how can i update the variable during application working

Hi, I create a command line action and this action create random number and write into the a.txt file. After that I can catch this random number in a.txt file with variable manager(file variable). when I run project I need this variable to use at the next action. The problem is How can I update the variable during project running. I tried varible modify but it did not work. it uptade after end of project check. Do you any suggestion? Thanks a lot.