A string is written between double-quotes. It may contain double-quotes or null characters. The way to get special characters into a string is to escape these characters: precede them with a backslash ‘\’ character. For example ‘\\’ represents one backslash: the first
\ is an escape which tells
as to interpret the second character literally as a backslash (which prevents
as from recognizing the second
\ as an escape character). The complete list of escapes follows.
Mnemonic for backspace; for ASCII this is octal code 010.
Mnemonic for FormFeed; for ASCII this is octal code 014.
Mnemonic for newline; for ASCII this is octal code 012.
Mnemonic for carriage-Return; for ASCII this is octal code 015.
Mnemonic for horizontal Tab; for ASCII this is octal code 011.
An octal character code. The numeric code is 3 octal digits. For compatibility with other Unix systems, 8 and 9 are accepted as digits: for example,
\008 has the value 010, and
\009 the value 011.
A hex character code. All trailing hex digits are combined. Either upper or lower case
Represents one ‘\’ character.
Represents one ‘"’ character. Needed in strings to represent this character, because an unescaped ‘"’ would end the string.
Any other character when escaped by \ gives a warning, but assembles as if the ‘\’ was not present. The idea is that if you used an escape sequence you clearly didn’t want the literal interpretation of the following character. However
as has no other interpretation, so
as knows it is giving you the wrong code and warns you of the fact.
Which characters are escapable, and what those escapes represent, varies widely among assemblers. The current set is what we think the BSD 4.2 assembler recognizes, and is a subset of what most C compilers recognize. If you are in doubt, do not use an escape sequence.