Also while inside less: & shows you only lines which match a pattern. You can hit & multiple times and less will show you only those lines which match every input pattern. A ^N right after & negates the pattern. & respects the -I switch (case insensitive pattern matching).
I use this all the time, especially when I'm on a machine that I don't want to bother installing something like fzf on.
Seems to depend on your particular less, see the last sentence of this paragraph from `man less` on my machine:
&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. Multiple & commands may be entered, in which case only
lines which match all of the patterns will be displayed.
Indeed, I thought it would behave like you describe.. when I was refreshing my memory of how the negative pattern filtering worked, I first did &/pattern and then &/^Npattern, and was surprised to see that it displayed zero matching lines.
this is my version of less:
% less --version
less 581.2 (POSIX regular expressions)
Copyright (C) 1984-2021 Mark Nudelman
