grep to find instances of "Foo" where "Bar" does not appear within 10 lines

Question

Suppose I want to search an entire tree for all CPP files where "Foo" occurs. I might do:

find . -name "*.cpp" | xargs grep "Foo"

Now suppose I want to list only those instances where some other string, say "Bar" does not occur within 3 lines of the previous result.

So given two files:

a.cpp

1 Foo
2 qwerty
3 qwerty

b.cpp

1 Foo
2 Bar
3 qwerty

I would like to construct a simple search where "Foo" from a.cpp is found, but "Foo" from b.cpp is not.

Is there a way to accomplish this in a fairly simple way?

Answer 1

With pcregrep:

pcregrep --include='\.cpp$' -rnM 'Foo(?!(?:.*\n){0,2}.*Bar)' .

The key is in the -M option which is unique to pcregrep and is used to match multiple lines (pcregrep pulls more data from the input file as necessary when walking the RE demands it).

(?!...) is the perl/PCRE negative look-ahead RE operator. Foo(?!...) matches Foo as long as ... does not match what follows.

... being (?:.*\n){0,2}.*Bar (. not matching a newline character), that is from 0 to 2 lines followed by a line containing Bar.

Answer 2

Never mind, just use pcregrep as suggested by @StephaneChazelas.

---

This should work:

$ find . -name "*.cpp" | 
    while IFS= read -r file; do 
      grep -A 3 Foo "$file" | grep -q Bar || echo "$file"; 
    done 

The idea is to use grep's -A switch to output the matched lines and the N following lines. You then pass the result through a grep Bar and if that does not match (exit > 0), then you echo the name of the file.

If you know you have sane file names (no spaces, new lines or other weird characters), you can simplify to:

$ for file in $(find . -name "*.cpp"); do 
   grep -A 3 Foo "$file" | grep -q Bar || echo "$file"; 
  done 

---

For example:

terdon@oregano foo $ cat a.cpp 
1 Foo
2 qwerty
3 qwerty
terdon@oregano foo $ cat b.cpp 
1 Foo
2 Bar
3 qwerty
terdon@oregano foo $ cat c.cpp 
1 Foo
2 qwerty
3 qwerty
4 qwerty
5. Bar
terdon@oregano foo $ for file in $(find . -name "*.cpp"); do grep -A 3 Foo "$file" | grep -q Bar || echo "$file"; done 
./c.cpp
./a.cpp

Note that c.cpp is returned despite containing Bar because the line with Bar is more than 3 lines after Foo. You cna control the number of lines you want to search by changing the value passed to -A:

$ for file in $(find . -name "*.cpp"); do 
   grep -A 10 Foo "$file" | grep -q Bar || echo "$file"; 
  done 
./a.cpp

---

Here's a shorter one (assuming you use bash):

$ shopt -s globstar 
$ for file in **/*cpp; do 
    grep -A 10 Foo "$file" | grep -q Bar || echo "$file"; 
  done

---

IMPORTANT

As Stephane Chazelas pointed out in the comments, the above solutions will also print files that don't contain Foo at all. This one avoids that:

for file in **/*cpp; do 
  grep -qm 1 Foo "$file" && 
  (grep -A 3 Foo "$file" | grep -q Bar || echo "$file"); 
done

Answer 3

Untested, I'm on my phone :

find . -name "*.cpp" | xargs awk '/foo/{t=$0;c=10}/bar/{c=0;t=""}c{c--}t&&!c{print t;t=""}END&&t{print t}' 

something like that.