history(3Tcl) history(3Tcl)
history - Manipulate the history list
history ?option? ?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 ``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?
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.
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history(3Tcl) history(3Tcl)
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 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
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history(3Tcl) history(3Tcl)
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.
event, history, record, revision
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