Send command to a background process

Based on the answers:

1. Writing to stdin of background process
2. Accessing bash command line args $@ vs $*
3. Why my named pipe input command line just hangs when it is called?
4. Can I redirect output to a log file and background a process at the same time?

I wrote two shell scripts to communicate with my game server.

This first script is run when computer start up. It does start the server and configure it to read/receive my commands while it run in background:

start_czero_server.sh

#!/bin/sh # Go to the game server application folder where the game application `hlds_run` is cd /home/user/Half-Life # Set up a pipe named `/tmp/srv-input` rm /tmp/srv-input mkfifo /tmp/srv-input # To avoid your server to receive a EOF. At least one process must have # the fifo opened in writing so your server does not receive a EOF. cat > /tmp/srv-input & # The PID of this command is saved in the /tmp/srv-input-cat-pid file # for latter kill. # # To send a EOF to your server, you need to kill the `cat > /tmp/srv-input` process # which PID has been saved in the `/tmp/srv-input-cat-pid file`. echo $! > /tmp/srv-input-cat-pid # Start the server reading from the pipe named `/tmp/srv-input` # And also output all its console to the file `/home/user/Half-Life/my_logs.txt` # # Replace the `./hlds_run -console -game czero +port 27015` by your application command ./hlds_run -console -game czero +port 27015 > my_logs.txt 2>&1 < /tmp/srv-input & # Successful execution exit 0 

This second script it just a wrapper which allow me easily to send commands to the my server:

send.sh

half_life_folder="/home/jack/Steam/steamapps/common/Half-Life" half_life_pid_tail_file_name=hlds_logs_tail_pid.txt half_life_pid_tail="$(cat $half_life_folder/$half_life_pid_tail_file_name)" if ps -p $half_life_pid_tail > /dev/null then echo "$half_life_pid_tail is running" else echo "Starting the tailing..." tail -2f $half_life_folder/my_logs.txt & echo $! > $half_life_folder/$half_life_pid_tail_file_name fi echo "$@" > /tmp/srv-input sleep 1 exit 0 

Now every time I want to send a command to my server I just do on the terminal:

./send.sh mp_timelimit 30 

This script allows me to keep tailing the process on your current terminal, because every time I send a command, it checks whether there is a tail process running in background. If not, it just start one and every time the process sends outputs, I can see it on the terminal I used to send the command, just like for the applications you run appending the & operator.

You could always keep another open terminal open just to listen to my server server console. To do it just use the tail command with the -f flag to follow my server console output:

./tail -f /home/user/Half-Life/my_logs.txt 

If you don't want to be limited to signals, your program must support one of the Inter Process Communication methods. See the corresponding Wikipedia article.

A simple method is to make it listen for commands on a Unix domain socket.

For how to send commands to a server via a named pipe (fifo) from the shell see here:

Redirecting input of application (java) but still allowing stdin in BASH

How do I use exec 3>myfifo in a script, and not have echo foo>&3 close the pipe?

You can use the bash's coproc comamnd. (avaliable only in 4.0+) - it's like ksh's |&

check this for examples http://wiki.bash-hackers.org/syntax/keywords/coproc

you can't send new args to a running process.

But if you are implementing this process or its a process that can take the args from a pipe, then the other answer would help.