Bash if statement with input from another command

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I am fairly new to shell scripting so kindly bear with me. Here is what I want to do : Check the sar logs captured on a Linux server and if the load average for the past 1 minute is greater than the number of CPUs, print that load info. I used the following command for this:

awk '/runq-sz/,/$^/' /var/log/sa/sar* | awk '{print $5}' \
| awk '{if ($1 > **CPU_COUNT**) print $0}' \
| grep -iv "ldavg" | head -n5

Ex, for a server with 16 CPUs:

awk '/runq-sz/,/$^/' /var/log/sa/sar* | awk '{print $5}' \
| awk '{if ($1 > **16**) print $0}' | grep -iv "ldavg" \
| head -n5

I get the following output which is correct and shows the command is working.

18.11
73.91
40.03
40.77
33.85

But what if instead of hardcoding CPU_COUNT, use a built-in Linux command like nproc? Is it possible to do so? If yes, how do I use it? I tried with something like this:

awk '/runq-sz/,/$^/' /var/log/sa/sar* | awk '{print $5}' \
| awk '{if ($1 > echo "$(nproc)") print $0}' \
| grep -iv "ldavg"

But it doesn’t appear to be working. Am I missing something here? If this approach is incorrect how do I change the command?

  • 1

    Does this answer your question? How do I use shell variables in an awk script?

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  • do something like amount=$(....command-to-get-n-count...) and then pass that one to awk as shown in the marked duplicate.

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  • if N > echo.... is certainly not a valid numeric comparision in awk. Have a look at awk’s -v option, which allows you to set awk variables when invoking awk.

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  • 2

    You don’t need all those separate commands and pipelines for this, just 1 awk command will do. Post a minimal reproducible example including concise, testable sample input and expected output so we can help you do this the right way.

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  • 1

    BTW, it’s pretty much never necessary to pipe from awk to grep or head; awk itself can do the work of both those tools. In the case of grep, use /ldavg/ {next} to skip lines that contain ldavg; in the case of head, use NR > 5 { exit }

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You’re on the right track, but you’re trying to use echo $(nproc) within awk, which won’t work as expected. You need to pass the output of nproc to awk as a variable. You can do this using the -v option in awk. Here’s how you can modify your command:

awk -v cpu_count=$(nproc) '/runq-sz/,/$^/' /var/log/sa/sar* | awk -v cpu_count="$cpu_count" '{if ($1 > cpu_count) print $0}' | grep -iv "ldavg" | head -n5

This should give you the desired output, with the number of CPUs dynamically determined by nproc.

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