Use grep to report back only line numbers

Question

I have a file that possibly contains bad formatting (in this case, the occurrence of the pattern \\\\backslash). I would like to use grep to return

Answer 1

To count the number of lines matched the pattern:

grep -n "Pattern" in_file.ext | wc -l 

To extract matched pattern

sed -n '/pattern/p' file.est

To display line numbers on which pattern was matched

grep -n "pattern" file.ext | cut -f1 -d: