I have a file (a log) with unique identifiers. I know I can exclude a single unique identifier in emacs using M-x flush-lines. I sometimes need to exclude more than one unique identifier, and for up to ten or twenty this is not a problem as I can do it by hand. This is usually sufficient for my needs. However, there is the occasional need to exclude significantly more. Today, for instance, I need to exclude some 80k instances of unique identifiers (out of a file that might have over 300k unique ids. (I'm trying to locate the proverbial needle in a haystack and have a way to identify one kind of 'not needle' that is present 'and now I need a way to get them out of the way quickly)

Is there a way to loop through flush-lines over a list of regex? (and when I say 'loop', I'm purely being descriptive: I don't, necessarily, mean the function loop. I'm given to understand 'while' and 'dolist' are similar functions... I don't know how to use any of them in this case)


  • 1
    Just to clarify, do you mean you want to run flush-lines 80K times, each time with a different regexp? This might be easier to do from the command line via grep -v.
    – Tyler
    Feb 27, 2017 at 21:53
  • Yes, Tyler, that's essentially what I mean. I thought of the grep -v (egrep, actually) option but each instance of exclusion leaves me with a file that thats got the remaining 79,999 regex 's and I have to, it seems to me, iterate on the file creation. Much simpler, I would think, to let emacs buffer manage to do it... But, as you may have gueessed, I'm not a programmer...
    – Petr
    Feb 27, 2017 at 22:00
  • This might get you started: gist.github.com/plantarum/80937e21cde1f51764ee3727f92a50a6
    – Tyler
    Feb 27, 2017 at 22:16
  • 1
    Certainly you can do what you want. Obtain a list of the identifiers (from reading a file or whatever), then use dolist over the list, calling flush-lines for each (from point-min each time). This is just as easy and performant as combining them into a single regexp \(foo\|bar\|...\) and using a single invocation of flush-lines. (And such a large combination regexp might lead to regexp overflow.)
    – Drew
    Feb 27, 2017 at 23:50

1 Answer 1


You might like to read those 80K identifiers, then combine them into a single regexp with regexp-opt and then pass that to a single flush-lines call. This said, maybe it'll fail because the resulting regexp is too large (Emacs has a limit on the size of its regexps).

  • 1
    Note that regexp-opt takes literal strings, not regexps. If you include e.g. an anchor in your regexps you'll have to factor it out.
    – YoungFrog
    Feb 28, 2017 at 8:32

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