Bash piping output and input of a program

I'm running a minecraft server on my linux box in a detached screen session. I'm not very fond of screen very much and wo开发者_高级运维uld like to be able to constantly pipe the output of the server to a file(like a pipe) and pipe some input from a file to the server(so that I can input and output to the server from remote programs, like a python script). I'm not very experienced in bash, so could somebody tell me how to do this?

Thanks, NikitaUtiu.

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It's not clear if you need screen at all. I don't know the minecraft server, but generally for server software, you can run it from a crontab entry and redirect output to log files.

Assuming your server kills itself at midnight sunday night, (we can discuss changing this if restarting 1x per week is too little or too much OR you require ad-hoc restarts), but for a basic idea of what to do, here is a crontab entry that starts the server each monday at 1 minute after midnight.

01 00 * * 1 dtTm=`/bin/date +\%Y\%m\%d.\%H\%M\%S`; export dtTm; {  /usr/bin/mineserver -o ..... your_options_to_run_mineserver_here ... ; } > /tmp/mineserver_trace_log.${dtTm} 2>&1

consult your man page for crontab to confirm that day-of-week ranges are 0-6 (0=Sunday), and change the day-of-week value if 0!=Sunday.

Normally I would break the code up so it is easier to read, but for crontab entries, each entry has to be all on one line, (with some weird exceptions) AND usually a limit of 1024b-8K to how long the line can be. Note that the ';' just before the closing '}' is super-critical. If this is left out, you'll get un-deciperable error messages, or no error messages at all.

Basically, you're redirecting any output into a file (including std-err output). Now you can do a lot of stuff with the output, use more or less to look at the file, grep ERR ${logFile}, write scripts that grep for error messages and then send you emails that errors have been found, etc, etc.

You may have some sys-admin work on your hands to get the mineserver user so it can run crontab entries. Also if you're not comfortable using the vi or emacs editors, creating a crontab file may require help from others. Post to superuser.com to get answers for problems you have with linux admin issues.

Finally, there are two points I'd like to make about dated logfiles.

1. Good: a. If you app dies, you never have to rerun it to then capture output and figure out why something has stopped working. For long running programs this can save you a lot of time. b. keeping dated files gives you the ability to prove to you, your boss, others, that It used to work just fine, see here are the log files. c. Keeping the log files, assuming there is useful information in them, gives you the opportunity to mine those files for facts. I.E. : program used to take 1 sec for processing, now it is taking 1 hr, etc etc.

2. Bad: a. You'll need to set up a mechanism to sweep old log files, otherwise at some point everything will have stopped, AND when you finally figure out what the problem was, you discover that your /tmp OR whatever dir you chose to use IS completely full.

There is a self-maintaining solution to using dates on the logfiles I can tell you about if you find this approach useful. It will take a little explaining, so I don't want to spend the time writing it up if you don't find the crontab solution useful.

I hope this helps!