How to read the file content into a variable in one go?

Question

In Java, if you know for certain a file is very small, you can use readBytes() method to read the content in one go instead of read it line by line or using buffer.

Answer 1

Process the lines inside the loop instead of after it. If you really need the file in a variable:

var=$(<file)

Answer 2

Another alternative is to use the nice mapfile builtin:

mapfile < test.file
echo "${MAPFILE[@]}"

Answer 3

As another option, you can build an array of lines. If you're running bash 4+, you can use the mapfile builtin:

mapfile -t lines <test.file

If you want the lines to be output as well as stored you could do something like this:

mapfile -t lines < <(tee /dev/tty <test.file)

Then "${lines[0]}" will be the first line of the file, "${lines[1]}" the second, and so on. ${#lines[@]} will be the number of lines; "${lines[@]}" will be the whole array, while "${lines[*]}" will be the lines joined together with spaces into one big string.

For older versions of bash, you can build the array manually:

lines=()
while IFS= read -r line
do
  printf '%s\n' "$line"
  lines+=("$line")
done < test.file