how i can read file and store its containt in variable?

Question

i want to store number in file for example file number.txt contain 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

Answer 1

number_var=$(cat number.txt)

Answer 2

The backtick is your friend:

[madhatta@risby tmp]$ cat foo
1234
[madhatta@risby tmp]$ fred=`cat foo`
[madhatta@risby tmp]$ echo $fred
1234

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!

Answer 3

In Bash, ksh and zsh:

number_var=$(<number.txt)