Interview › Scripting (Bash, Groovy)
What is the correct way to read a file line by line, and why not use for line in $(cat)? [Basic]
Answer
The correct pattern is while IFS= read -r line; do ... done < file. Do not use for line in $(cat file) because command substitution performs word splitting, removes important whitespace, and can break lines into words instead of records.
Technical explanation
IFS= preserves leading and trailing whitespace while reading.
read -r prevents backslashes from being treated as escapes.
Redirecting the file into the loop avoids unnecessary cat and handles lines predictably.
Hands-on example
while IFS= read -r line || [[ -n "$line" ]]; do
printf 'line=[%s]\n' "$line"
done < input.txt
# Bad: for line in $(cat input.txt); do ...; done
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