bash: split output of command by columns

Question

I want to do this:

1. run a command
2. capture the output
3. select a line
4. select a column of that line

Just as an example, let's say I want to get the command name from a $PID (please note this is just an example, I'm not suggesting this is the easiest way to get a command name from a process id - my real problem is with another command whose output format I can't control).

If I run ps I get:

  PID TTY          TIME CMD
11383 pts/1    00:00:00 bash
11771 pts/1    00:00:00 ps

Now I do ps | egrep 11383 and get

11383 pts/1    00:00:00 bash

Next step: ps | egrep 11383 | cut -d" " -f 4. Output is:

<absolutely nothing/>

The problem is that cut cuts the output by single spaces, and as ps adds some spaces between the 2nd and 3rd columns to keep some resemblance of a table, cut picks an empty string. Of course, I could use cut to select the 7th and not the 4th field, but how can I know, specially when the output is variable and unknown on beforehand.

Answer 1

Getting the correct line (example for line no. 6) is done with head and tail and the correct word (word no. 4) can be captured with awk:

command|head -n 6|tail -n 1|awk '{print $4}'

Answer 2

I think the simplest way is to use awk. Example:

$ echo "11383 pts/1    00:00:00 bash" | awk '{ print $4; }'
bash

Answer 3

One easy way is to add a pass of tr to squeeze any repeated field separators out:

$ ps | egrep 11383 | tr -s ' ' | cut -d ' ' -f 4

Answer 4

try

ps |&
while read -p first second third fourth etc ; do
   if [[ $first == '11383' ]]
   then
       echo got: $fourth
   fi       
done

Answer 5

Instead of doing all these greps and stuff, I'd advise you to use ps capabilities of changing output format.

ps -o cmd= -p 12345

You get the cmmand line of a process with the pid specified and nothing else.

This is POSIX-conformant and may be thus considered portable.