Re^4: Using IO::CaptureOutput in a child process to caputre STDOUT and STDERR

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Re^5: Using IO::CaptureOutput in a child process to caputre STDOUT and STDERR by Anonymous Monk on Apr 10, 2011 at 23:18 UTC
There is no "&" address of this constant value defined. Um, in perl, & is not the address-of operator `$ perl -MPOSIX=WNOHANG -e "print WNOHANG, &WNOHANG" 11` [download]	[reply] [d/l]
Re^6: Using IO::CaptureOutput in a child process to caputre STDOUT and STDERR by Marshall (Canon) on Apr 11, 2011 at 06:03 UTC
My comment was not right. ~~See better explanation below.~~ ~~&WNOHANG is a deprecated syntax, but still works.~~ Yes, & is Perl bitwise operator. I consider it bad form to "AND" a constant with itself. Omit the &. Update: As a matter of style, I would omit the & in front of WNOHANG. In 'C' that is the way that is is done. I am surprised that you can put & in front of WNOHANG, but ok it is obviously true that in Perl you can. Do as you will, I would not put that & there.	[reply]
Re^7: Using IO::CaptureOutput in a child process to caputre STDOUT and STDERR by Eliya (Vicar) on Apr 11, 2011 at 07:45 UTC
While I agree the `&` isn't needed here, it's not the bitwise operator in this case. That would require two operands — to bitwise "and" something with itself you'd have to write e.g. `42 & 42`. Rather, the `&` here is the subroutine sigil. While it was required in the early days of Perl, it's optional these days, and its use is discouraged except for special purposes, such as to take a reference of a subroutine (`\&foo`), or to circumvent prototypes (see perlsub). And the latter is also the reason you shouldn't use `&` with constants: constants are subroutines with an empty prototype, which makes Perl optimize the function call away. Telling Perl to circumvent the prototype is not a good idea as it prevents the optimization: $ perl -MO=Concise -e 'sub foo(){42}; print foo' 6 <@> leave[1 ref] vKP/REFC ->(end) 1 <0> enter ->2 2 <;> nextstate(main 2 -e:1) v:{ ->3 5 <@> print vK ->6 3 <0> pushmark s ->4 4 <$> const[IV 42] s ->5 -e syntax OK $ perl -MO=Concise -e 'sub foo(){42}; print &foo' 8 <@> leave[1 ref] vKP/REFC ->(end) 1 <0> enter ->2 2 <;> nextstate(main 2 -e:1) v:{ ->3 7 <@> print vK ->8 3 <0> pushmark s ->4 6 <1> entersub[t2] lK/TARG,AMPER,1 ->7 - <1> ex-list lK ->6 4 <0> pushmark s ->5 - <1> ex-rv2cv sK/8 ->- 5 <#> gv[*foo] s ->6 -e syntax OK [download]	[reply] [d/l] [select]
Re^8: Using IO::CaptureOutput in a child process to caputre STDOUT and STDERR by Marshall (Canon) on Apr 13, 2011 at 07:54 UTC
Re^7: Using IO::CaptureOutput in a child process to caputre STDOUT and STDERR by Anonymous Monk on Apr 15, 2011 at 20:39 UTC
&WNOHANG is a deprecated syntax, but still works. Actually no, it is not a deprecated syntax as of perl v5.14.0	[reply]
Re^7: Using IO::CaptureOutput in a child process to caputre STDOUT and STDERR by Anonymous Monk on Apr 12, 2011 at 06:20 UTC
Yes, & is Perl bitwise operator. I consider it bad form to "AND" a constant with itself. Omit the &. FWIW, doing/advising something without understanding the reasons is called cargo-culting. As Eliya eloquently explained, bad style is not the same as wrong syntax :)	[reply]