For 2023 - we are now fully retired from IT training. We have made many, many friends over 25 years of teaching about Python, Tcl, Perl, PHP, Lua, Java, C and C++ - and MySQL, Linux and Solaris/SunOS too. Our training notes are now very much out of date, but due to upward compatability most of our examples remain operational and even relevant ad you are welcome to make us if them "as seen" and at your own risk.
Lisa and I (Graham) now live in what was our training centre in Melksham - happy to meet with former delegates here - but do check ahead before coming round. We are far from inactive - rather, enjoying the times that we are retired but still healthy enough in mind and body to be active!
I am also active in many other area and still look after a lot of web sites - you can find an index ((here)) |
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)
Some other Articles
Melksham Oak Community School, Melksham, WiltshireTeam changes at Well House - looking forwardFlash (client) to PHP (server) - exampleIntroduction to Object Oriented ProgrammingPreventing ^C stopping / killing a program - PerlMaking it all worthwhileFlurinci knows Raby Lae PHP and JeveRomeo and JulieTransition
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This is a page archived from The Horse's Mouth at
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the diary and writings of Graham Ellis.
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