Read n lines at a time using Bash

I read the help read page, but still don't quite make sense. Don't know which option to use.

How can I read N lines at a time using Bash?

Solution 1:

With Bash≥4 you can use mapfile like so:

while mapfile -t -n 10 ary && ((${#ary[@]})); do
    printf '%s\n' "${ary[@]}"
    printf -- '--- SNIP ---\n'
done < file

That's to read 10 lines at a time.

Solution 2:

While the selected answer works, there is really no need for the separate file handle. Just using the read command on the original handle will function fine.

Here are two examples, one with a string, one with a file:

# Create a dummy file
echo -e "1\n2\n3\n4" > testfile.txt

# Loop through and read two lines at a time
while read -r ONE; do
    read -r TWO
    echo "ONE: $ONE TWO: $TWO"
done < testfile.txt

# Create a dummy variable
STR=$(echo -e "1\n2\n3\n4")

# Loop through and read two lines at a time
while read -r ONE; do
    read -r TWO
    echo "ONE: $ONE TWO: $TWO"
done <<< "$STR"

Running the above as a script would output (the same output for both loops):

ONE: 1 TWO: 2
ONE: 3 TWO: 4
ONE: 1 TWO: 2
ONE: 3 TWO: 4