bash Sed 和美元符号
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Sed and dollar sign
提问by threaz
"The Unix Programming Environment" states that '$' used in regular expression in sed means end-of-the line which is fine for me, because
“Unix 编程环境”指出 sed 中正则表达式中使用的“$”表示行尾，这对我来说很好，因为
cat file | sed 's/$/\n/'
is interpretted as "add newline at the end of each line".
被解释为“在每行末尾添加换行符”。
The question arises, when I try to use the command:
问题出现了，当我尝试使用命令时：
cat file | sed '$d'
Shouldn't this line remove each line instead of the last one? In this context, dollar sign means end of the LAST line. What am I getting wrong?
这行不应该删除每一行而不是最后一行吗？在这种情况下，美元符号意味着最后一行的结束。我怎么了？
回答by 200_success
In the second usage, there is no regular expression. The $there is an address, meaning the last line.
在第二种用法中，没有正则表达式。该$有一个地址，这意味着最后一行。
回答by anubhava
$is treated as regex anchor when used in pattern in scommand e.g.
$当在s命令中的模式中使用时，被视为正则表达式锚点，例如
s/$/\n
However in $d, $is nota regex anchor, it is address notation that means the last lineof the input, which is deleted using the dcommand.
然而，在$d，$是未正则表达式锚，它是地址表示法装置的最后一行的输入，这是使用已删除的d命令。
Also note that catis unnecessary in your last command. It can be used as:
另请注意，这cat在您的最后一个命令中是不必要的。它可以用作：
sed '$d' file
回答by Avinash Raj
Note that regexin sed must be inside the delimiters(;,:, ~, etc) other than quotes.
需要注意的是regex在sed必须是分隔符（内;，:，~，等）比其他报价。
/regex/
ex:
前任：
sed '/foo/s/bar/bux/g' file
or
或者
~regex~
ex:
前任：
sed 's~dd~s~' file
but not 'regex'. So $in '$d'won't be considered as regex by sed. '$d'acts like an address which points out the last line.
但不是'regex'。所以$in'$d'不会被 sed 视为正则表达式。'$d'就像一个地址，指出最后一行。
