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

You're going to want the second field after the colon, not the first.

grep -n "text to find" file.txt | cut -f2 -d:

Answer 2

Bash version

    lineno=$(grep -n "pattern" filename)
    lineno=${lineno%%:*}