Write a bash shell script that consumes a constant amount of RAM for a user defined time

Question

I am trying to write a bash shell script that consumes a high amount of RAM on an embedded device for a user defined time. How do I do it without using arrays ?

Answer 1

Even if traditional Bash arrays are not supported, it may still be possible to create array-like variables using the eval command built into the particular shell.

The following example script is based on some scripting I did when using BusyBox in an embedded Linux project. BusyBox uses the Almquist shell (also known as A Shell, ash, and sh), which does not support arrays.

#!/bin/ash

for index in 1 2 3 4 5; do
    value=$(($index * 1024))
    eval array$index=\"array[$index]: $value\"
done

for i in 1 3 5; do
    eval echo \$array$i
done

_{Be careful with quoting when using eval!}

Output:

array[1]: 1024
array[3]: 3072
array[5]: 5120

---

Depending on your particular scenario, a script similar to the following may suffice.

#!/bin/ash

echo "Provide sleep time in the form of NUMBER[SUFFIX]"
echo "   SUFFIX may be 's' for seconds (default), 'm' for minutes,"
echo "   'h' for hours, or 'd' for days."
read -p "> " delay

echo "begin allocating memory..."
for index in $(seq 1000); do
    value=$(seq -w -s '' $index $(($index + 100000)))
    eval array$index=$value
done
echo "...end allocating memory"

echo "sleeping for $delay"
sleep $delay

In my brief testing, this script consumed ~570M to ~575M physical memory^* for the specified time period of 5 minutes.

^{* Monitored using top and memprof programs in separate tests}