Add Apply Successive Filters To Lines In Less as a Unix TIL

unix/apply-successive-filters-to-lines-in-less.md

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+# Apply Successive Filters To Lines In Less
+
+Let's say I've opened a large Rails log file with `less`:
+
+```bash
+$ less logs/development.log
+```
+
+I have an idea of what I'm looking for, but there is way more noise than signal.
+I can start to filter out some of the noise. The `&` command starts a filter
+prompt. If I start to filter by something like `INSERT INTO`, then a ton of
+lines disappear leaving just those matching that pattern.
+
+Scrolling through the current set of lines, I start to have a better idea of
+what I'm looking for, but there is still too much noise. I can apply an
+additional successive filter on the remaining lines by hitting `&` again and
+entering in another pattern -- e.g. `GoodJob`.
+
+Now I only see lines that contain both `INSERT INTO` and `GoodJob` somewhere in
+them.
+
+As `less` puts it:
+
+> Multiple & commands may be entered, in which case only lines which match all
+> of the patterns will be displayed.
+
+If I want to undo all the filtering, I just need to enter an empty `&` filter
+prompt and it will reset things back to displaying all lines.
+
+> If pattern is empty (if you type & immediately followed by ENTER), any
+> filtering is turned off, and all lines are displayed.
+
+See `man less` for more details.