eval to interpret new lines in bash

Question

I have a previously run command $cmd, this command outputs multiple lines.

I would like to take the nth line of output from running an edited version of $cmd.

So far I have tried:

local -a lines

for line in $(eval "$(some_edit $cmd)");do
  lines+=("$line")
done

echo "${lines[$nth_line]}"

I always echo everything when $nth_line is 1 and nothing for larger integers.

I always have $lines being an array of one string - which is all the lines.

I have tried combinations of ", but to no avail.

Answer 1

I don't know if i understand you correct - you mean something like that?

#!/bin/bash
cmd="./script.sh"

# read stdout from $cmd into array lines
readarray lines < <($cmd)

# edit the second line
lines[1]=$'version: 0.99\n'

# loop over array and print lines
for line in "${lines[@]}"; do
   printf "%s" "$line"
done

testscript for simulate $cmd

#!/bin/bash
echo "start"
echo
echo "do something"
echo
echo "end"

output

start
version: 0.99
do something

end