How to skip a step in perldebug?

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

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Re: How to skip a step in perldebug? by casiano (Pilgrim) on Aug 07, 2008 at 08:37 UTC
You can skip some code if you label the target statement as illustrated in the following example: pp2@nereida:~/Ltesting$ perl -wd skipdeb.pl Loading DB routines from perl5db.pl version 1.28 Editor support available. Enter h or `h h' for help, or `man perldebug' for more help. main::(skipdeb.pl:2): my $a = 4; DB<1> l 2==> my $a = 4; 3: my $b = 4; 4: my $c = 4; 5 6: $a = 5; 7: $a += 1; 8: L:$a = $c$a; 9: $a = $c$b; 10: print "$a\n"; DB<1> c 6 main::(skipdeb.pl:6): $a = 5; DB<2> b 9 DB<3> goto L main::(skipdeb.pl:9): $a = $c*$b; DB<4> p $a 16 [download] The value of `$a` is 16. We have skipped statements 6 and 7. Hope it helps Casiano	[reply] [d/l] [select]
Re^2: How to skip a step in perldebug? by repellent (Priest) on Aug 07, 2008 at 21:17 UTC
Casiano, thanks for replying. I'm afraid that this approach is slightly lacking: If I knew enough to place a label where I would like to skip, I might as well have commented the skipped line(s) out. It would be nice to dynamically decide which code executions to skip, after running `perl -d` only once. What would work is a `goto [line_number]`.	[reply] [d/l] [select]
Re: How to skip a step in perldebug? by casiano (Pilgrim) on Aug 07, 2008 at 09:04 UTC
Regarding your second question would it be possible to dynamically modify a line statement via the interactive debugger? I also don't know. What I do is the same trick that in the previous solution but before the `goto L` I do the "substituting" statement like in: pp2@nereida:~/Ltesting$ perl -wd skipdeb.pl Loading DB routines from perl5db.pl version 1.28 Editor support available. Enter h or `h h' for help, or `man perldebug' for more help. main::(skipdeb.pl:2): my $a = 4; DB<1> l 2==> my $a = 4; 3: my $b = 4; 4: my $c = 4; 5 6: $a = 5; 7: $a += 1; 8: L:$a = $c$a; 9: $a = $c$b; 10: print "$a\n"; DB<1> c 6 main::(skipdeb.pl:6): $a = 5; DB<2> b 9 DB<3> $a = 8 # This statement substitutes the skipped ones DB<4> goto L main::(skipdeb.pl:9): $a = $c*$b; DB<5> p $a 32 [download]	[reply] [d/l] [select]
Re^2: How to skip a step in perldebug? by repellent (Priest) on Aug 07, 2008 at 21:28 UTC
Yes, skipping & entering your own code expression instead is akin to modifying the line statement. I was also wondering about issues like breaking scope, etc. Here's a made-up example: `1: while (<STDIN>) { 2: push(@F, $_); 3==> shift(@F) if $. > 10; 4 }` [download] I wish to replace `line 3` with `shift(@F) if $. > 10; }{ print @F;` [download] instead. This modification still results in valid code. How far can we push this?	[reply] [d/l] [select]