Question

If the following example, which sets the IFS environment variable to a line feed character…

IFS=$'\n'

• What does the dollar sign mean
  exactly?
• What does it do in this specific
  case?
• Where can I read more on this specific usage (Google doesn’t allow special characters in searches and I don’t know what to look for otherwise)?

I know what the IFS environment variable is, and what the \n character is (line feed), but why not just use the following form:
IFS="\n" (which does not work)?

For example, if I want to loop through every line of a file and want to use a for loop, I could do this:

for line in (< /path/to/file); do
    echo "Line: $line"
done

However, this won’t work right unless IFS is set to a line feed character. To get it to work, I’d have to do this:

OLDIFS=$IFS
IFS=$'\n'
for line in (< /path/to/file); do
    echo "Line: $line"
done
IFS=$OLDIFS

Note: I don’t need another way for doing the same thing, I know many other already… I’m only curious about that $'\n' and wondered if anyone could give me an explanation on it.

Answer 1

Normally bash doesn’t interpret escape sequences in string literals. So if you write \n or "\n" or '\n', that’s not a linebreak – it’s the letter n (in the first case) or a backslash followed by the letter n (in the other two cases).

$'somestring' is a syntax for string literals with escape sequences. So unlike '\n', $'\n' actually is a linebreak.