stateful awk

#!/bin/bash

# Demonstrates how awk can operate stateful across multiple lines


tstfile="$(mktemp)"

exec 3>"$tstfile"
echo Garbage >&3
echo HEADER1 >&3
echo Garbage >&3
echo Garbage >&3
echo Garbage >&3
echo TIMESTAMP1 >&3
echo Garbage >&3
echo Garbage >&3
echo Garbage >&3
echo MATCH1 >&3
echo Garbage >&3
echo HEADER1 >&3
echo Garbage >&3
echo Garbage >&3
echo Garbage >&3
echo TIMESTAMP1 >&3
echo Garbage >&3
echo Garbage >&3
echo Garbage >&3
echo MATCH2 >&3

exec 3>&-

awk '
function clear_state() { header=""; timestamp="" }
BEGIN{ clear_state() }
/^HEADER/{ clear_state(); header=$0 }
header && /^TIMESTAMP/{ timestamp=$0 }
header && timestamp && /^MATCH1/ {
    printf("%s @ %s: %s\n", header, timestamp, $0);
    clear_state()
}
header && timestamp && /^MATCH2/ {
    print($0);
    clear_state();
}
' <"$tstfile"

unlink "$tstfile"