f state_machine.awk -f record_proc.awk test
# test:6: State transition not present: B -> B
# test:7: State transition not present: B -> T

state_machine.awk

# you must implement get_state elsewhere.
function validate_state() {
    transitions_str = state[previous_state]
    split(transitions_str, transitions_ary, "|")
    for (key in transitions_ary) {
        if (transitions_ary[key] == current_state) {
            return 1
        }
    }
    return 0
}

BEGIN {
    current_state = "_BOF_"
}

{
    previous_state=current_state
    current_state=get_state()
    if (!validate_state()) {
        print FILENAME":"FNR": State transition not present: "previous_state" -> "current_state > "/dev/stderr"
        #exit 1
    }
}

test

H
B
D
D
B
B error (should be D)
T