echo要支持同C语言一样的\转义功能，只需要加上参数-e，如下所示：
[~]#echo "Hello world.\nHello sea"
Hello world.\nHello sea
[~]#echo -e "Hello world.\nHello sea"
Hello world.
Hello sea
[~]#
不加-e
看一下man的说明：
[~]#man echo | cat
ECHO(1) User Commands ECHO(1)
NAME
echo - display a line of text
SYNOPSIS
echo [OPTION]... [STRING]...
DESCRIPTION
Echo the STRING(s) to standard output.
-n do not output the trailing newline
-e enable interpretation of backslash escapes
-E disable interpretation of backslash escapes (default)
--help display this help and exit
--version
output version information and exit
If -e is in effect, the following sequences are recognized:
\0NNN the character whose ASCII code is NNN (octal)
\\ backslash
\a alert (BEL)
\b backspace
\c suppress trailing newline
\f form feed
\n new line
\r carriage return
\t horizontal tab
\v vertical tab
NOTE: your shell may have its own version of echo, which usually super-
sedes the version described here. Please refer to your shell’s docu-
mentation for details about the options it supports.