This is not working. It is printing all XML

Code:

sed -r 's/.*initialHeapSize[^0-9]*=[^0-9]*([0-9]+).*/\1/' server.xml

below two solutions are working.

Code:

grep -Eo 'initialHeapSize[^0-9]*=[^0-9]*[0-9]+' | sed 's/.*[^0-9]//' server.xml
grep -Po 'initialHeapSize\D*=\D*\d+' | sed 's/.*[^0-9]//'  server.xml

But I think using initialHeapSize[^0-9]*= could select any text preceding =.
Better way to do it is to say there can be spaces between key and =. There can be zero or more spaces after = and a single or double quote followed by digits.

Code:

cat server.xml | grep '<jvmEntries' | grep -iEo 'initialHeapSize[[:space:]]*=[[:space:]]*[\x27"]?[0-9]+'  | sed 's/.*[^0-9]//'
256

If I can use above regex in a single sed statement that would even better to understand and maintain.

I think this also is a great solution, if only I could push grep condition into perl regex. This is case insensitive and tries to be precise with key=value matching with best guess for space, =, quotes

Code:

cat server.xml | grep -i '<jvmEntries' |  perl -ne 'print /initialheapSize[[:space:]]*=[[:space:]]*[\x27"]?(\d+)/i'