Where did all the time go?

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

Just seeking enlightenment here. Already can get it to do what I want, but... I was typing in a few things to get them in the exact format I wanted when I ran into a peculiarity. When I enter

perl -e '($s,$m,$h,$md,$mo,$y,$w,$g,$i)=localtime;print $y+1900 . "." . ($mo+1) . ".$md." . ($h-5) . "$m\n";'

I get 2019.8.1.19.47. (I hope I transcribed the above correctly)

But if I type

perl -e '($s,$m,$h,$md,$mo,$y,$w,$g,$i)=localtime;print $y+1900 . "." . $mo+1 . ".$md." . ($h-5) . "$m\n";'

I get 2020.7.1.19.47. The +1 after $mo now gets applied to $y instead. The same is true for the parentheses around $h. I am trying to wrap my feeble mind around this one. What is going on?

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Re: Where did all the time go? by choroba (Cardinal) on Aug 01, 2019 at 20:20 UTC
Precedence issue. Use B::Deparse with `-p` to see how Perl interprets the code: $ perl -MO=Deparse,-p -e '($s,$m,$h,$md,$mo,$y,$w,$g,$i)=localtime;pri +nt $y+1900 . "." . ($mo+1) . ".$md." . ($h-5) . "$m\n";' (($s, $m, $h, $md, $mo, $y, $w, $g, $i) = (localtime)); print((((((($y + 1900) . '.') . ($mo + 1)) . ".$md.") . ($h - 5)) . "$ +m\n")); $ perl -MO=Deparse,-p -e '($s,$m,$h,$md,$mo,$y,$w,$g,$i)=localtime;pri +nt $y+1900 . "." . $mo+1 . ".$md." . ($h-5) . "$m\n";' (($s, $m, $h, $md, $mo, $y, $w, $g, $i) = (localtime)); print(((((((($y + 1900) . '.') . $mo) + 1) . ".$md.") . ($h - 5)) . "$ +m\n")); [download] `map{substr$_->[0],$_->[1]\|\|0,1}[\\|\|{},3],[[]],[ref qr-1,-,-1],[{}],[sub{}^ARGV,3]`	[reply] [d/l] [select]
Re^2: Where did all the time go? by ExReg (Priest) on Aug 01, 2019 at 20:29 UTC
I knew it had to be precedence, but was unsure what it really looked like. The B::Deparse showed it beautifully. I will have to remember that one.	[reply]
Re: Where did all the time go? by Fletch (Bishop) on Aug 01, 2019 at 20:20 UTC
Tangential, but you might look at POSIX and `strftime` or something like DateTime::Format rather than monkeying with reimplementing wheels. As to your question you can see how the precedence changes omitting the parens plays out if you stick `-MO=Deparse,-p` before the `-e`. Update: Yeah, what he said below. The cake is a lie. The cake is a lie. The cake is a lie.	[reply] [d/l] [select]
Re^2: Where did all the time go? by haukex (Archbishop) on Aug 01, 2019 at 20:32 UTC
POSIX and `strftime` I'd suggest Time::Piece instead, it's been a core module since 5.10. `<update>` `$ perl -MTime::Piece -le 'print localtime->strftime("%Y.%m.%d.%H%M")' 2019.08.01.2239` [download] `</update>` DateTime::Format Note that link goes to a defunct module, you probably meant the `DateTime::Format::*` family of modules instead. But plain DateTime has both `strftime` and CLDR formatting built right in, that's generally been enough for me (I usually parse with DateTime::Format::Strptime).	[reply] [d/l] [select]