Need advice for using nested command subsitution

Question

I'm trying to wrap my head around nested command substitution. I tried nesting backticks but obviously that doesn't work. How would you nest the following without declaring the ${host} variable first?

host=$(hostname|cut -c1-14);for id in `aladmin list|grep ${host}|awk '{print $2}'`;do aladmin delete ${id};done

The command lists all alarms on a server, greps for the first 14 characters of the hostname and then deletes the alarm with the alarm ID found in field 2 by awk.

My question does in no way duplicate the 'hello' in previous post: How to properly nest Bash backticks

Thanks in advance, Bjoern

`grep ... | awk` is an anti-pattern – William Pursell Nov 19 '20 at 15:29 — William Pursell, Nov 19 '20 at 15:29

score 0 · Answer 1 · answered Nov 19 '20 at 15:39

0

Do everything in awk. There's no need to use the for loop and the grep, etc. There are better ways than this, but as a first approximation, try something like:

aladmin list | awk "/$(hostname | cut -c1-14)/"'{ print "aladmin delete " $2 | "sh"}'

answered Nov 19 '20 at 15:39

William Pursell

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You could probably remove the need for cut through using awk's substr as well. – Raman Sailopal Dec 09 '20 at 14:23
Yes, that winds up looking something like: `awk '$0 ~ substr(h, 1, 14){ print "aladmin delete " $2 | "sh"}' h=$(hostname)` – William Pursell Dec 09 '20 at 14:58

Need advice for using nested command subsitution

1 Answers1