history.n

linux系统下的音频通信

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'\" Copyright (c) 1993 The Regents of the University of California.
'\" Copyright (c) 1994-1997 Sun Microsystems, Inc.
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'\" SCCS: @(#) history.n 1.11 97/08/07 16:44:49
'\" 
.so man.macros
.TH history n "" Tcl "Tcl Built-In Commands"
.BS
'\" Note:  do not modify the .SH NAME line immediately below!
.SH NAME
history \- Manipulate the history list
.SH SYNOPSIS
\fBhistory \fR?\fIoption\fR? ?\fIarg arg ...\fR?
.BE

.SH DESCRIPTION
.PP
The \fBhistory\fR 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 \fBhistory\fR command, the following
forms may be used:
.IP [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
(\fB\-1\fR refers to the previous event, \fB\-2\fR to the one before that, and
so on).  Event \fB0\fP refers to the current event.
.IP [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 \fBstring match\fR command.
.PP
The \fBhistory\fR command can take any of the following forms:
.TP
\fBhistory\fR
Same
as \fBhistory info\fR, described below.
.TP
\fBhistory add\fI command \fR?\fBexec\fR?
Adds the \fIcommand\fR argument to the history list as a new event.  If
\fBexec\fR is specified (or abbreviated) then the command is also
executed and its result is returned.  If \fBexec\fR isn't specified
then an empty string is returned as result.
.TP
\fBhistory change\fI newValue\fR ?\fIevent\fR?
Replaces the value recorded for an event with \fInewValue\fR.  \fIEvent\fR
specifies the event to replace, and
defaults to the \fIcurrent\fR event (not event \fB\-1\fR).  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.
.TP
\fBhistory clear\fR
Erase the history list.  The current keep limit is retained.
The history event numbers are reset.
.TP
\fBhistory event\fR ?\fIevent\fR?
Returns the value of the event given by \fIevent\fR.  \fIEvent\fR
defaults to \fB\-1\fR.
.TP
\fBhistory info \fR?\fIcount\fR?
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 \fIcount\fR is specified
then only the most recent \fIcount\fR events are returned.
.TP
\fBhistory keep \fR?\fIcount\fR?
This command may be used to change the size of the history list to
\fIcount\fR events.  Initially, 20 events are retained in the history
list.  If \fIcount\fR is not specified, the current keep limit is returned.
.TP
\fBhistory nextid\fR
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.
.TP
\fBhistory redo \fR?\fIevent\fR?
Re-executes the command indicated by \fIevent\fR and return its result.
\fIEvent\fR defaults to \fB\-1\fR.  This command results in history
revision:  see below for details.
.SH "HISTORY REVISION"
.PP
Pre-8.0 Tcl had a complex history revision mechanism.
The current mechanism is more limited, and the old
history operations \fBsubstitute\fP and \fBwords\fP have been removed.
(As a consolation, the \fBclear\fP operation was added.)
.PP
The history option \fBredo\fR results in much simpler ``history revision''.
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 \fBevent\fP operation to retrieve some event,
and the \fBadd\fP operation to add it to history and execute it.

.SH KEYWORDS
event, history, record