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..
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.
${var%.*} removes a dot and anything following it at the end of the string.
# means "remove from the left", and * is just a wildcard that matches everything.
${var//[A-Z,a-z,:]}Other possible solutions:
With grep:
var="Memory Used: 19.54M"
var=`echo "$var" | grep -o "[0-9.]\+"`
With sed:
var="Memory Used: 19.54M"
var=`echo "$var" | sed 's/.*\ \([0-9\.]\+\).*/\1/g'`
With cut:
var="Memory Used: 19.54M"
var=`echo "$var" | cut -d ' ' -f 3 | cut -d 'M' -f 1`
With awk:
var="Memory Used: 19.54M"
var=`echo "$var" | awk -F'[M ]' '{print $4}'`
You can use bash regex support with the =~ operator, as follows:
var="Memory Used: 19.54M"
if [[ $var =~ Memory\ Used:\ (.+)M ]]; then
echo ${BASH_REMATCH[1]}
fi
This will print 19.54
> echo "Memory Used: 19.54M" | perl -pe 's/\d+\.\d+//g'
Memory Used: M
