history(n) Tcl ( ) history(n)
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NAME
history - Manipulate the history list
SYNOPSIS
history ?option? ?arg arg ...?
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DESCRIPTION
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
``event''. When specifying an event to the history command,
the following forms may be used:
[1] 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).
[2] 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:
history
Same 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 isn't 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 event ?event?
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history(n) Tcl ( ) history(n)
Returns the value of the event given by event. Event
defaults to -1. This command causes history revision
to occur: see below for details.
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. This command returns an
empty string.
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 return
its result. Event defaults to -1. This command
results in history revision: see below for details.
history substitute old new ?event?
Retrieves the command given by event (-1 by default),
replace any occurrences of old by new in the command
(only simple character equality is supported; no wild
cards), execute the resulting command, and return the
result of that execution. This command results in
history revision: see below for details.
history words selector ?event?
Retrieves from the command given by event (-1 by
default) the words given by selector, and return those
words in a string separated by spaces. The selector
argument has three forms. If it is a single number
then it selects the word given by that number (0 for
the command name, 1 for its first argument, and so on).
If it consists of two numbers separated by a dash, then
it selects all the arguments between those two.
Otherwise selector is treated as a pattern; all words
matching that pattern (in the sense of string match)
are returned. In the numeric forms $ may be used to
select the last word of a command. For example,
suppose the most recent command in the history list is
format {%s is %d years old} Alice [expr $ageInMonths/12]
Below are some history commands and the results they
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history(n) Tcl ( ) history(n)
would produce:
history words $ [expr $ageInMonths/12]
history words 1-2{%s is %d years old} Alice
history words *a*o*{%s is %d years old} [expr $ageInMonths/12]
History words results in history revision: see below
for details.
HISTORY REVISION
The history options event, redo, substitute, and words
result in ``history revision''. When one of these options
is invoked then the current event is modified to eliminate
the history command and replace it with the result of the
history command. For example, suppose that the most recent
command in the history list is
set a [expr $b+2]
and suppose that the next command invoked is one of the ones
on the left side of the table below. The command actually
recorded in the history event will be the corresponding one
on the right side of the table.
history redo set a [expr $b+2]
history s a b set b [expr $b+2]
set c [history w 2]set c [expr $b+2]
History revision is needed because event specifiers like -1
are only valid at a particular time: once more events have
been added to the history list a different event specifier
would be needed. History revision occurs even when history
is invoked indirectly from the current event (e.g. a user
types a command that invokes a Tcl procedure that invokes
history): the top-level command whose execution eventually
resulted in a history command is replaced. If you wish to
invoke commands like history words without history revision,
you can use history event to save the current history event
and then use history change to restore it later.
KEYWORDS
event, history, record, revision
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