CODEWITHSUNDEEP
perldebugging
Vic K
Vic K

Reputation: 135

How does a Perl script know if it's running in the debugger?

I have a script that redirects STDIN/STDOUT to a file normally. But, debugging is a lot more efficient if it doesn't do that. Is there a $DB:xxx variable or something that lets the script know so it can behave differently?

Upvotes: 5

Views: 384

Answers (4)

kovacsbv
kovacsbv

Reputation: 351

Both of these are useful for what I was doing. I'll put it on my Perl cheat sheet.

if ( $INC{ "perl5db.pl" } ) {
   say "Debugger is running";
}

if ( $^P ) {
   say "Perl is in debug support mode";
}

Upvotes: 0

Eugen Konkov
Eugen Konkov

Reputation: 25133

To find that your script is under debugger you need to check: $^P variable:

if ( $^P ) {
    # running under a debugger
}

https://perldoc.perl.org/perldebug#Calling-the-Debugger

If you script was run without -d option then $DB::single does noting.

According to the documentation the minimal debugger is sub DB::DB {}.
So another method to check that your script is under debugger is:

if( defined &DB::DB ){
   # running under a debugger
}

Upvotes: 1

gugod
gugod

Reputation: 830

Reading through the perl source code of DB.pm (perldoc -m DB), I noticed that $SIG{INT} is globally set at the end.

This seems to work, at least for a trivial program:

if (\&DB::catch && $SIG{'INT'} && $SIG{'INT'} == \&DB::catch) {
    say "Debugging ?"
}

If it's not applicable, I guess it's possible to subclass DB.pm and create a simple debugger which overrides cont and does extra bookkeeping.

Upvotes: 1

ikegami
ikegami

Reputation: 385657

I didn't find any way of determining if they debugger is running directly, but you could check if well-known debugger variable $DB::single exists using the following:

if ( $DB::{ single } ) {
   say "Debugger is running";
}

Another approach would be to check if the debugger module is loaded.

if ( $INC{ "perl5db.pl" } ) {
   say "Debugger is running";
}

Finally, the debugger requires that Perl is running in debug support mode, and $^P indicates whether Perl is in this mode or not.

if ( $^P ) {
   say "Perl is in debug support mode";
}

The debugger isn't the only tool that requires putting Perl in debug support mode. Others include Devel::NYTProf, Devel::Cover, Devel::Trace, and more. So this approach can't be used to specifically check if the debugger is running. But it might be what you actually want.

Upvotes: 4

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