I don't use bash often but I recall in the past to pass a tab or newline on the command line I would have to escape the character using the special $ character before a single quoted string. Like $'\t', $'\n', etc. I had read about quotes and escaping in the bash manual.

What I want to know is when it's appropriate to use an ANSI C style escape. For example I was working with a regex in grep and it appeared I needed an ANSI C style escape for a newline. Then I switched to perl and it seemed I didn't.

Take for example my recent question on stackoverflow about a perl regex that didn't work. Here's the regex I was using:

echo -e -n "ab\r\ncd" | perl -w -e $'binmode STDIN;undef $/;$_ = <>;if(/ab\r\ncd/){print "test"}'

It turns out that is actually incorrect because I gave the string ANSI C style escape by using $. I just don't understand when I'm supposed to prepend the dollar sign and when I'm not.

Thanks