Access 'cat' output as an array in 'bash'

Question

I am trying to access some numeric values that a regular 'cat' outputs in an array.

If I do: cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_available_frequencies

I get: 51000 102000 204000 312000 ...

So I scripted as below to get all elements in an array and I tried to get the number of elements.

vAvailableFrequencies=$(sudo cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_available_frequencies)
nAvailableFrequencies=${#vAvailableFrequencies[@]}

The problem is that nAvailableFrequencies is equal to the number of characters in the array, not the number of elements.

The idea is to be able to access each element as:

for (( i=0;i<$nAvailableFrequencies;i++)); do
   element=${vAvailableFrequencies[$i]
done

Is this possible in bash without doing something like a sequential read and inserting elements in the array one by one?

anubhava · Accepted Answer · 2015-08-18 13:53:45Z

3

You can use array like this:

arr=($(</sys/devices/system/cpu/cpu0/cpufreq/scaling_available_frequencies))

nAvailableFrequencies=${#arrr}

$(<file) reads and outputs a file content while (...) creates an array.

edited Aug 18, 2015 at 13:53

answered Aug 18, 2015 at 12:08

anubhava

790k67 gold badges603 silver badges671 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

arco444 · Accepted Answer · 2015-08-18 12:06:25Z

1

You just need another set of brackets around the vAvailableFrequencies assignment:

vAvailableFrequencies=($(cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_available_frequencies))
nAvailableFrequencies=${#vAvailableFrequencies[@]}

Now you can access within your for loop, or individually with ${vAvailableFrequencies[i]} where i is the number of an element

answered Aug 18, 2015 at 12:06

arco444

23k12 gold badges66 silver badges67 bronze badges

Comments

chepner · Accepted Answer · 2015-08-18 13:14:27Z

1

If you are using bash 4 or later, use

readfile -t vAvailableFrequencies < /sys/devices/system/cpu/cpu0/cpufreq/scaling_available_frequencies

(or, if you need to use sudo,

readfile -t vAvailableFrequencies < <(sudo cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_available_frequencies)

)

answered Aug 18, 2015 at 13:14

chepner

538k77 gold badges594 silver badges747 bronze badges

Collectives™ on Stack Overflow

Access 'cat' output as an array in 'bash'

3 Answers 3

Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related