how to read line by line from file in bash script?

Like this?

while IFS= read line ; do   something "$line"done <"$file"

Here is a brief test:

while IFS= read line ; do echo "$line"; done <<<"$(echo -e "a b\nc d")"a bc d

file bash scripting line

You can you readarray (bash 4+)

readarray lines < "$file"

then

for line in "${lines[@]}"; do    echo "$line"done

Note that by default readarray will even include the line-end character for each line

CodeHunter