Question

I have a text file like

Hi
how are you
<blank>
<blank>
abcd
<blank>
defgh
opqr
<blank>

I want to print all lines that have the pattern like “some text”blankblank”some text”
like

how are you
<blank>
<blank>
abcd

I am thinking about using join and then search for the pattern. But I am not sure how to do it. (By blank I mean empty line)

Answer 1

• Blank line: /^(?:(?!\n)\s)*\n/m
• Non-blank line: /^.*\S.*\n/m

So you want to print all instances of:

 /
    ^
    (?:
       .*\S.*\n
       (?: (?:(?!\n)\s)*\n ){2}
    )+
    .*\S.*\n
 /mx

As a lone liner:

 perl -0777ne'print /^(?:.*\S.*\n(?:(?:(?!\n)\s)*\n){2})+.*\S.*\n/mg' file

---

If all your blank lines contain no whitespace, you can simplify some:

• Blank line: /^\n/m
• Non-blank line: /^.+\n/m

 perl -0777ne'print /^(?:.+\n\n\n)+.+\n/mg' file