如何找到连续的空白行并将其转换为一条 [英] how to find continuous blank lines and convert them to one
问题描述
我有一个文件-a，并且存在一些连续的空行(不止一个)，请参见下文:
cat a
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所以首先我想知道是否存在继续空白行，我尝试过
cat a | grep '\n\n\n'
没有任何输出.所以我必须使用下面的方式
vi a
:set list
/\n\n\n
所以我想知道是否存在其他shell命令可以轻松实现这一点? 那么如果存在两个和更多的空白行，我想将它们转换为一个?见下文
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起初我尝试在shell之下
sed 's/\n\n\(\n\)*/\n\n/g' a
它不起作用，然后我尝试了这个shell
cat a | tr '\n' '$' | sed 's/$$\(\$\)*/$$/g' | tr '$' '\n'
这一次有效.而且我还想知道是否存在其他方式可以实现这一目标?
如果您的cat实现支持
-s, --squeeze-blank
suppress repeated empty output lines
那么就这么简单
$ cat -s a
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此外，-s和-n都可以通过less命令使用.
备注:仅包含空格的行将不会被取消.
如果您的cat不支持-s，则可以使用:
awk 'NF||p; {p=NF}'
或者如果您想保证每条记录之后都包含空白行，包括输出末尾，即使输入中不存在空白行，那么:
awk -v RS= -v ORS='\n\n' '1'
如果您的输入包含所有空白行，并且希望将它们像非空白行一样对待(如cat -s一样，请参见下面的注释)，然后:
awk '/./||p; {p=/./}'
并确保输出末尾有空白行:
awk '/./||p; {p=/./} END{if (p) print ""}'
I have a file -- a, and exist some continues blank line(more than one), see below:
cat a
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So first I want to know if exist continues blank lines, I tried
cat a | grep '\n\n\n'
nothing output. So I have to use below manner
vi a
:set list
/\n\n\n
So I want to know if exist other shell command could easily implement this? then if exist two and more blank lines I want to convert them to one? see below
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at first I tried below shell
sed 's/\n\n\(\n\)*/\n\n/g' a
it does not work, then I tried this shell
cat a | tr '\n' '$' | sed 's/$$\(\$\)*/$$/g' | tr '$' '\n'
this time it works. And also I want to know if exist other manner could implement this?
Well, if your cat implementation supports
-s, --squeeze-blank
suppress repeated empty output lines
then it is as simple as
$ cat -s a
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Also, both -s and -n for numbering lines is likely to be available with less command as well.
remark: lines containing only blanks will not be suppressed.
If your cat does not support -s then you could use:
awk 'NF||p; {p=NF}'
or if you want to guarantee a blank line after every record, including at the end of the output even if none was present in the input, then:
awk -v RS= -v ORS='\n\n' '1'
If your input contains lines of all white space and you want them to be treated just like lines of non white space (like cat -s does, see the comments below) then:
awk '/./||p; {p=/./}'
and to guarantee a blank line at the end of the output:
awk '/./||p; {p=/./} END{if (p) print ""}'
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