Question

Say I have the string “Memory Used: 19.54M”
How would I extract the 19.54 from it?
The 19.54 will change frequently so i need to store it in a variable and compare it with the value on the next iteration.

I imagine I need some combination of grep and regex, but I never really understood regex..

Answer 1

You probably want to extract it rather than remove it. You can use the Parameter Expansion to extract the value:

var="Memory Used: 19.54M"
var=${var#*: }            # Remove everything up to a colon and space
var=${var%M}              # Remove the M at the end

Note that bash can only compare integers, it has no floating point arithmetics support.