Question

I need to know how many processes are running for a specific task (e.g. number of Apache tomcats) and if it’s 1, then print the PID. Otherwise print out a message.

I need this in a BASH script, now when I perform something like:

result=`ps aux | grep tomcat | awk '{print $2}' | wc -l`

The number of items is assigned to result. Hurrah! But I don’t have the PID(s). However when I attempt to perform this as an intermediary step (without the wc), I encounter problems. So if I do this:

result=`ps aux | grep tomcat | awk '{print $2}'`

Any attempts I make to modify the variable result just don’t seem to work. I’ve tried set and tr (replace blanks with line-breaks), but I just cannot get the right result. Ideally I’d like the variable result to be an array with the PIDs as individual elements. Then I can see size, elements, easily.

Can anyone suggest what I am doing wrong?
Thanks,
Phil

Update:

I ended up using the following syntax:

pids=(`ps aux | grep "${searchStr}"| grep -v grep | awk '{print $2}'`)
number=${#pids[@]}

The key was putting the brackets around the back-ticked commands. Now the variable pids is an array and can be asked for length and elements.

Thanks to both choroba and Dimitre for their suggestions and help.

Answer 1

pids=($(
    ps -eo pid,command |
    sed -n '/[t]omcat/{s/^ *\([0-9]\+\).*/\1/;p}'
))
number=${#pids[@]}

pids=( ... ) creates an array.
$( ... ) returns its output as a string (similar to backquote).
Then, sed is called on the list of all the processes: for lines containing tomacat (the [t] prevents the sed itself from being included), only the pid is preserved and printed.