How can I close a netcat connection after a certain character is returned in the response?

Create a bash script called client.sh:

#!/bin/bashcat someFilewhile read FOO; do        echo $FOO >&3        if [[ $FOO =~ `printf ".*\x00\x1c.*"` ]]; then                break        fidone

Then invoke netcat from your main script like so:

3>&1 nc -c ./client.sh somehost 1234

(You'll need bash version 3 for the regexp matching).

This assumes that the server is sending data in lines - if not you'll have to tweak client.sh so that it reads and echoes a character at a time.

How about this?

Client side:

awk -v RS=$'\x1c' 'NR==1;{exit 0;}'  < /dev/tcp/host-ip/port

Testing:

# server side test scriptwhile true; do ascii -hd; done | { netcat -l 12345; echo closed...;}# Generate 'some' data for testing & pipe to netcat.# After netcat connection closes, echo will print 'closed...'# Client side:awk -v RS=J 'NR==1; {exit;}' < /dev/tcp/localhost/12345# Changed end character to 'J' for testing.# Didn't wish to write a server side script to generate 0x1C.

Client side produces:

    0 NUL    16 DLE    32      48 0    64 @    80 P    96 `   112 p    1 SOH    17 DC1    33 !    49 1    65 A    81 Q    97 a   113 q    2 STX    18 DC2    34 "    50 2    66 B    82 R    98 b   114 r    3 ETX    19 DC3    35 #    51 3    67 C    83 S    99 c   115 s    4 EOT    20 DC4    36 $    52 4    68 D    84 T   100 d   116 t    5 ENQ    21 NAK    37 %    53 5    69 E    85 U   101 e   117 u    6 ACK    22 SYN    38 &    54 6    70 F    86 V   102 f   118 v    7 BEL    23 ETB    39 '    55 7    71 G    87 W   103 g   119 w    8 BS     24 CAN    40 (    56 8    72 H    88 X   104 h   120 x    9 HT     25 EM     41 )    57 9    73 I    89 Y   105 i   121 y   10 LF     26 SUB    42 *    58 :    74

After 'J' appears, server side closes & prints 'closed...', ensuring that the connection has indeed closed.

Try:

(cat somefile; sleep $timeout) | nc somehost 1234 | sed -e '{s/\x01.*//;T skip;q;:skip}'

This requires GNU sed.

How it works:

{    s/\x01.*//; # search for \x01, if we find it, kill it and the rest of the line    T skip;     # goto label skip if the last s/// failed    q;          # quit, printing current pattern buffer    :skip       # label skip}

Note that this assumes there'll be a newline after \x01 - sed won't see it otherwise, as sed operates line-by-line.