Execute function before exit of do() block

gri6507 has asked for the wisdom of the Perl Monks concerning the following question:

Fellow monks,

I have two script, main and helper, where the latter is executed by the former using a do() statement. I would like to do something on abnormal terminations of the helper. I tried using an END {} block withing the helper to do that, but unfortunately it seems to only execute on completion of the main script.

Here is my main script

use warnings;
use strict;

my $doItScript = $ARGV[0];

unless (my $return = do $doItScript)
{
    if ($@) { print "$doItScript: $@\n";}
    elsif (!defined($return)) { print "$doItScript: $!\n";}
    elsif (!$return) {print "could not execute $doItScript\n";}

}
print "Done with main\n";
[download]

Here is my helper script

use warnings;
use strict;
use Carp;

END {
    print "Good bye\n";
}

print "Hello\n";
croak "bad thing";
print "There\n";

1;
[download]

As expected, the helper "There" message is not printed, but the "Good bye" message is printed only after "Done with main". How can I reverse the order of those two events?

Comment on Execute function before exit of do() block Select or Download Code

Replies are listed 'Best First'.
Re: Execute function before exit of do() block by moritz (Cardinal) on Jan 29, 2014 at 19:04 UTC
One technique you can use is a "scope guard"; an object which goes out of scope when a scope is exited. When it goes out of scope, its reference count drops to zero and its DESTROY method is called: `# slave.pl: use 5.014; use warnings; my $CleanExit = 0; { package My::ScopeGuard; sub DESTROY { return if $CleanExit; say 'cleaning up slave.pl'; } } # this is the object that will go out of scope my $guard = bless {}, 'My::ScopeGuard'; say 'doing something'; die "Oh Noez"; # or if everything works fine: $CleanExit = 1;` [download] Now we can test it likes this: `$ perl -wE 'do "slave.pl"; say "Back in master"' doing something cleaning up slave.pl Back in master` [download] You can see that the cleanup happens before the the rest of the calling code. Perl 6 - the future is here, just unevenly distributed	[reply] [d/l] [select]
Re^2: Execute function before exit of do() block by shmem (Chancellor) on Jan 29, 2014 at 20:58 UTC
I've been thinking about this, too, prior to writing my `$SIG{__DIE__}` answer above. sigh Creating a sentinel object... slowly, the objectification creeps on every subject... perl -le'print map{pack c,($-++?1:13)+ord}split//,ESEL'	[reply] [d/l]
Re^3: Execute function before exit of do() block by moritz (Cardinal) on Jan 29, 2014 at 21:04 UTC
Well, in Perl 6 there are are non-object options, like a LEAVE block that is called on every scope exit, or an `UNDO` block for unsuccessful scope exists. I wonder if those are possible (and worthy) to backport to perl 5... Perl 6 - the future is here, just unevenly distributed	[reply] [d/l]
Re^4: Execute function before exit of do() block by ikegami (Patriarch) on Jan 30, 2014 at 00:28 UTC
Re^4: Execute function before exit of do() block by shmem (Chancellor) on Jan 29, 2014 at 21:11 UTC
Re^3: Execute function before exit of do() block by ikegami (Patriarch) on Jan 30, 2014 at 00:22 UTC
You could use clear or free magic if you wanted to avoid objects.	[reply]
Re: Execute function before exit of do() block by choroba (Cardinal) on Jan 29, 2014 at 17:51 UTC
If you study the documentation of do, you can notice it behaves as eval. It means, you can check the problems in the calling script. If you want to check the problems in the called script, you can use `eval`: `eval { print "Hello\n"; croak "bad thing"; print "There\n"; 1 } and print "Good bye\n";` [download] See also Try::Tiny. لսႽ† ᥲᥒ⚪⟊Ⴙᘓᖇ Ꮅᘓᖇ⎱ Ⴙᥲ𝇋ƙᘓᖇ	[reply] [d/l] [select]
Re^2: Execute function before exit of do() block by gri6507 (Deacon) on Jan 29, 2014 at 17:57 UTC
My main script is generic and can "execute" many different types of helper scripts. Not all helper scripts need (or even can) act on the detected bad event. That is why the detection of the bad event needs to happen inside the helper script, rather than the main script. Your solution would not work in my case.	[reply]
Re^3: Execute function before exit of do() block by shmem (Chancellor) on Jan 29, 2014 at 18:04 UTC
Not all helper scripts need (or even can) act on the detected bad event. That is why the detection of the bad event needs to happen inside the helper script, rather than the main script. What would detection of the bad event (...) inside the helper script script give you, if that helper script cannot act on the detected bad event as you are saying? Error detection has to happen in the main script, checking the for `$@` as you already do. perl -le'print map{pack c,($-++?1:13)+ord}split//,ESEL'	[reply] [d/l]
Re^4: Execute function before exit of do() block by gri6507 (Deacon) on Jan 29, 2014 at 18:11 UTC
Re^5: Execute function before exit of do() block by shmem (Chancellor) on Jan 29, 2014 at 20:35 UTC
Re^3: Execute function before exit of do() block by choroba (Cardinal) on Jan 29, 2014 at 21:54 UTC
Your solution would not work in my case. I proposed two solutions. Which one do you mean? لսႽ† ᥲᥒ⚪⟊Ⴙᘓᖇ Ꮅᘓᖇ⎱ Ⴙᥲ𝇋ƙᘓᖇ	[reply]
Re: Execute function before exit of do() block by Laurent_R (Canon) on Jan 29, 2014 at 18:25 UTC
I do not know what your helper script is doing, but if the two scripts are independent, maybe you could use the `system` command to launch your second script and check the exit status of the child.	[reply] [d/l]


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