Ubuntu – Get specific PID and save to file

awkgrepps

I'm running two minecraft servers on my machine. I want to know what the pid is of a single mc server that is running and put it to file so that I can kill it later. So for this example I only want to know what the PID is of World2 nothing else and save it to file.

When I perform a command 

ps h -o pid,cmd -u minecraft

I get the following results

31416 /usr/lib/jvm/java-8-oracle/jre/bin/java -Xmx2G -Xms1G -jar /data/mc-server/World1/minecraft_server.jar nogui
31706 /usr/lib/jvm/java-8-oracle/jre/bin/java -Xmx6G -Xms4G -jar /data/mc-server/World2/craftbukkit.jar nogui

I then pipe to grep using this command

grep World2

This is where I get into difficulties, I then pipe to to get a single result back. I tried the following but just can't get it.

awk '{print $1 > world2.pid}'

So my full command is:

ps h -o pid,cmd -u minecraft | grep World2 | awk '{print $1 > world2.pid}'

I get the following error:

awk: cmd. line:1: {print $1 > world2.pid}
awk: cmd. line:1:                 ^ syntax error

Best Answer

If you want to put the redirection inside awk, you need to put the filename in quotes - otherwise, awk treats it as a variable rather than a literal string:

... | awk '{print $1 > "world2.pid"}'

However it would be more conventional to let awk write to standard output, and redirect that i.e.

... | awk '{print $1}' > world2.pid

Alternatively, you may want to look at using pgrep for the whole task e.g. something like

pgrep -f 'World2' > world2.pid
Related Question