Replace white spaces with underscores within a file (bash)

I am currently writing a script that accesses another file using “mapfile” to put it into an array. However, the inputted file contains some white spaces, which the script reads as a new array entry.

How do I replace the white spaces with underscores within the body of the file I’m bringing in? I have only seen instructions for how to replace a file name, not what’s within it.

Thank you in advance! Please let me know if you need any further clarification.

Answer

Given:

$ cat file
1 2 3 4 

You can use sed:

$ sed 's/[[:space:]]/_/g' file
1_2_3_4

So then you can do:

$ mapfile -t arr < <(sed 's/[[:space:]]/_/g' file)