I want to store number in file for example file
3242 I want to real this file and store its contant in variable for example variable
number_var = number.txt so that
number_var = 3242
The backtick is your friend:
You had better be pretty sure the file is a one-liner, though; if you import the whole of /boot/vmlinuz into a shell variable, you may start putting pressure on memory!