grep backslash in negative lookbehind

Question

I want to find the number of occurrences of XXX in my latex document that are not in the form of a command as \XXX. Therefore I am looking for occurrences that are not preceded by a backslash.

I tried the following:

grep -c -e '(?<!\)XXX' test.tex    #result: grep: Unmatched ) or \)
grep -c -e '(?<!\\)XXX' test.tex   #result: 0
grep -c -e "(?<!\\)XXX" test.tex   #result: -bash: !\\: event not found

none of them work as intended. In fact I don't understand the last error message at all.

My test.tex contains only the following lines

%test.tex

XXX

\XXX

So the expected result is 1.

Any ideas?

Ps.: I am working in bash.

Answer 1

Neither standard nor extended regular expressions support the look behind. Use Perl compatible regexes:

grep -P '(?<!\\)xxx' test.tex

Answer 2

Try to use

grep -P '(?<!\\)\bXXX\b' test.tex