Preventing Use of uninitialized value.

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

Replies are listed 'Best First'.
Re: Preventing Use of uninitialized value. by 1nickt (Canon) on Dec 12, 2018 at 18:58 UTC
Don't test for a match if there is no line: `if (defined $line and $line =~ /(\bTest\b\s+.+\s+\baccount\b)?/)` [download] `if ( ($line // '') =~ /(\bTest\b\s+.+\s+\baccount\b)?/)` [download] (Update: added parens to handle precedence of `//`, thx to choroba) Hope this helps! The way forward always starts with a minimal test.	[reply] [d/l] [select]
Re^2: Preventing Use of uninitialized value. by choroba (Cardinal) on Dec 13, 2018 at 17:05 UTC
Unfortunately, // has a different precedence: `if (($line // '') =~ /(\bTest\b\s+.+\s+\baccount\b)?/)` [download] Easy to verify with B::Deparse: `$ perl -MO=Deparse,-p -e 'if ($line // "" =~ /(\bTest\b\s+.+\s+\baccou +nt\b)?/) {}' if (($line // ('' =~ /(\bTest\b\s+.+\s+\baccount\b)?/))) { (); } -e syntax OK` [download] ($q=q:Sq=~/;[c](.)(.)/;chr(-\|\|-\|5+lengthSq)`"S\|oS2"`map{chr \|+ord }map{substrSq`S_+\|`\|}3E\|-\|`7**2-3:)=~y+S\|`+$1,++print+eval$q,q,a, [download]	[reply] [d/l] [select]
Re^3: Preventing Use of uninitialized value. by 1nickt (Canon) on Dec 13, 2018 at 18:27 UTC
Yep! As you were writing that I was composing another reply in which I discovered that fact. Thanks for the correction. The way forward always starts with a minimal test.	[reply]
Re: Preventing Use of uninitialized value. by Laurent_R (Canon) on Dec 12, 2018 at 23:37 UTC
At the very least, check for the file size before reading it.	[reply]
Re: Preventing Use of uninitialized value. by hippo (Archbishop) on Dec 12, 2018 at 23:49 UTC
It rather depends what you want your code to do instead. Since you are happy for it to die if you can't tail it then let's carry on throwing those exceptions. `die "File $log isn't long enough to process\n" unless defined $line;` [download]	[reply] [d/l]
Re: Preventing Use of uninitialized value. by tobyink (Canon) on Dec 12, 2018 at 21:27 UTC
`use strict; use warnings; no warnings qw(void once uninitialized); # the annoying warnings` [download] toby döt ink	[reply] [d/l]
Re^2: Preventing Use of uninitialized value. by stevieb (Canon) on Dec 12, 2018 at 22:23 UTC
Hey tobyink, it does rectify the OPs question, but it appears as though you may be being a bit facetious here. Yeah?	[reply]
Re^3: Preventing Use of uninitialized value. by tobyink (Canon) on Dec 13, 2018 at 09:13 UTC
Not really. Those warnings annoy me. The ability to treat an uninitialized variable as zero or the empty string is handy and is part of what makes perl Perl. Explicitly having to check whether a variable is undef at runtime makes code unnecessarily verbose and (very slightly) slower. I can understand wanting to have this warning available to help people with debugging, but 99% of the time, it's annoying. I don't think the `once` or `void` warnings categories have ever helped me find a real error in my code. `once` becomes annoying if you want to do things like: `printf "%s%s\n", $MyModule::Config::Indent ? "\t" : "", $output;` [download] Where `$MyModule::Config::Indent` is a variable that end users can set to true if they want indented output. That might be the only place in my module where I perform any output, so that variable would only be referenced once. I don't want a warning for that. (And yes, I know globals are bad in general, but there are some places where their use can be expedient.) The `numeric` warnings category can be annoying at times too, but it's just helpful enough for me to want to keep it enabled most of the time. toby döt ink	[reply] [d/l] [select]
Re^4: Preventing Use of uninitialized value. by 1nickt (Canon) on Dec 13, 2018 at 18:26 UTC