How to replace a value with the output of a command in a text file?

Question

I have a file that contains:

I want to replace in bash, the value 0

Answer 1

In general, do use this syntax:

sed "s//$(command)/" file

This will look for and replace it with the output of command.

---

For your specific problem, you can use the following:

sed "s/0/$(date +%s)/g" input.txt > output.txt

This replaces any 0 present in the file with the output of the command date +%s. Note you need to use double quotes to make the command in $() be interpreted. Otherwise, you would get a literal $(date +%s).

If you want the file to be updated automatically, add -i to the sed command: sed -i "s/.... This is called in-place editing.

---

Test

Given a file with this content:

Let's see what it returns:

$ sed "s/0/$(date +%s)/g" file