echo \z 和 echo "\z" 區(qū)別

xiaoqiang_linux

bash版本
4.3.11
考慮好久了，還是有的迷惑，麻煩大俠幫幫忙

echo \z       #z
echo "\z"      #\z

為什么第二行中的\沒有生效

在弱引用中，轉義還是有用的，比如
A=123
echo "\$A"

再比如
A=123
echo "\"A\" = $A"

xiaoqiang_linux

再補充一下：
echo有個-e參數(shù)，是使能\，使其生效
但是
echo -e “\z”
輸出仍然是 \z

關陰月飛

回復 2# xiaoqiang_linux


    你的問題是什么？

xiaoqiang_linux

回復 3# 關陰月飛

echo \z
echo "\z"
為何輸出不同，不是很理解
   

reyleon

不帶引號, 都會進行轉義

帶引號, 只有當\后面的字符是元字符時才會轉義

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).

復制代碼

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.

復制代碼

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).

復制代碼

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

xiaoqiang_linux

回復 5# reyleon

大俠，感想你的回復

我看了下，你提供bash手冊的描述，我的理解是：
在弱引用("")中，只有反斜杠后面跟著元字符（meta字符，特殊字符）
這些元字符僅僅包括
$
`             #反引號
"             #雙引號
\             #反斜杠
newline    #換行符
！             #前提是歷史機制被使能

在弱引用中，這些字符的特殊含義被才會取消，變成普通字符，否則就采用其特殊字符含義




   

reyleon

回復 7# xiaoqiang_linux


  意思就是你明白了咯