linux shell sed単引用符、二重引用符、反引用符、斜棒、反斜棒('/)

前言:
この内容を見ると、私と同じようにめまいがして、ルールが見つからないと思います.実はshellが柔軟なためです. 
実は次の原則に従って、わけのわからない事故(髪の毛を少なくする)を避けることができます.
1)反引用符(`)を絶対に使わず、$()を断固として使う
 
2)エスケープを必要としない文字列に対しては,断固として一重引用符で囲む.(反斜棒、二重引用符、または引用符を付けない場合、特殊な変化があります)
例:
/opt/syb/test # echo\opt\tmp\| sed 's:\\:\\\\:g' opttmp
echo "\opt\tmp\"| sed 's:\\:\\\\:g' > ^C  
惊いて惊いて意外ではありませんか???!!!
推奨方法:
echo '\opt' | sed 's:\\:\\\\:g'
二重引用符も使用できます.
echo '\opt' | sed "s:\\\\:\\\\\\\\:g"
 
 
エスケープリスト:
https://www.cnblogs.com/fnlingnzb-learner/p/6839669.html 
https://www.cnblogs.com/f-ck-need-u/p/7499309.html
 
そこでsedがshellとどのように対話するかについての結論を出すことができます.

shellによって解析される必要がある場合は、引用符を付けないか、二重引用符を付けない.

shellと実行コマンドが共有する特殊文字に遭遇した場合、sedによって解析されるには、単一引用符を付けるか、二重引用符で逆斜線を付けてエスケープしなければならない.

は、引用符を付けてもかまいません.

 
まとめ:
一重引用符でも二重引用符でも.
照合置換の場合:エスケープが必要\
置換/一致に対して、使用:変換なしで区切り記号として使用
 
 
 
 
https://unix.stackexchange.com/questions/379572/escaping-both-forward-slash-and-back-slash-with-sed
 
You need to escape (with backslash  \ ) all substituted slashes  /  and all backslashes  \  separately, so:

$ echo "/tmp/test/folder1/test.txt" | sed 's/\//\\\//g'
\/tmp\/test\/folder1\/test.txt

but that's rather unreadable.
However,  sed  allows to use almost any character as a separator instead of  / , this is especially useful when one wants to substitute slash  /  itself, as in your case, so using for example semicolon  ;  as separator the command would become simpler:

echo "/tmp/test/folder1/test.txt" | sed 's;/;\\/;g'

Other cases:

If one wants to stick with slash as a separator and use double quotes then all escaped backslashes have to be escaped one more time to preserve their literal values:

echo "/tmp/test/folder1/test.txt" | sed "s/\//\\\\\//g"

if one doesn't want quotes at all then yet another backslash is needed:

echo "/tmp/test/folder1/test.txt" | sed s/\\//\\\\\\//g

 

$ sed 's:/:\\/:g'  <<

https://unix.stackexchange.com/questions/398646/why-is-a-single-backslash-shown-when-using-quotes.
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. 
 
5
 
Backslash is interpreted differently according context:

Within double quotes (your first example):

The backslash  retains its special meaning  only when followed
by one of the following characters: $, `, ", \, or .

Without quotes (your second example):

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

Using the construct  $'....' , where you can use inside the quote the standard backspace character, nearly as in C. e.g. 
,  \t , etc.

Using backquotes:

When  the old-style  backquote form  of substitution  is used,
backslash retains its literal  meaning except when followed by
$, `, or \.