BEGIN, eval {} and $^S

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

According to perlvar, $^S has three states: true, false or undefined. True inside eval, false elsewhere, or undefined if parsing is not finished. This has the effect of $^S always being undef when die occurs in a BEGIN block (or use.) I'm stuck at this point, so I need to find a way around it.

How do I know if my DIE handler is being called within an eval when parsing is not yet complete?

example:

BEGIN {
    $SIG{__DIE__} = sub {
        die @_ if $^S; # dont mess with eval.

        # ...my custom handler code...
        exit(0);
    }
    
    eval {
        die 'another day';
    };
    
    if ($@) {
        # execution never happens
    };
}

eval {
    die 'to day good';
};

if ($@) {
    # this works
};
[download]

Comment on BEGIN, eval {} and $^S Download Code

Replies are listed 'Best First'.
Re: BEGIN, eval {} and $^S by diotalevi (Canon) on Dec 17, 2003 at 00:39 UTC
Simple. See Re: Style Point: Catching eval { } errors.	[reply]
Re: Re: BEGIN, eval {} and $^S by eclark (Scribe) on Dec 17, 2003 at 02:57 UTC
Thats a good idea, I will use it in the future. It doesn't solve my problem because the DIE handler still wont know if it was called within `eval` or not.	[reply] [d/l]
Re: Re: Re: BEGIN, eval {} and $^S by diotalevi (Canon) on Dec 17, 2003 at 03:36 UTC
I think you'll have to pass that state to yourself via a global. How about something like $^S_FOR_REAL_AND_FOR_TRUE? You'd set it to something true prior to entering eval-string and clear it afterwards. You can inspect that during $SIG{__DIE__}.	[reply]
Re: BEGIN, eval {} and $^S by ysth (Canon) on Dec 17, 2003 at 08:02 UTC
You want something like: `sub in_eval { my $i=0; while (my @caller=caller($i++)) { return defined $caller[6] ? "eval EXPR" : "eval BLOCK" if !$caller[7] && $caller[3] eq "(eval)" } } ... die @_ if defined $^S ? $^S : in_eval;` [download] See perldoc caller for explanation. (I seem to recall there may be times when $^S is inaccurate; if so, just use `die @_ if in_eval`.)	[reply] [d/l] [select]


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