I want to run nc via & and then manually feed data in stdin from /proc filesystem whenever I want. so the problem is:
if I run nc 127.0.0.1 1234 &
program runs in background and I can write in stdin whatever I want. but, if I create test.sh and add
#!/bin/bash
nc 127.0.0.1 1234 &
sleep 20
it connects to 1234 and terminates immediately (doesn't even wait for 20 seconds). why? I was suspecting it gets it's stdin written from somewhere.
If I get your purpose right, you want to feed data manually to nc which will be sent to client.
You can use named pipes for this purpose.
cat /tmp/f | ./parser.sh 2>&1 | nc -lvk 127.0.0.1 1234 > /tmp/f
where /tmp/f is a pipe made using mkfifo /tmp/f
whatever you want to feed to nc can be echo-ed in parser.sh
Interesting question.
The bash manpage states:
If a command is followed by a & and job control is not active, the
default standard input for the command is the empty file /dev/null.
Otherwise, the invoked command inherits the file descriptors of the
calling shell as modified by redirections.
If you call nc 127.0.0.1 1234 < /dev/null outside a shell script (with job control) it will result in the same.
You can change your bash script like this to make it work:
#!/bin/bash
nc 127.0.0.1 1234 < /dev/stdin &
sleep 20