The echo command is as specified in POSIX 1003.1-2001 (ISO/IEC 9945-2003), but with the following differences.
Implementations may support implementation-defined options to echo. The behavior of echo if any arguments contain backslashes is also implementation defined.
Conforming applications should not run echo with a first argument starting with a hyphen, or with any arguments containing backslashes; they should use printf in those cases.
Note: The behavior specified here is similar to that specified by POSIX 1003.1-2001 (ISO/IEC 9945-2003) without the XSI option. However, the LSB strongly recommends conforming applications not use any options (even if the implementation provides them) while POSIX 1003.1-2001 (ISO/IEC 9945-2003) specifies behavior if the first operand is the string -n.