for i in CPU*; do num=$(echo "$i" | cut -c4 -); cp file.txt $i; sed -i "s/something/$num/g" $i/file.txt; done
[root@herlo-lap ~]# vi file.txt 
[root@herlo-lap ~]# for i in CPU*; do cat $i/file.txt; done
item=1
item=3
item=4
item=5
item=6