grep -Z

from grep manual in debian.

Output a zero byte (the ASCII NUL character) instead of the character that normally follows a file name

$grep  -Z FACK  *
proc.c  SNMP_MIB_ITEM("TCPFACKReorder", LINUX_MIB_TCPFACKREORDER),
sysctl_net_ipv4.c               .ctl_name       = NET_TCP_FACK,
tcp_input.c * Packet counting of FACK is based on in-order assumptions, therefore TCP
tcp_input.c                     mib_idx = LINUX_MIB_TCPFACKREORDER;
tcp_input.c *      A''. Its FACK modfication, head until snd.fack is lost.
tcp_input.c * Event "C". Later note: FACK people cheated me again 8), we have to account
tcp_input.c              * Whether FACK should check here for tp->reordering segs
tcp_input.c * Instead, with FACK TCP uses fackets_out that includes both SACKed
tcp_input.c/* Linux NewReno/SACK/FACK/ECN state machine.
tcp_input.c *           FACK: It is the simplest heuristics. As soon as we decided
tcp_input.c *           takes place. We use FACK by default until reordering
tcp_output.c * based retransmit packet might feed us FACK information again.
tcp_vegas.c *     using fine-grained timers, NewReno, and FACK.




$grep  FACK  *
proc.c: SNMP_MIB_ITEM("TCPFACKReorder", LINUX_MIB_TCPFACKREORDER),
sysctl_net_ipv4.c:              .ctl_name       = NET_TCP_FACK,
tcp_input.c: * Packet counting of FACK is based on in-order assumptions, therefore TCP
tcp_input.c:                    mib_idx = LINUX_MIB_TCPFACKREORDER;
tcp_input.c: *     A''. Its FACK modfication, head until snd.fack is lost.
tcp_input.c: * Event "C". Later note: FACK people cheated me again 8), we have to account
tcp_input.c:             * Whether FACK should check here for tp->reordering segs
tcp_input.c: * Instead, with FACK TCP uses fackets_out that includes both SACKed
tcp_input.c:/* Linux NewReno/SACK/FACK/ECN state machine.
tcp_input.c: *          FACK: It is the simplest heuristics. As soon as we decided
tcp_input.c: *          takes place. We use FACK by default until reordering
tcp_output.c: * based retransmit packet might feed us FACK information again.
tcp_vegas.c: *     using fine-grained timers, NewReno, and FACK.
$