less-like pager with filter feature?

Question

I'd like to have a pager program, similar to less, with the following added commands:

• Prompt for a regular expression and display only lines that match it;
• Prompt for a regular expression and remove from the current display lines that match it; and
• Revert to showing the entire file.
• Show the current filters.

Another nice feature would be an optional visual indication that lines have been hidden.

Filtering the input to `less, as in:

grep pattern filename | less

is only a partial solution. It's missing the ability to easily reconfigure the filtering without exiting and restarting the pager.

I'm looking for something that works in text mode, though a GUI tool would also be helpful.

I've taken a quick look at the most pager, and it doesn't seem to have such a feature.

Ideally I'd like to see this as a new feature in a future release in less. I might contact the maintainer with a suggestion. Meanwhile, does such a thing already exist?

Answer 1

Well, this is a little embarrassing.

I suggested this feature to Mark Nudelman, the maintainer of the less command. His response:

Is there something in this request that isn't already handled by the & command?

I've somehow managed to use less for several decades without noticing that that command exists.

Here's the documentation:

&pattern

Display only lines which match the pattern; lines which do not match the pattern are not displayed. If pattern is empty (if you type & immediately followed by ENTER), any filtering is turned off, and all lines are displayed. While filtering is in effect, an ampersand is displayed at the beginning of the prompt, as a reminder that some lines in the file may be hidden.

Certain characters are special as in the / command:

^N or !
Display only lines which do NOT match the pattern.

^R
Don't interpret regular expression metacharacters; that is, do a simple textual comparison.