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A minibuffer history list records previous minibuffer inputs so the user can reuse them conveniently. It is a variable whose value is a list of strings (previous inputs), most recent first.
There are many separate minibuffer history lists, used for different kinds of inputs. It's the Lisp programmer's job to specify the right history list for each use of the minibuffer.
You specify a minibuffer history list with the optional history
argument to read-from-minibuffer or completing-read.
Here are the possible values for it:
Specifying 0 for startpos is equivalent to just specifying the
symbol variable. previous-history-element will display
the most recent element of the history list in the minibuffer. If you
specify a positive startpos, the minibuffer history functions
behave as if (elt variable (1- startpos)) were the
history element currently shown in the minibuffer.
For consistency, you should also specify that element of the history as the initial minibuffer contents, using the initial argument to the minibuffer input function (see Initial Input).
If you don't specify history, then the default history list
minibuffer-history is used. For other standard history lists,
see below. You can also create your own history list variable; just
initialize it to nil before the first use.
Both read-from-minibuffer and completing-read add new
elements to the history list automatically, and provide commands to
allow the user to reuse items on the list. The only thing your program
needs to do to use a history list is to initialize it and to pass its
name to the input functions when you wish. But it is safe to modify the
list by hand when the minibuffer input functions are not using it.
Emacs functions that add a new element to a history list can also
delete old elements if the list gets too long. The variable
history-length specifies the maximum length for most history
lists. To specify a different maximum length for a particular history
list, put the length in the history-length property of the
history list symbol. The variable history-delete-duplicates
specifies whether to delete duplicates in history.
This function adds a new element newelt, if it isn't the empty string, to the history list stored in the variable history-var, and returns the updated history list. It limits the list length to the value of maxelt (if non-
nil) orhistory-length(described below). The possible values of maxelt have the same meaning as the values ofhistory-length.Normally,
add-to-historyremoves duplicate members from the history list ifhistory-delete-duplicatesis non-nil. However, if keep-all is non-nil, that says not to remove duplicates, and to add newelt to the list even if it is empty.
If the value of this variable is
nil, standard functions that read from the minibuffer don't add new elements to the history list. This lets Lisp programs explicitly manage input history by usingadd-to-history. The default value ist.
The value of this variable specifies the maximum length for all history lists that don't specify their own maximum lengths. If the value is
t, that means there is no maximum (don't delete old elements). If a history list variable's symbol has a non-nilhistory-lengthproperty, it overrides this variable for that particular history list.
If the value of this variable is
t, that means when adding a new history element, all previous identical elements are deleted.
Here are some of the standard minibuffer history list variables:
A history list for arguments to
query-replace(and similar arguments to other commands).
A history list for arguments that are names of extended commands.