How to read variables from file, with multiple var

Question

I'm trying to read from a file, that has multiple lines, each with 3 informations I want to assign to the variables and work with.

I figured out, how to simply display them each on the terminal, but can't figure out how to actually assign them to variables.

while read i
do
  for j in $i
  do
    echo $j
  done
done < ./test.txt

test.txt:

1 2 3
a b c

So I want to read the line in the outer loop, then assign the 3 variables and then work with them, before going to the next line.

I'm guessing I have to read the values of the lines without an inside loop, but I can't figure it out right now.

Hope someone can point me in the right direction.

Answer 1

I think all you're looking for is to read multiple variables per line: the read command can assign words to variables by itself.

while read -r first second third; do
    do_stuff_with "$first"
    do_stuff_with "$second"
    do_stuff_with "$third"
done < ./test.txt

Answer 2

The below assumes that your desired result is the set of assignments a=1, b=2, and c=3, taking the values from the first line and the keys from the second.

---

The easy way to do this is to read your keys and values into two separate arrays. Then you can iterate only once, referring to the items at each position within those arrays.

#!/usr/bin/env bash
case $BASH_VERSION in
  ''|[123].*) echo "ERROR: This script requires bash 4.0 or newer" >&2; exit 1;;
esac

input_file=${1:-test.txt}

# create an associative array in which to store your variables read from a file
declare -A vars=( )

{
  read -r -a vals               # read first line into array "vals"
  read -r -a keys               # read second line into array "keys"
  for idx in "${!keys[@]}"; do  # iterate over array indexes (starting at 0)
    key=${keys[$idx]}           # extract key at that index
    val=${vals[$idx]}           # extract value at that index
    vars[$key]=$val             # assign the value to the key inside the associative array
  done
} < "$input_file"

# print for debugging
declare -p vars >&2

echo "Value of variable a is ${vars[a]}"

See:

• BashFAQ #6 - How can I use variable variables (indirect variables, pointers, references) or associative arrays?
• The bash-hackers page on the read builtin, documenting use of -a to read words into an array.