Read n lines at a time using Bash

Question

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?

Answer 1

After having looked at all the answers, I think the following is the simplest, ie more scripters would understand it better than any other solution, but only for small number of items:

while read -r var1 && read -r var2; do 
    echo "$var1" "$var2"
done < yourfile.txt

The multi-command approach is also excellent, but it is lesser known syntax, although still intuitive:

while read -r var1; read -r var2; do 
    echo "$var1" "$var2"
done < yourfile.txt

It has the advantage that you don't need line continuations for larger number of items:

while 
    read -r var1
    read -r var2
    ...
    read -r varN
do 
    echo "$var1" "$var2"
done < yourfile.txt

The xargs answer posted is also nice in theory, but in practice processing the combined lines is not so obvious. For example one solution I came up with using this technique is:

while read -r var1 var2; do 
    echo "$var1" "$var2"
done <<< $(cat yourfile.txt | xargs -L 2 )

but again this uses the lesser known <<< operator. However this approach has the advantage that if your script was initially

while read -r var1; do 
    echo "$var1"
done <<< yourfile.txt

then extending it for multiple lines is somewhat natural:

while read -r var1 var2; do 
    echo "$var1" "$var2"
done <<< $(cat endpoints.txt | xargs -L 2 )

The straightforward solution

while read -r var1; do
    read -r var2
    echo "$var1" "$var2"
done < yourfile.txt

is the only other one that I would consider among the many given, for its simplicity, but syntactically it is not as expressive; compared to the && version or multi-command version it does not feel as right.