[bug #68645] Confusing rules on appending to HISTFILE

URL:
  <https://savannah.gnu.org/bugs/?68645>

                 Summary: Confusing rules on appending to HISTFILE
                   Group: The GNU Bourne-Again SHell
               Submitter: ilya_the_human
               Submitted: Tue 25 Aug 2026 04:19:48 PM UTC
                Category: None
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: None
                  Status: None
                 Privacy: Public
             Assigned to: None
             Open/Closed: Open
         Discussion Lock: Unlocked


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Follow-up Comments:


-------------------------------------------------------
Date: Tue 25 Aug 2026 04:19:48 PM UTC By: Ilya <ilya_the_human>
Reference says
```
When a shell with history enabled exits, Bash copies the last $HISTSIZE
entries from the history list to the file named by $HISTFILE. If the
histappend shell option is set (see Bash Builtin Commands), Bash appends the
entries to the history file, otherwise it overwrites the history file.
```

But if we look at the code (bashhist.c:512-523), we see that the history does
not work like that at all, and append happens basically always 
```
	  using_history ();
	  if (history_lines_this_session <= where_history () ||
force_append_history)
	    {
	      result = append_history (history_lines_this_session, hf);
	      history_lines_in_file += history_lines_this_session;
	    }
	  else
	    {
	      result = write_history (hf);
	      history_lines_in_file = history_lines_written_to_file;
	      /* history_lines_in_file = where_history () + history_base - 1; */
	    }
```
the only case when the history is actually overwritten is as follows - in one
session I write more commands (history_lines_this_session) than HISTSIZE
(where_history(), which returns history_length), which is a pretty improbable
scenario. I don't at all understand why it is this way

I suppose the historic behavior better be preserved, so I will not offer a
potential fix (which I feel would be to remove `history_lines_this_session <=
where_history ()` condition?), but the docs at least should be patched.
Current text is extremely confusing, in reality "histappend" opt feels mostly
redundant 

P.S. the phrase "copies the last $HISTSIZE entries from the history list"
itself also sounds weird, since the history list is already no more than
$HISTSIZE elements long







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