display changing variable in one place on screen in ksh

09-25-2008

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ksh93 has the undocumented alarm feature which can be used to display something or do something on a regular basis.

Here is a trivial example to display the time on every second

Code:

#!/usr/bin/ksh93

alarm -r a +1
function a.alarm { print -n "$(date +%H:%S)\r"; }
read dummy      # wait

From an email by Dave Korn ...

Quote:

alarm remains undocumented since I have not decided what interface I want for this functionality. ksh93 has the ability to handle multiple timeout events and alarm is a built-in that can enable them.
.....
Usage: alarm [-r] [varname seconds] where -r means periodically, varname is a variable name, and seconds can be of absolute from the epoch or of the form +n.

In addition, the alarm builtin allows the alarm discipline function to be specified which gets invoked when the timer goes off. For example, if you have the title function (which is distributed with ksh93, and which updates the title bar, then

alarm -r var +1
function var.alarm
{
title $(printf "%T")
}

will update the title bar with the current date/time every second.

fpmurphy

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times(1) User Commands times(1) NAME
times - shell built-in function to report time usages of the current shell SYNOPSIS
sh times ksh times DESCRIPTION
sh Print the accumulated user and system times for processes run from the shell. ksh Print the accumulated user and system times for the shell and for processes run from the shell. On this man page, ksh(1) commands that are preceded by one or two * (asterisks) are treated specially in the following ways: 1. Variable assignment lists preceding the command remain in effect when the command completes. 2. I/O redirections are processed after variable assignments. 3. Errors cause a script that contains them to abort. 4. Words, following a command preceded by ** that are in the format of a variable assignment, are expanded with the same rules as a vari- able assignment. This means that tilde substitution is performed after the = sign and word splitting and file name generation are not performed. ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Availability |SUNWcsu | +-----------------------------+-----------------------------+ SEE ALSO
ksh(1), sh(1), time(1), attributes(5) SunOS 5.10 15 Apr 1994 times(1)

Shell Programming and Scripting

display changing variable in one place on screen in ksh

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