Question

Hi I need an script to read number of eth interrupts from the /proc/interrupts file with awk and find the total number of interrupts per CPU core.An then I want to use them in bash.The content of the file is;

      CPU0       CPU1       CPU2       CPU3

47:   33568      45958      46028      49191     PCI-MSI-edge    eth0-rx-0
48:     0          0          0          0       PCI-MSI-edge      eth0-tx-0
49:     1          0          1          0       PCI-MSI-edge      eth0
50:   28217      42237      65203      39086     PCI-MSI-edge    eth1-rx-0
51:     0          0          0          0       PCI-MSI-edge      eth1-tx-0
52:     0          1          0          1       PCI-MSI-edge      eth1
59:     114991     338765      77952     134850  PCI-MSI-edge eth4-rx-0
60:     429029     315813     710091      26714  PCI-MSI-edge eth4-tx-0
61:      5          2          1          5      PCI-MSI-edge     eth4
62:    1647083     208840    1164288     933967  PCI-MSI-edge eth5-rx-0
63:     673787    1542662     195326    1329903  PCI-MSI-edge eth5-tx-0
64:     5          6          7          4       PCI-MSI-edge      eth5

I am reading this file with awk in this code:

#!/bin/bash

 FILE="/proc/interrupts"

 output=$(awk 'NR==1 {
 core_count = NF 
 print core_count
 next
}
/eth/ {
 for (i = 2; i <= 2+core_count; i++)
 totals[i-2] += $i
}

END {
 for (i = 0; i < core_count; i++)
 printf("%d\n", totals[i])
}
' $FILE)

core_count=$(echo $output | cut -d' ' -f1)

output=$(echo $output | sed 's/^[0-9]*//')

totals=(${output// / })

In this approach, I handle the total core count and then the total interrupts for per CORE in order to sort them in my script.But I can only handle the number in totals array lke this,

    totals[0]=22222
    totals[1]=33333

But I need to handle them as tuple with the name of the CPU cores.

    totals[0]=(cPU1,2222)
    totals[1]=(CPU',3333)

I think I must assign the names to an array and read themn to bash as tuples in my SED. How can I achieve this?

Answer 1

First of all, there’s no such thing as a ‘tuple’ in bash. And arrays are completely flat. It means that you either have a ‘scalar’ variable, or one level array of scalars.

There is a number approaches to the task you’re facing. Either:

1. If you’re using a new enough bash (4.2 AFAIR), you can use an associative array (hash, map or however you call it). Then, the CPU names will be keys and the numbers will be values;
2. Create a plain array (perl-like hash) where odd indexes will have the keys (CPU names) and even ones — the values.
3. Create two separate arrays, one with the CPU names and other with the values,
4. Create just a single array, with CPU names separated from values by some symbol (i.e. = or :).

---

Let’s cover approach 2 first:

#!/bin/bash

FILE="/proc/interrupts"

output=$(awk 'NR==1 {
    core_count = NF
    for (i = 1; i <= core_count; i++)
        names[i-1] = $i
    next
}
/eth/ {
    for (i = 2; i <= 2+core_count; i++)
        totals[i-2] += $i
}

END {
    for (i = 0; i < core_count; i++)
        printf("%s %d\n", names[i], totals[i])
}
' ${FILE})

core_count=$(echo "${output}" | wc -l)
totals=(${output})

Note a few things I’ve changed to make the script simpler:

1. awk now outputs `cpu-name number’, one per line, separated by a single space;
2. the core count is not output by awk (to avoid preprocessing output) but instead deduced from number of lines in the output,
3. the totals array is created by flattening the output — both spaces and newlines will be treated as whitespace and use to separate the values.

The resulting array looks like:

totals=( CPU0 12345 CPU1 23456 ) # ...

To iterate over it, you could use something like (the simple way):

set -- "${totals[@}}"
while [[ $# -gt 0 ]]; do
    cpuname=${1}
    value=${2}

    # ...

    shift;shift
done

---

Now let’s modify it for approach 1:

#!/bin/bash

FILE="/proc/interrupts"

output=$(awk 'NR==1 {
    core_count = NF
    for (i = 1; i <= core_count; i++)
        names[i-1] = $i
    next
}
/eth/ {
    for (i = 2; i <= 2+core_count; i++)
        totals[i-2] += $i
}

END {
    for (i = 0; i < core_count; i++)
        printf("[%s]=%d\n", names[i], totals[i])
}
' ${FILE})

core_count=$(echo "${output}" | wc -l)
declare -A totals
eval totals=( ${output} )

Note that:

1. the awk output format has been changed to suit the associative array semantics,
2. totals is declared as an associative array (declare -A),
3. sadly, eval must be used to let bash directly handle the output.

The resulting array looks like:

declare -A totals=( [CPU0]=12345 [CPU1]=23456 )

And now you can use:

echo ${totals[CPU0]}

for cpu in "${!totals[@]}"; do
    echo "For CPU ${cpu}: ${totals[${cpu}]}"
done

---

The third approach can be done a number of different ways. Assuming you can allow two reads of /proc/interrupts, you could even do:

FILE="/proc/interrupts"

output=$(awk 'NR==1 {
    core_count = NF
    next
}
/eth/ {
    for (i = 2; i <= 2+core_count; i++)
        totals[i-2] += $i
}

END {
    for (i = 0; i < core_count; i++)
        printf("%d\n", totals[i])
}
' ${FILE})

core_count=$(echo "${output}" | wc -l)
names=( $(cat /proc/interrupts | head -n 1) )
totals=( ${output} )

So, now the awk is once again only outputting the counts, and names are obtained by bash from first line of /proc/interrupts directly. Alternatively, you could create split arrays from a single array obtained in approach (2), or parsing the awk output some other way.

The result would be in two arrays:

names=( CPU0 CPU1 )
totals=( 12345 23456 )

And output:

for (( i = 0; i < core_count; i++ )); do
    echo "${names[$i]} -> ${totals[$i]}"
done

---

And the last approach:

#!/bin/bash

FILE="/proc/interrupts"

output=$(awk 'NR==1 {
    core_count = NF
    for (i = 1; i <= core_count; i++)
        names[i-1] = $i
    next
}
/eth/ {
    for (i = 2; i <= 2+core_count; i++)
        totals[i-2] += $i
}

END {
    for (i = 0; i < core_count; i++)
        printf("%s=%d\n", names[i], totals[i])
}
' ${FILE})

core_count=$(echo "${output}" | wc -l)
totals=( ${output} )

Now the (regular) array looks like:

totals=( CPU0=12345 CPU1=23456 )

And you can parse it like:

for x in "${totals[@]}"; do
    name=${x%=*}
    value=${x#*=}
    echo "${name} -> ${value}"
done

(note now that splitting CPU name and value occurs in the loop).