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Reading An Entire Text File

Problem

You want to read the lines from a file and store them in a list.

Solution

readlines(FileName) ->
    {ok, Device} = file:open(FileName, [read]),
    get_all_lines(Device, []).

get_all_lines(Device, Accum) ->
    case io:get_line(Device, "") of
        eof  -> file:close(Device), Accum;
        Line -> get_all_lines(Device, Accum ++ [Line])
    end.

Discussion

This recipe is suspiciously similar to FileReadingLines. For a more general solution, have a look at FileCountLines.

This recipe can be rather slow for larger files. The problem is that the append operation must traverse the list in order to append the new line. As the list grows, this takes longer and longer. It is probably better to build the list in reverse order and then reverse it at the end:

get_all_lines(Device, Accum) ->
    case io:get_line(Device, "") of
        eof  -> file:close(Device), lists:reverse(Accum);
        Line -> get_all_lines(Device, [Line|Accum])
    end.

Comments about this recipe

Contributors

Based on work by GordonWeakliem.

-- BrentAFulgham - 03 Sep 2004

-- MarkWutka - 07 Feb 2006 (Added reverse list accumulation)