在shell命令行中将两个换行符替换为一个 [英] replace two newlines to one in shell command line

问题描述

关于将多个换行符替换为一个换行符存在很多问题，但是没有人为我工作.
我有一个文件:

There are lot of questions about replacing multi-newlines to one newline but no one is working for me.
I have a file:

first line
second line MARKER

third line MARKER
other lines

many other lines

我需要将MARKER之后的两个换行符替换为一个换行符.结果文件应为:

I need to replace two newlines (if they exist) after MARKER to one newline. A result file should be:

first line
second line MARKER
third line MARKER
other lines

many other lines

我尝试了sed ':a;N;$!ba;s/MARKER\n\n/MARKER\n/g'失败.
sed对于单行替换很有用，但换行符有问题.找不到\n\n

I tried sed ':a;N;$!ba;s/MARKER\n\n/MARKER\n/g' Fail.
sed is useful for single line replacements but has problems with newlines. It can't find \n\n

我尝试了perl -i -p -e 's/MARKER\n\n/MARKER\n/g'失败.
这个解决方案看起来更近了，但是似乎regexp对\n\n没有反应.

I tried perl -i -p -e 's/MARKER\n\n/MARKER\n/g' Fail.
This solution looks closer, but it seems that regexp didn't reacts to \n\n.

是否可以仅在MARKER之后替换\n\n而不能替换文件中的其他\n\n?
我对单行解决方案感兴趣，而不是脚本.

Is it possible to replace \n\n only after MARKER and not to replace other \n\n in the file?
I am interested in one-line-solution, not scripts.

推荐答案

我认为您的做法正确.在多行程序中，您会将整个文件加载到单个标量中，然后在其上运行此替换:

I think you were on the right track. In a multi-line program, you would load the entire file into a single scalar and run this substitution on it:

s/MARKER\n\n/MARKER\n/g

使单线加载文件到多行字符串的诀窍是在BEGIN块中设置$/.在读取输入之前，该代码将执行一次.

The trick to getting a one-liner to load a file into a multi-line string is to set $/ in a BEGIN block. This code will get executed once, before the input is read.

perl -i -pe 'BEGIN{$/=undef} s/MARKER\n\n/MARKER\n/g' input

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