jmccaf01 has asked for the wisdom of the Perl Monks concerning the following question:

My query has to do with how one would stop perl from accepting 3 carraige returns when one enters Ctrl-C and decides to resume the programme..

# ./prompt2
Testing One Two Three
^CPress -=ENTER=- to Resume or 'q' to quit
<ENTER * 3 times>
Got to the end of the programme

Here is the code
#!/usr/bin/perl
$SIG{'INT'} = sub {
print "Press -=ENTER=- to Resume or 'q' to quit\n";
chomp (my $quit=<STDIN>);
die "\nTerminating at users request \n" if $quit =~ /^q$/i;
};
print "Testing One Two Three\n";
chomp (my $continue=<STDIN>);
print "Got to the end of the programme \n";

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janitored by ybiC: Balanced <code> tags around codeblock, other minor format tweaks for legibility

Replies are listed 'Best First'.
Re: Resuming from a SIG{INT}
by tinita (Parson) on Mar 16, 2004 at 17:26 UTC
    i would suggest that another CTRL-C would terminate the program as i think that's more common practice, but anyway -
    if you want to decide if the user entered 3 empty lines (or CRs) or a single character 'q' you'd have to use Term::ReadKey and maybe Term::ReadLine.
[reply]
Re: Resuming from a SIG{INT}
by NetWallah (Canon) on Mar 16, 2004 at 17:13 UTC
    Your code does not take "3 carriage returns".

    A single CR after CTRL-C DOES quit the program with the correct message (as coded) "Got to the end of the programme".

    Offense, like beauty, is in the eye of the beholder, and a fantasy.
    By guaranteeing freedom of expression, the First Amendment also guarntees offense.

[reply]
Re: Resuming from a SIG{INT}
by Limbic~Region (Chancellor) on Mar 16, 2004 at 19:26 UTC
    jmccaf01,
    I assure you that your code is working as you have coded it. I just think you didn't code it the way you wanted it. Try the following instead: 
    #!/usr/bin/perl
use strict;
use warnings;

$SIG{INT} = sub {
    print "Program interuption detected!\n";
    print "Press ENTER to continue or any other key to quit\n";
    my $foo = <STDIN>;
    chomp $foo;
    die "\nTerminating at users request\n" if $foo;
    print "Resuming our regularly scheduled programming\n";
};

print "This would be your program starting up\n";
for ( 1 .. 10 ) {
    print "$_\n" for 1 .. 10;
    sleep 1;
}
print "This would be your program finishing cleanly\n";

    [download]
    Cheers - L~R
[reply]
[d/l]
      You cheat :)

      Your example shows that if a signal handler that uses diamond operator is lucky enough not to interrupt another diamond operator it will probably usually most of the time work as expected.

[reply]
        kappa,
        We completely have different interpretations of why the OP chose to read from STDIN during the main execution of the program. I was assuming it was to get the program to pause long enough to test and it was the extra carriage return(s) that were not desired.

        Cheers - L~R

[reply]
Re: Resuming from a SIG{INT}
by kappa (Chaplain) on Mar 16, 2004 at 20:34 UTC
    Please read perldoc -q signal. You should not do anything serious from a signal handler, especially use buffered IO.
[reply]
[d/l]
Re: Resuming from a SIG{INT}
by chip (Curate) on Mar 16, 2004 at 16:30 UTC
    Please explain more about the behavior you see vs. the behavior you want.

        -- Chip Salzenberg, Free-Floating Agent of Chaos

[reply]
      If one enters Ctrl-C and decides to resume the programme a single Carraige Return should be ok.
      At present it does not behave the way I expected it to.

[reply]
        The first Enter is actually making the program continue. But after returning, Perl seems to require two Enters for the <STDIN> in the main program to return.

        I have no idea why this is so. I suspect it's a bug.

            -- Chip Salzenberg, Free-Floating Agent of Chaos

[reply]

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