vi里的\n,为什么在sed里不认那

dida_327

vi里
:%s/\n//g  可以
但是
sed '/\n//g file > result
就是不行

Edengundam

\n 在用 sed 处理时候, 压根儿没有出现在 pattern space ...所以匹配不到.
但是用 N 命令时候 pattern space 会出现 \n 这时候就匹配了

i_amok

因为sed会去掉每个输入行的结尾的回车,具体参见下面的文章

5.10. Why can't I match or delete a newline using the \n escape sequence?
Why can't I match 2 or more lines using \n?

The \n will never match the newline at the end-of-line because the
newline is always stripped off before the line is placed into the
pattern space. To get 2 or more lines into the pattern space, use
the 'N' command or something similar (such as 'H;...;g;').

Sed works like this: sed reads one line at a time, chops off the
terminating newline, puts what is left into the pattern space where
the sed script can address or change it, and when the pattern space
is printed, appends a newline to stdout (or to a file). If the
pattern space is entirely or partially deleted with 'd' or 'D', the
newline is *not* added in such cases. Thus, scripts like

sed 's/\n//' file # to delete newlines from each line
sed 's/\n/foo\n/' file # to add a word to the end of each line

will _never_ work, because the trailing newline is removed _before_
the line is put into the pattern space. To perform the above tasks,
use one of these scripts instead:

tr -d '\n' < file # use tr to delete newlines
sed ':a;N;$!ba;s/\n//g' file # GNU sed to delete newlines
sed 's/$/ foo/' file # add "foo" to end of each line

Since versions of sed other than GNU sed have limits to the size of
the pattern buffer, the Unix 'tr' utility is to be preferred here.
If the last line of the file contains a newline, GNU sed will add
that newline to the output but delete all others, whereas tr will
delete all newlines.

To match a block of two or more lines, there are 3 basic choices:
(1) use the 'N' command to add the Next line to the pattern space;
(2) use the 'H' command at least twice to append the current line
to the Hold space, and then retrieve the lines from the hold space
with x, g, or G; or (3) use address ranges (see section 3.3, above)
to match lines between two specified addresses.

Choices (1) and (2) will put an \n into the pattern space, where it
can be addressed as desired ('s/ABC\nXYZ/alphabet/g'). One example
of using 'N' to delete a block of lines appears in section 4.13
("How do I delete a block of _specific_ consecutive lines?"). This
example can be modified by changing the delete command to something
else, like 'p' (print), 'i' (insert), 'c' (change), 'a' (append),
or 's' (substitute).

Choice (3) will not put an \n into the pattern space, but it _does_
match a block of consecutive lines, so it may be that you don't
even need the \n to find what you're looking for. Since several
versions of sed support this syntax:

sed '/start/,+4d' # to delete "start" plus the next 4 lines,

in addition to the traditional '/from here/,/to there/{...}' range
addresses, it may be possible to avoid the use of \n entirely.

不过这个pattern space 有大小的限制，如果文件很大，用tr来做替换工作是首选。