FAQ 3.5 How do I debug my Perl programs?

This message is one of several periodic postings to comp.lang.perl.misc
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------------------------------------------------------------ --------

3.5: How do I debug my Perl programs?

Have you tried "use warnings" or used "-w"? They enable warnings to
detect dubious practices.

Have you tried "use strict"? It prevents you from using symbolic
references, makes you predeclare any subroutines that you call as bare
words, and (probably most importantly) forces you to predeclare your
variables with "my", "our", or "use vars".

Did you check the return values of each and every system call? The
operating system (and thus Perl) tells you whether they worked, and if
not why.

open(FH, "> /etc/cantwrite")
or die "Couldn't write to /etc/cantwrite: $!\n";

Did you read perltrap? It's full of gotchas for old and new Perl
programmers and even has sections for those of you who are upgrading
from languages like *awk* and *C*.

Have you tried the Perl debugger, described in perldebug? You can step
through your program and see what it's doing and thus work out why what
it's doing isn't what it should be doing.



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Re: FAQ 3.5 How do I debug my Perl programs?

PerlFAQ Server schreef:
>
> 3.5: How do I debug my Perl programs?
>
> Have you tried "use warnings" or used "-w"? They enable warnings to
> detect dubious practices.
>
> Have you tried "use strict"? It prevents you from using symbolic
> references, makes you predeclare any subroutines that you call as bare
> words, and (probably most importantly) forces you to predeclare your
> variables with "my", "our", or "use vars".
>
> Did you check the return values of each and every system call? The
> operating system (and thus Perl) tells you whether they worked, and if
> not why.
>
> open(FH, "> /etc/cantwrite")
> or die "Couldn't write to /etc/cantwrite: $!\n";

In the light of recent posts about the three-argument form of open,
shouldn't this now be
open(FH, ">", "/etc/cantwrite")
or die "Couldn't write to /etc/cantwrite: $!\n";

> Did you read perltrap? It's full of gotchas for old and new Perl
> programmers and even has sections for those of you who are upgrading
> from languages like *awk* and *C*.
>
> Have you tried the Perl debugger, described in perldebug? You can step
> through your program and see what it's doing and thus work out why what
> it's doing isn't what it should be doing.
>
>
>


--
Hendrik Maryns

Interesting websites:
www.lieverleven.be (I cooperate)
www.eu04.com European Referendum Campaign
aouw.org The Art Of Urban Warfare

Re: FAQ 3.5 How do I debug my Perl programs?

In article <1112983116.655937@seven.kulnet.kuleuven.ac.be>, Hendrik
Maryns wrote:

> PerlFAQ Server schreef:

> > 3.5: How do I debug my Perl programs?

> > open(FH, "> /etc/cantwrite")
> > or die "Couldn't write to /etc/cantwrite: $!\n";

> In the light of recent posts about the three-argument form of open,
> shouldn't this now be

> open(FH, ">", "/etc/cantwrite")
> or die "Couldn't write to /etc/cantwrite: $!\n";

It could be that, but it doesn't need to be. The answer discussing
checking return values, and I think it does that just fine.

I'll keep this on my list of things to look at, but if I'm going
to change it to the three argument form, I'll go through every
open() in perlfaq and make them use it.

--
brian d foy, comdog@panix.com
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