shell中$后加引号有什么用($string和$'string')

bash&shell系列文章：http://www.cnblogs.com/f-ck-need-u/p/7048359.html

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有些时候在某些服务管理脚本中看到$"$string"或$"string"，经过一些测试，又发现引号外面的$有和没有是一样的。一直也没去找究竟，刚才有人问了我，于是就去翻了下man bash，找到了解释。

(1).如果没有特殊定制bash环境或有特殊需求，$"string"和"string"是完全等价的，使用$""只是为了保证本地化。

以下是man bash关于$""的解释：

A double-quoted string preceded by a dollar sign ($"string") will cause the string to be translated according to the current locale. Ifthe current locale is C or POSIX, the dollar sign is ignored. If the string is translated and replaced, the replacement is double-quoted.

(2).还有$后接单引号的$'string'，这在bash中被特殊对待：会将某些反斜线序列(如\n，\t，\"，\'等)继续转义，而不认为它是字面符号(如果没有$符号，单引号会强制将string翻译为字面符号，包括反斜线)。简单的例子：

[root@xuexi ~]# echo 'a\nb' a\nb [root@xuexi ~]# echo $'a\nb' a b

以下是man bash里关于$'的说明：

Words of the form $'string' are treated specially. The word expands to string, with backslash-escaped characters replaced as specified by the ANSI C standard. Backslash escape sequences, if present, are decoded as follows:\a alert (bell)\b backspace\e\E an escape character\f form feed\n new line\r carriage return\t horizontal tab\v vertical tab\\ backslash\' single quote\" double quote\nnn the eight-bit character whose value is the octal value nnn (one to three digits)\xHH the eight-bit character whose value is the hexadecimal value HH (one or two hex digits)\uHHHH the Unicode (ISO/IEC 10646) character whose value is the hexadecimal value HHHH (one to four hex digits)\UHHHHHHHHthe Unicode (ISO/IEC 10646) character whose value is the hexadecimal value HHHHHHHH (one to eight hex digits)\cx a control-x character

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