CODEWITHSUNDEEP
arrayslinuxbashshellscripting
VAndrei
VAndrei

Reputation: 5570

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

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?

Upvotes: 1

Views: 2996

Answers (3)

anubhava
anubhava

Reputation: 785008

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.

Upvotes: 3

chepner
chepner

Reputation: 530990

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)

)

Upvotes: 1

arco444
arco444

Reputation: 22821

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

Upvotes: 1

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