Re: escaping the @ in an interpolating string

@$0 is seen as @{ $0 }, which takes $0 as a symbolic reference to the array named -e:

perl -e '@{q(-e)} = qw(Hello World); print "$0: @$0\n"'
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-e: Hello World
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If you enable strict, symbolic references are disallowed though:

perl -Mstrict -e '@{q(-e)} = qw(Hello World); print "$0: @$0\n"'

Can't use string ("-e") as an ARRAY ref while "strict refs" in use at 
+-e line 1.
[download]

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Re^2: escaping the @ in an interpolating string by Danny (Chaplain) on Aug 10, 2024 at 18:56 UTC
Also, if you are unsure what $0 means see 'perldoc perlvar' and search for $0.	[reply]
Re^3: escaping the @ in an interpolating string by marto (Cardinal) on Aug 10, 2024 at 19:27 UTC
Or `perldoc -v '$0'` See also: perldoc	[reply] [d/l]
Re^2: escaping the @ in an interpolating string by raygun (Scribe) on Aug 10, 2024 at 18:51 UTC
I guess I should have been less specific! @$0 is seen as @{ $0 } The issue isn't limited to $0 following the @: no matter what variable follows it—whether it exists or not—the @ is not interpreted literally. `$ perl -e 'print "@$$\n";' $ perl -e 'print "@$undefined_variable\n";' $ perl -e 'print "@$]\n";' ] $ perl -e 'print "@$(\n";' (` [download] Interestingly, sometimes the entire `@$foo` seems to be interpreted as a unit, printing nothing, and other times `@$` seems to be interpreted as one unit, printing whatever follows it literally. In no case is the @ interpreted literally. And, of course, in all cases preceding the @ with a backslash solves that, and allows the following variable to be interpolated: `$ perl -e 'print "\@$$\n";' @24477 $ perl -e 'print "\@$undefined_variable\n";' @ $ perl -e 'print "\@$]\n";' @5.030003 $ perl -e 'print "\@$(\n";' @500 7 10 11 16 18 19 27 35 80 85 100 105 500` [download]	[reply] [d/l] [select]
Re^3: escaping the @ in an interpolating string by Danny (Chaplain) on Aug 10, 2024 at 19:11 UTC
Those are all doing the same thing that Corion explained. They are inferring that $$, $undefined_variable etc are symbolic references to an array. If you 'use strict' it will give an error. Without 'use strict' you can do something like: `perl -e '@hi = (1,2,3), my $x = "hi"; print "@$x\n";'` [download] and it will output: `1 2 3` [download]	[reply] [d/l] [select]
Re^4: escaping the @ in an interpolating string by raygun (Scribe) on Aug 10, 2024 at 19:23 UTC
Ah, it would've helped if I hadn't misread Corion's explanation. Yours managed to penetrate my thick skull. Thank you!	[reply]
Re^3: escaping the @ in an interpolating string by NERDVANA (Priest) on Aug 10, 2024 at 19:42 UTC
More to the point, `@$foo` is perfectly useful syntax even with strict enabled: `use strict; use warnings; my $foo= [ 1, 2, 3 ]; for (@$foo) { say $_ }` [download]	[reply] [d/l] [select]
Re^3: escaping the @ in an interpolating string by japhy (Canon) on Aug 13, 2024 at 02:33 UTC
In the case of those punctuation variables (e.g. `$]` and `$(`), Perl interprets `"@$]"` as `"@$"` and `"]"`, and since `@$` is empty, you get nothing, followed by the punctuation character. Jeffrey Pinyan (TypeScript, JavaScript, PHP, Perl; in that order nowadays) @JeffPinyan — @NightSkyJeff Melius servire volo	[reply] [d/l] [select]
Re^4: escaping the @ in an interpolating string by raygun (Scribe) on Aug 13, 2024 at 10:00 UTC
Yeah, I could deduce from the output that it was doing that, but initially I couldn't figure out why it would parse those two differently from the others. But with the light shed by Corion and Danny, I figured it out: `$]` and `$(` expand into things that aren't legal variable names. So perl must, upon noticing that, deduce that a symbolic reference is not what it's seeing, and fall back on the alternate parsing you mention.	[reply] [d/l] [select]