Where automatic variable $

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

To use FILEHANDLE alone to print the content of $_ to it, you must use a bareword filehandle like FH, not an indirect one like $fh

I saw some websites saying that BAREWORDS to refer file handles are dangerous because they are global. But now here I see they "prohibiting" it when you like a syntax sugar. Just don't get it...

Is there any other context where automatic use of $_ can't be applyed?

I mean, if I want to print the current $_ to another file handle (not STD{OUT,ERR, etc.) I can't omit $_:

while(<>){
print $fh; #doesn't work
print $fh $_; #work
}
[download]

Comment on Where automatic variable $_ doesn't work? Download Code

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Re: Where automatic variable $_ doesn't work? by choroba (Cardinal) on Jul 04, 2016 at 19:58 UTC
You can use select if sugar is so important: `select $fh; print while <>;` [download] ($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^2: Where automatic variable $_ doesn't work? by GrandFather (Saint) on Jul 04, 2016 at 20:55 UTC
However: `print $fh while <>;` [download] is both shorter and clearer. Update: Argh! that falls foul of the OP's complaint. It needs to be: `print $fh $_ while <>;` [download] to work as intended. Premature optimization is the root of all job security	[reply] [d/l] [select]
Re^3: Where automatic variable $_ doesn't work? by choroba (Cardinal) on Jul 04, 2016 at 21:12 UTC
Although its output is quite different. ($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]
Re^2: Where automatic variable $_ doesn't work? by guiwp (Sexton) on Jul 04, 2016 at 20:27 UTC
I didn't known about select, Thank you! "if sugar is so important" When it's possible, I do like =)	[reply]
Re: Where automatic variable $_ doesn't work? by haukex (Archbishop) on Jul 04, 2016 at 20:04 UTC
Hi guiwp, It's not "prohibited": How should Perl tell the difference between `print $fh;` and `print $fh;`? With the first one I meant "print the value of `$fh` to the currently selected filehandle" and with the second one I meant "print `$_` to the filehandle `$fh`"? That's taking DWIM a little too far ;-) Regards, -- Hauke D	[reply] [d/l] [select]
Re^2: Where automatic variable $_ doesn't work? by guiwp (Sexton) on Jul 04, 2016 at 20:23 UTC
I always thought Perl was taking DWIM a little too far! I assume the compiler (and the human that made it!) is pretty smart =) Thank you @haukex	[reply]