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For 2021 - online Python 3 training - see ((here)).

Our plans were to retire in summer 2020 and see the world, but Coronavirus has lead us into a lot of lockdown programming in Python 3 and PHP 7.
We can now offer tailored online training - small groups, real tutors - works really well for groups of 4 to 14 delegates. Anywhere in the world; course language English.

Please ask about private 'maintenance' training for Python 2, Tcl, Perl, PHP, Lua, etc.
Preventing ^C stopping / killing a program - Perl

Here's a demonstration - in Perl - that shows you how to avoid a ^C (Control C) dropping you straight out of a program.

Have you ever accidentally hit ^C in the wrong window and terminated a long-running process just before it finished ... well, by setting $SIG{INT} to the address of a sub you want to run, you can divert the signal in Perl. The example code here simulates a long running process with a loop of 60 short sleeps (naps?) ...

$SIG{"INT"} = \&nowayjose;
 
$| = 1;
 
for (1..60){
  print "dot";
  sleep 1;
 
  if ($rq) {
    exit if (time() - $recent < 4) ;
    print "\nNah\n";
    $rq = 0;
    $recent = time();
    }
  }
 
sub nowayjose {
  $rq = 1;
  }


You'll note that all my extra "sub" does is set a flag so that the interrupt can be nicely handled at the end of the loop, that the handler turns the interrupt flag back off, and that I've written the program so that a second ^C within 4 seconds WILL cause it to exit.

As an afterthought ... if you disable ^C completely (i.e. if you don't use the 4 second trick), how will you get out of the program? Well ... you'll still be able to suspend it with ^Z then kill it with kill %1, or you'll be able to find its process id and use a kill -9
(written 2008-12-05, updated 2008-12-07)

 
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
P667 - Perl - Handling Huge Data
  [639] Progress bars and other dynamic reports - (2006-03-09)
  [762] Huge data files - what happened earlier? - (2006-06-15)
  [975] Answering ALL the delegate's Perl questions - (2006-12-09)
  [1397] Perl - progress bar, supressing ^C and coping with huge data flows - (2007-10-20)
  [1920] Progress Bar Techniques - Perl - (2008-12-03)
  [2376] Long job - progress bar techniques (Perl) - (2009-08-26)
  [2805] How are you getting on? - (2010-06-13)
  [2806] Macho matching - do not do it! - (2010-06-13)
  [2834] Teaching examples in Perl - third and final part - (2010-06-27)
  [3374] Speeding up your Perl code - (2011-07-30)
  [3375] How to interact with a Perl program while it is processing data - (2011-07-31)


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This is a page archived from The Horse's Mouth at http://www.wellho.net/horse/ - the diary and writings of Graham Ellis. Every attempt was made to provide current information at the time the page was written, but things do move forward in our business - new software releases, price changes, new techniques. Please check back via our main site for current courses, prices, versions, etc - any mention of a price in "The Horse's Mouth" cannot be taken as an offer to supply at that price.

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