selecting only required lines from unix shell prompt

Lets say I am running

$: p开发者_开发问答s au

in a shell prompt and want to select 2nd field of 5th entry in that, no matter which process it is. How do I do that ?

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With awk.

awk 'NR==6 { print $2 }'

The 6th record because you need to skip the header.

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If you don't want to use awk or the equivalent perl or ruby commands, you can also use more low-level tools:

ps au | head -6 | tail -1 | cut -d ' ' -f 2

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In "ps au" output, second field is the process ID; you can extract it directly by telling to ps what you need:

ps a -o pid=

Then you just need to output the fifth line:

ps a -o pid= | sed '5!d'