Re: Using the perl debugger

[ww]

Clumsy, but use {{ at the debugger prompt before the line(s) you want to "skip over."

Line 25 below, set the "pre-debugger" command to an octothorpe, effectively turning the line in the next debugger step into a comment. You can see the effect at 29.

Line 35 is one way of showing yourself what "pre-debugger" commands are in effect; Line 43 clears all "pre-debugger" commands.

#!/usr/bin/perl
use strict;
use warnings;

my @i = (2..5);

for my $i (@i) {
  $i ++;
  print "foo";
  print " $i\n";
}


=head running under debug:

>perl -d pl_test\test{{.pl

Loading DB routines from perl5db.pl version 1.28
Editor support available.

Enter h or `h h' for help, or `perldoc perldebug' for more help.

main::(pl_test\test{{.pl:5):
5:      my @i = (2..5);
  DB<1> {{ #
  DB<2> s
main::(pl_test\test{{.pl:7):
7:      for my $i (@i) {
auto(-1)  DB<2> #

  DB<2> s
 
  ...

  DB<2> {{
pre-debugger commands:
        {{ -- #
  DB<3> s
foomain::(pl_test\test{{.pl:10):
10:       print " $i\n";
auto(-1)  DB<3> #

  DB<3> { *
All { actions cleared.
  DB<4>

  ... continue normally

=cut

Update: bolded the first {{ in the narrative.

[almut]

use {{ ... effectively turning the line in the next debugger step into a comment.

I don't think this has the desired effect of commenting out the lines. Rather, it runs the debugger command "#" (which does nothing of interest) before running the line itself. Even if you'd use pre-Perl actions (i.e. <), they would still be executed separately, rather than being textually merged with the line(s) in question (as would be required to comment out).

Try skipping over the $i++, for example... the subsequent print " $i\n" will still print the incremented value (e.g. 3, not 2, on the first iteration).

An example application of pre-debugger commands would be setting "{ l" to get a listing of the next few lines on every prompt.

[codeacrobat]

Unfortunately it doesn't work in perl5db.pl v1.30 :-( After "{{ #" statements are still getting executed.

$ perl -v

This is perl, v5.10.0 built for cygwin-thread-multi-64int
(with 6 registered patches, see perl -V for more detail)

$ perl -d bla.pl

Loading DB routines from perl5db.pl version 1.3
Editor support available.

Enter h or `h h' for help, or `man perldebug' for more help.

main::(bla.pl:5):       my @i = (2..5);
  DB<1> {{ #
  DB<2> s
main::(bla.pl:7):       for my $i (@i) {
auto(-1)  DB<2> #

  DB<2> s
main::(bla.pl:8):          $i ++;
auto(-1)  DB<2> #

  DB<2> s
main::(bla.pl:9):          print "foo";
auto(-1)  DB<2> #

  DB<2> s
main::(bla.pl:10):         print " $i\n";
auto(-1)  DB<2> #
foo

[ww]

Ooops! The behavior appears to vary depending on how lines are executed, leading me to believe almut may be correct and that codeacrobat's observation may apply to 5.8.8 (and probably others). A caveat (or "confusion") follows. Compare using r instead of stepping:

>perl -d \pl_test\test{{.pl

Loading DB routines from perl5db.pl version 1.28
Editor support available.

Enter h or `h h' for help, or `perldoc perldebug' for more help.

main::(\pl_test\test{{.pl:5):
5:      my @i = (2..5);
  DB<1> {{ #
  DB<2> r
foo 3
foo 4
foo 5
foo 6
Debugged program terminated.  Use q to quit or R to restart,
  use o inhibit_exit to avoid stopping after program termination,
  h q, h R or h o to get additional info.
auto(-1)  DB<2> #

  DB<2>
...

BUT, stepping (entirely) through the script:

BUT:

>perl -d pl_test\test{{.pl

Loading DB routines from perl5db.pl version 1.28
Editor support available.

Enter h or `h h' for help, or `perldoc perldebug' for more help.

main::(pl_test\test{{.pl:5):
5:      my @i = (2..5);
  DB<1> {{ #
  DB<2> s
main::(pl_test\test{{.pl:7):
7:      for my $i (@i) {
auto(-1)  DB<2> #

  DB<2>
main::(pl_test\test{{.pl:8):
8:        $i ++;
auto(-1)  DB<2> #

  DB<2>
main::(pl_test\test{{.pl:9):
9:        print "foo";
auto(-1)  DB<2> #

  DB<2>
foomain::(pl_test\test{{.pl:10):
10:       print " $i\n";
auto(-1)  DB<2> #

  DB<2>
 3
main::(pl_test\test{{.pl:8):
8:        $i ++;
auto(-1)  DB<2> #

  DB<2>
main::(pl_test\test{{.pl:9):
9:        print "foo";
auto(-1)  DB<2> #

  DB<2>
foomain::(pl_test\test{{.pl:10):
10:       print " $i\n";
auto(-1)  DB<2> #

  DB<2>
 4
main::(pl_test\test{{.pl:8):
8:        $i ++;
auto(-1)  DB<2> #

  DB<2>
main::(pl_test\test{{.pl:9):
9:        print "foo";
auto(-1)  DB<2> #

  DB<2>
foomain::(pl_test\test{{.pl:10):
10:       print " $i\n";
auto(-1)  DB<2> #

  DB<2>
 5
main::(pl_test\test{{.pl:8):
8:        $i ++;
auto(-1)  DB<2> #

  DB<2>
main::(pl_test\test{{.pl:9):
9:        print "foo";
auto(-1)  DB<2> #

  DB<2>
foomain::(pl_test\test{{.pl:10):
10:       print " $i\n";
auto(-1)  DB<2> #

  DB<2>
 6
Debugged program terminated.  Use q to quit or R to restart,
  use o inhibit_exit to avoid stopping after program termination,
  h q, h R or h o to get additional info.
auto(-1)  DB<2> #

  DB<2>
Use `q' to quit or `R' to restart.  `h q' for details.
  DB<2> s
Use `q' to quit or `R' to restart.  `h q' for details.
  ...

WTF?

[almut]

BUT, stepping (entirely) through the script...

?? — I don't really see a difference in output. For example, the line print " $i\n" is still printing 3..6.  And the "foo" is there as well: foomain::(...

[incognito129]

I tried it out but it didn't work.