# clear changed list file
# read filelist
while read file
# do replacement and make backup file just in case
sed -i.bak 's/inactiveConnectionTimeout.*/inactiveConnectionTimeout=300/' $file
# optionally, grep line out for later checking
grep inactiveConnectionTimeout $file >>changed.list
Assumes files listed with full paths, one per line, in filelist file.
As above, no need to check existing value; if its already set, it just gets re-set ... same result.