如果使用 sed 和带有扩展语法的正则表达式的特定模式的一部分，则用新行替换空格

Question

so I have a text file with multiple instances looking like this:

word. word or words [something:'else]

I need to replace with a new line the double space after every period followed by a sequence of words and then a "[", like so:

word.\nword or words [something:'else]

I thought about using the sed command in bash with extended regex syntax, but nothing has worked so far... I've tried different variations of this:

sed -E 's/(\.)( )(.*)(.\[)/\1\n\3\4/g' old.txt > new.txt

I'm an absolute beginner at this, so I'm not sure at all about what I'm doing

Answer 1

This might work for you (GNU sed):

sed -E 's/\.  ((\w+ )+\[)/\.\n\1/g' file

Replace globally a period followed by two spaces and one or more words space separated followed by an opening square bracket by; a period followed by a newline followed by the matching back reference from the regexp.

Answer 2

Your sed command is almost correct (but contains some redundancies)

sed -E 's/(\.)(  )(.*)(.\[)/\1\n\3\4/' old.txt > new.txt
#                                   ^
#                                   You forget terminating the s command

But you don't need to capture everything. A simpler one could be

sed -E 's/\.  (.*\[)/.\n\1/' old.txt > new.txt