regex - How to find patterns across multiple lines using grep?

Question

I want to find files that have "abc" AND "efg" in that order, and those two strings are on different lines in that file. Eg: a file with content:

blah blah..
blah blah..
blah abc blah
blah blah..
blah blah..
blah blah..
blah efg blah blah
blah blah..
blah blah..

Should be matched.

Answer 1

Grep is not sufficient for this operation.

pcregrep which is found in most of the modern Linux systems can be used as

pcregrep -M  'abc.*(
|.)*efg' test.txt

where -M, --multiline allow patterns to match more than one line

There is a newer pcre2grep also. Both are provided by the PCRE project.

pcre2grep is available for Mac OS X via Mac Ports as part of port pcre2:

% sudo port install pcre2 

and via Homebrew as:

% brew install pcre

or for pcre2

% brew install pcre2

pcre2grep is also available on Linux (Ubuntu 18.04+)

$ sudo apt install pcre2-utils # PCRE2
$ sudo apt install pcregrep    # Older PCRE