print source golf

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

Dear Monks, I was golfing around with ways to make perl print its own source and came up with something odd. I would expect the following program to print the first line of itself but it prints the entire file. Why does it do that?

#!/usr/bin/perl

use strict;
use warnings;

print do{@ARGV=$0;<>};
[download]

My path thru this course:

print do{local(@ARGV,$/)=$0;<>}; # the usual idiom
print do{@ARGV=$0;local$/;<>};
print do{@ARGV=$0;$/='';<>};     # bad
print do{open$_,"<$0";<$_>};
print do{@ARGV=$0;*/;<>};        # wtf
print do{@ARGV=$0;<>};           # wow
[download]

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Re: print source golf by LanX (Saint) on Oct 14, 2019 at 16:17 UTC
> Why does it do that? `readline` in list context. FWIW `use strict; use warnings; seek DATA,0,0; print scalar <DATA>; __DATA__` [download] prints `use strict;` Cheers Rolf _{(addicted to the Perl Programming Language :) Wikisyntax for the Monastery FootballPerl is like chess, only without the dice}	[reply] [d/l] [select]
Re: print source golf by Corion (Patriarch) on Oct 14, 2019 at 16:21 UTC
How about this? `#!perl open 0;print for<0>;` [download] This takes advantage of Single-argument open opens a filehandle `X` using the value stored in `$X` as the filename. Since `$0` contains the filename of our program, `0` will be opened as our filehandle. `print for<0>;` reads from filehandle `*0` and prints the content.	[reply] [d/l] [select]
Re^2: print source golf by tobyink (Canon) on Oct 14, 2019 at 21:10 UTC
You don't really need the `for`. `#!perl open+0;print<0>` [download] toby döt ink	[reply] [d/l] [select]
Re: print source golf by tybalt89 (Monsignor) on Oct 14, 2019 at 16:07 UTC
`print do{@ARGV=$0;scalar<>};` [download] Or `print do{@ARGV=$0;~~<>};` [download]	[reply] [d/l] [select]
Re: print source golf by daxim (Curate) on Oct 14, 2019 at 17:24 UTC
`print do{@ARGV=$0;/;<>}; # wtf` [download] `/` is the glob for the family of variables named `/`, short for `*main::/`. Perl core uses `$/`. Regexp::Grammars uses `%/`.	[reply] [d/l] [select]
Re: print source golf by davido (Cardinal) on Oct 15, 2019 at 15:43 UTC
Is it cheating to use the shell? `#!/usr/bin/perl exec"cat $0"` [download] If you're ok with letting the output happen on STDERR instead of STDOUT: #!/usr/bin/perl die`cat $0` [download] ...which shaves off one keystroke. Dave	[reply] [d/l] [select]