echo \z 和 echo "\z" 区别

xiaoqiang_linux

bash版本
4.3.11
考虑好久了，还是有的迷惑，麻烦大侠帮帮忙

echo \z       #z
echo "\z"      #\z

为什么第二行中的\没有生效

在弱引用中，转义还是有用的，比如
A=123
echo "\$A"

再比如
A=123
echo "\"A\" = $A"

xiaoqiang_linux

再补充一下：
echo有个-e参数，是使能\，使其生效
但是
echo -e “\z”
输出仍然是 \z

关阴月飞

回复 2# xiaoqiang_linux


    你的问题是什么？

xiaoqiang_linux

回复 3# 关阴月飞

echo \z
echo "\z"
为何输出不同，不是很理解
   

reyleon

不带引号, 都会进行转义

带引号, 只有当\后面的字符是元字符时才会转义

reyleon

1. 3.1.2.1 Escape Character
   
2. 
   
3. A non-quoted backslash ‘\’ is the Bash 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 itself is not quoted, the \newline is treated as a line continuation (that is, it is removed from the input stream and effectively ignored).

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1. 3.1.2.2 Single Quotes
   
2. 
   
3. 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.

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1. 3.1.2.3 Double Quotes
   
2. 
   
3. Enclosing characters in double quotes (‘"’) preserves the literal value of all characters within the quotes, with the exception of ‘$’, ‘`’, ‘\’, and, when history expansion is enabled, ‘!’. The characters ‘$’ and ‘`’ retain their special meaning within double quotes (see Shell Expansions). The backslash retains its special meaning only when followed by one of the following characters: ‘$’, ‘`’, ‘"’, ‘\’, or newline. Within double quotes, backslashes that are followed by one of these characters are removed. Backslashes preceding characters without a special meaning are left unmodified. A double quote may be quoted within double quotes by preceding it with a backslash. If enabled, history expansion will be performed unless an ‘!’ appearing in double quotes is escaped using a backslash. The backslash preceding the ‘!’ is not removed.
   
4. 
   
5. The special parameters ‘*’ and ‘@’ have special meaning when in double quotes (see Shell Parameter Expansion).

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http://www.gnu.org/software/bash/manual/bash.html#Escape-Character

xiaoqiang_linux

回复 5# reyleon

大侠，感想你的回复

我看了下，你提供bash手册的描述，我的理解是：
在弱引用("")中，只有反斜杠后面跟着元字符（meta字符，特殊字符）
这些元字符仅仅包括
$
`             #反引号
"             #双引号
\             #反斜杠
newline    #换行符
！             #前提是历史机制被使能

在弱引用中，这些字符的特殊含义被才会取消，变成普通字符，否则就采用其特殊字符含义




   

reyleon

回复 7# xiaoqiang_linux


  意思就是你明白了咯