Section: Tcl Built-In Commands (n)
history - Manipulate the history list
? ?arg arg ...
The history command performs one of several operations related to
recently-executed commands recorded in a history list. Each of
these recorded commands is referred to as an
When specifying an event to the history command, the following
forms may be used:
A number: if positive, it refers to the event with
that number (all events are numbered starting at 1). If the number
is negative, it selects an event relative to the current event
(-1 refers to the previous event, -2 to the one before that, and
so on). Event 0 refers to the current event.
A string: selects the most recent event that matches the string.
An event is considered to match the string either if the string is
the same as the first characters of the event, or if the string
matches the event in the sense of the string match command.
The history command can take any of the following forms:
as history info, described below.
- history add command ?exec?
Adds the command argument to the history list as a new event. If
exec is specified (or abbreviated) then the command is also
executed and its result is returned. If exec is not specified
then an empty string is returned as result.
- history change newValue ?event?
Replaces the value recorded for an event with newValue. Event
specifies the event to replace, and
defaults to the current event (not event -1). This command
is intended for use in commands that implement new forms of history
substitution and wish to replace the current event (which invokes the
substitution) with the command created through substitution. The return
value is an empty string.
- history clear
Erase the history list. The current keep limit is retained.
The history event numbers are reset.
- history event ?event?
Returns the value of the event given by event. Event
defaults to -1.
- history info ?count?
Returns a formatted string (intended for humans to read) giving
the event number and contents for each of the events in the history
list except the current event. If count is specified
then only the most recent count events are returned.
- history keep ?count?
This command may be used to change the size of the history list to
count events. Initially, 20 events are retained in the history
list. If count is not specified, the current keep limit is returned.
- history nextid
Returns the number of the next event to be recorded
in the history list. It is useful for things like printing the
event number in command-line prompts.
- history redo ?event?
Re-executes the command indicated by event and returns its result.
Event defaults to -1. This command results in history
revision: see below for details.
Pre-8.0 Tcl had a complex history revision mechanism.
The current mechanism is more limited, and the old
history operations substitute and words have been removed.
(As a consolation, the clear operation was added.)
The history option redo results in much simpler
When this option is invoked then the most recent event
is modified to eliminate the history command and replace it with
the result of the history command.
If you want to redo an event without modifying history, then use
the event operation to retrieve some event,
and the add operation to add it to history and execute it.
event, history, record