☰

带或不带十六进制双引号的 ECHO 行为

tag-icon • tag-icon bash echo
带或不带十六进制双引号的 ECHO 行为

有人能帮助我理解的行为echo吗？我在 Ubuntu 中尝试以下命令：

$ echo -e \xaa
xaa
$ echo -e "\xaa"

▒
$

如您所见，使用双引号时，在打印十六进制时，输出是一些垃圾。我知道-e解释\n为换行符和其他序列很有用。我只是想了解带-e选项的 echo 如何处理十六进制。

答案1

如果没有引号，\x则 shell 会将其解析为x：

$ printf "%s\n" echo -e \xaa
echo
-e
xaa    
$ printf "%s\n" echo -e "\xaa"
echo
-e
\xaa

看man bash， 部分QUOTING：

   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).

你的grep说法具有误导性：

$ man echo | grep -o \xHH
xHH

grep -o准确打印匹配的字符，表明grep从未收到\。

除非您运行/bin/echo或env echo，否则将运行 shell 的内置命令echo。因此，如果您想查看文档，请运行help echo，或者查看man bash。man echo适用于/bin/echo：

$ echo --help
--help
$ env echo --help
Usage: echo [SHORT-OPTION]... [STRING]...
  or:  echo LONG-OPTION
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 recognised:

  \\      backslash
...

请参阅man bash第节SHELL BUITLIN COMMANDS：

  echo interprets the following escape sequences:
  \a     alert (bell)
  \b     backspace
  \c     suppress further output
  \e
  \E     an escape character
  \f     form feed
  \n     new line
  \r     carriage return
  \t     horizontal tab
  \v     vertical tab
  \\     backslash
  \0nnn  the eight-bit character whose value is  the  octal  value
         nnn (zero to three octal digits)
  \xHH   the  eight-bit  character  whose value is the hexadecimal
         value HH (one or two hex digits)

相关内容