How do I use ack's --ignore-file option?

Question

If I put

--ignore-file=example.txt

into my .ackrc or on the ack command-line, I get the error message "Invalid filter specification "example.txt".

The ack documentation says that the --ignore-file option takes a filter as an argument. What's a filter? How do I use --ignore-file to simply ignore a file?

Answer 1

Use is:filename as your filter:

--ignore-file=is:example.txt

Filters are the same as ack type definitions and can be a literal filename with is, a file extention with ext, or a regular expression to match.