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I'm trying to write a little diagnostic tool and one of the functions I want from it is that I want to run is:

ps axu | grep tomcat | grep -v grep | awk '{ print $<list of desired fields> }'  

I want to return the userid that started tomcat and the following parameters that were passed when tomcat started:

-javaagent:/usr/share/tomcat7/<someagent> -Dcatalina.base=/var/lib/tomcat7 
- Dcatalina.home=/usr/share/tomcat7 -Djava.io.tmpdir=/tmp/tomcat7-tomcat7-tmp

I want those fields passed into an array which I can then use to tell the user something about the tomcat install.

The problem is I can't find a way of formatting the command to force the fields to be what I need them to be to make awk work.

At this point I'm thinking of just taking the output, writing it to a temp file, then pulling what I want out using regex.

I know there's a way to do this in Bash but I have not had any success getting there from here.

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It needs to be from ps output? –  Braiam Aug 10 at 23:49
    
I should clarify something. This is a tech support tool that will be provided to customers and so I can't know in advance what form of *NIX they'll be running ahead of time. It occurred to me that there's another way to get at it. Since this is meant to be used by other IT people I thought I could just build a menu and just ask them for their OS which I could then pass the appropriate ps command for. If that is a worse idea than the one before, let me know. I appreciate the feedback y'all have given me so far. It's been invaluable. –  Adrienne Davis Aug 11 at 0:14
    
@AdrienneDavis Don't ask the user to do something that can easily be done automatically! You can detect the OS automatically — but you don't need to, you can just stick to standard features (as I do in my answer). –  Gilles Aug 11 at 7:19

2 Answers 2

Pass the -o option to ps to control which fields it outputs. If you add an = sign after all the fields, then the header line is omitted.

Use -e instead of ax to stick to standard features (this will work on any non-antique unix).

Your filter with grep is not robust. For example, if you run this command from a script called look-for-tomcat, then your script would be matched as well. Here's a more robust way that looks for a JVM process with org.apache.catalina.startup.Bootstrap as an argument.

ps -e -o user=,args= | awk '
    $2 ~ /java$/ &&  / org\.apache\.catalina\.startup\.Bootstrap($| ) {
        print "user name: ", $1;
        if (match($0, / -javaagent:[^ ]* /)) print substr($0, RSTART+1, RSTART+RLENGTH-2);
        # etc.
    }'

Even better would be to log the PID of the tomcat process in a file (e.g. /var/run/tomcat.pid) when it starts.

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If you have /proc on your particular flavor of *nix, you may try to coax the data you want out of that instead. I think this may be a bit saner than attempting to wade through the tedium of parsing output that is meant for a human to read.

For example, to get the user ID that started the tomcat process, you can do:

stat -c'%u' /proc/$(pgrep tomcat)/

Relying on the availability (and standardization) of /proc may be even more of a hassle depending on your particular application/environment/... It's up to you to decide, I guess.

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