bash - How to create an anonymous pipe between 2 child processes and know their pids (while not using files/named pipes)? -

please note questions edited after couple of comments received. wanted split goal smaller pieces make simpler (and perhaps expand knowledge on various fronts), seems went far simplicity :). so, here asking big question.

using bash, there way 1 can create anonymous pipe between 2 child processes , know pids?

the reason i'm asking when use classic pipeline, e.g.

cmd1 | cmd2 & 

you lose ability send signals cmd1. in case actual commands running these

./my_web_server | ./my_log_parser & 

my_web_server basic web server dump lot of logging information it's stdout my_log_parser log parser wrote reads through logging information receives my_web_server , selects values log (in reality stores whole log received it, additionally creates csv file values finds).

the issue having my_web_server never stops (it web server, don't want web server :)). after done, need stop myself. bash script when stop (the bash script), either via sigint or sigterm.

for this, traps way go. in essence create trap int , term , function call kill my_web_server, but... don't have pid , though know via ps, looking pretty solution :).

some of might say: "well, why don't kill my_log_parser , let my_web_server die on own sigpipe?". reason why don't want kill when kill process that's @ end of pipeline, output buffer of process before it, not flushed. ergo, lose stuff.

i've seen several solutions here , in other places suggested store pid of my_web_server in file. solution works. possible write pipeline fiddling filedescriptors bit. i, don't solution, because have generate files. don't idea of creating arbitrary files store 5-character pid :).

what ended doing this:

#!/bin/bash  trap " " hup  fifo="$( mktemp -u "$( basename "${0}" ).xxxxxx" )" mkfifo "${fifo}"  <"${fifo}" ./my_log_parser & parser_pid="$!"  >"${fifo}" ./my_web_server & server_pid="$!"  rm "${fifo}"  trap '2>/dev/null kill -term '"${server_pid}"'' int term  while true;   wait "${parser_pid}" && break done 

this solves issue me not being able terminate my_web_server when script receives sigint or sigterm. seems more readable hackery fiddling file descriptors in order use file store my_web_server's pid, think good, because improves readability.

but still uses file (named pipe). though know uses file (named pipe) my_web_server , my_log_parser talk (which pretty reason) , file gets wiped disk shortly after it's created, it's still file :).

would of guys know of way task without using files (named pipes)?

from bash man pages:

!      expands    process id of executed back-        ground (asynchronous) command. 

you not running background command, running process substitution read file descriptor 3.

the following works, i'm not sure if trying achieve:

sleep 120 & child_pid="$!"  wait "${child_pid}" sleep 120 

edit: comment was: i know can pretty silly 'while read i; blah blah; done < <( ./my_proxy_server )'-way, don't particularly fact when script using approach receives int or term, dies without telling ./my_proxy_server bugger off :)

so, seems problem stems fact not easy pid of proxy server. so, how using own named pipe, trap command:

pipe='/tmp/mypipe' mkfifo "$pipe" ./my_proxy_server > "$pipe" &  child_pid="$!" echo "child pid $child_pid"  # tell proxy server bugger-off trap 'kill $child_pid' int term  while read     echo $reply     # blah blah blah done < "$pipe"  rm "$pipe" 

you use kill %1 instead of using $child_pid.

yae (yet edit):
ask how pids from:

./my_web_server | ./my_log_parser & 

simples, sort of. test used sleep, original.

sleep 400 | sleep 500 & jobs -l 

gives:

[1]+  8419 running                 sleep 400       8420 running                 | sleep 500 & 

so question of extracting pids:

pid1=$(jobs -l|awk 'nr==1{print $2}') pid2=$(jobs -l|awk 'nr==2{print $1}') 

i hate calling awk twice here, else jumping through hoops.