sed如何替换特殊字符:单引号、大于号、等号？ - Chinaunix

原帖由 ailms 于 2007-12-13 14:51 发表

[root@mail ~]# cat a
='
'>
\n
\r
[root@mail ~]# sed "s/'>/\\\'>/" a
='
\'>
\n
\r
[root@mail ~]#

原帖由 ailms 于 2007-12-14 14:57 发表
单纯 \\'>和\\\'> 并没有区别，但你要放到整个 sed 的表达式，和前面的 " ' " 一起看啊，

加个 \ 就是为了去掉 ' 字符的 quoting 含义，变成一个普通字符

[root@mail ~]# cat a
='
'>
\n
\r
[root@mail ~]# sed "s/'>/\\\'>/" a
='
\'>
\n
\r
[root@mail ~]#

原帖由 MYSQLER 于 2007-12-14 15:58 发表
感谢ailms兄不耐其烦的指教

而送给 sed 后，应该是再一次转义为 "'>"

现在想知道的是sed本身为什么还要再转义一次？

原帖由 ailms 于 2007-12-14 16:04 发表
有问题今晚再说了，我今天的本本都重启 N 遍了

QUOTING
   Quoting is used to remove the special meaning of certain characters or
   words  to the shell.  Quoting can be used to disable special treatment
   for special characters, to prevent reserved words  from being  recog-
   nized as such, and to prevent parameter expansion.

   Each  of the metacharacters listed above under DEFINITIONS has special
   meaning to the shell and must be quoted if it is to represent  itself.

   When the command history expansion facilities are being used, the his-
   tory expansion character, usually !, must be quoted to prevent history
   expansion.

   There  are  three  quoting  mechanisms: the  escape character, single
   quotes, and double quotes.

   A non-quoted backslash (\) is the escape character.  It preserves  the
   literal value  of the next character that follows, with the exception
   of <newline>.  If a \<newline> pair appears, and the backslash is  not
   itself  quoted, the \<newline> is treated as a line continuation (that
   is, it is removed from the input stream and effectively ignored).

   Enclosing characters in single quotes preserves the literal  value  of
   each  character within the  quotes. A  single  quote may not occur
   between single quotes, even when preceded by a backslash.

   Enclosing characters in double quotes preserves the literal  value  of
   all  characters within the quotes, with the exception of $, ‘, and \.
   The characters $ and ‘ retain  their  special  meaning  within  double
   quotes.The backslash retains its special meaning only when followed
   by one of the following characters: $, ‘, ", \, or <newline>.  A dou-
   ble  quote  may be quoted within double quotes by preceding it with a
   backslash.  When command history is being used, the double  quote  may
   not be used to quote the history expansion character.

   The  special  parameters    *  and @ have special meaning when in double
   quotes (see PARAMETERS below).

   Words of the form $’string’ are treated specially.  The word  expands
   to  string,  with backslash-escaped characters replaced as specifed by
   the ANSI C standard.  Backslash escape sequences,  if present,  are
   decoded as follows:
      \a    alert (bell)
      \b    backspace
      \e    an escape character
      \f    form feed
      \n    new line
      \r    carriage return
      \t    horizontal tab
      \v    vertical tab
      \\    backslash
      \’    single 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)
      \cx a control-x character

   The  expanded  result  is single-quoted, as if the dollar sign had not
   been present.

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