Why doesn't `"hello\r".chomp('')` remove `"\r"`?

Question

Although the Ruby reference manual describes:

If $/ is an empty string, it will remove all trailing newlines from the string.

"hello\r".chomp('') doesn't remove "\r" as in the following.

"hello\r\n".chomp     # => "hello"
"hello\r".chomp       # => "hello"
"hello\r\n".chomp('') # => "hello"
"hello\r".chomp('')   # => "hello\r"

Why?

Answer 1

If $/ is an empty string, it will remove all trailing newlines from the string.

Exactly. \r AKA CR is not a newline character. It's a carriage return character (doesn't start a new line).

As to why chomp('') removes CRLF, it's because CRLF is a Windows-style newline. Linux uses LF.

Old Mac OSes (up to v9) were using CR, but recent ones (OS X) do not. So "CR as a newline char" does not exist as far as ruby is concerned.

Answer 2

The short explanation is that \r is not a newline, but a carriage return. So chomp() does exactly what the manual states.

The long explanation can be found on the Control_character Wikipedia page.