Can't find any documentation on < a b c

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

Dear wise monks.
I have stumbled over a piece of code that uses a syntax like < a b c > to specify a list of values, like in

$ perl -we 'print "$_\n" for < a b c >;'
a
b
c
[download]

my $array_ref = [< 1 2 3 4 5 >];
[download]

Playing around with it a bit, I found out that even things like

use Data::Dump < pp >;
[download]

seem to work (as long as what is inside the angle brackets does not look too much like a file handle).

It seems like < ... > works a lot like qw(...) in that there are no commas needed to separate the parts, but also a bit like qq(...) (or plain "...") in that variables are substituted. Like in this example:

$ perl -we 'use Data::Dump < pp >; $x="foo"; pp <a 2 $x b>;'
("a", 2, "foo", "b")
[download]

I am wondering why I have never seen this syntax in any literature (or do I just get old and forget things?).
I would therefore like to ask for enlightenment about where to find any documentation about this syntax.
(A pointer to a relevant section of https://perldoc.perl.org/ would be much admired!).

Thank you for your help!

Comment on Can't find any documentation on < a b c > syntax for lists Select or Download Code

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Re: Can't find any documentation on < a b c > syntax for lists by kcott (Archbishop) on Feb 14, 2023 at 03:42 UTC
G'day muthm, Welcome to the Monastery. `$ perl -MO=Deparse,-p -e 'print "$_\n" for < a b c >;' use File::Glob (); print(("$_\n")) foreach (glob(' a b c ')); -e syntax OK` [download] Documentation for your admiration :-) File::Glob glob() perlop: I/O Operators — Ken	[reply] [d/l]
Re: Can't find any documentation on < a b c > syntax for lists by haukex (Archbishop) on Feb 14, 2023 at 07:19 UTC
See Creating arrays with glob patterns without metacharacters and my reply there, but also my node about glob having many caveats.	[reply]
Re: Can't find any documentation on < a b c > syntax for lists by jwkrahn (Abbot) on Feb 14, 2023 at 03:27 UTC
It's a file glob. It's looking for the files 'a', 'b' and 'c' and then returns that list. `perldoc -f glob` Naked blocks are fun! -- Randal L. Schwartz, Perl hacker	[reply]
Re^2: Can't find any documentation on < a b c > syntax for lists by ikegami (Patriarch) on Feb 14, 2023 at 05:38 UTC
`<a b c>` doesn't look for files. But `<[abc]>` and `<*>` would.	[reply] [d/l] [select]
Re^3: Can't find any documentation on < a b c > syntax for lists by Anonymous Monk on Feb 14, 2023 at 06:33 UTC
Why are these different? `perl -MO=Deparse,-p -e 'print "$_\n" for < a >;'` [download] use File::Glob (); print("$_\n") foreach (glob(' a ')); `perl -MO=Deparse,-p -e 'print "$_\n" for <a>;'` [download] print("$_\n") foreach (readline(a));	[reply] [d/l] [select]
Re^4: Can't find any documentation on < a b c > syntax for lists by Athanasius (Archbishop) on Feb 14, 2023 at 07:08 UTC
Re^4: Can't find any documentation on < a b c > syntax for lists by LanX (Saint) on Feb 14, 2023 at 14:33 UTC
Re^4: Can't find any documentation on < a b c > syntax for lists by ikegami (Patriarch) on Feb 14, 2023 at 15:38 UTC
Re^5: Can't find any documentation on < a b c > syntax for lists by Anonymous Monk on Feb 14, 2023 at 16:03 UTC
Some notes below your chosen depth have not been shown here
Re: Can't find any documentation on < a b c > syntax for lists by muthm (Sexton) on Feb 14, 2023 at 16:28 UTC
Thank you all, I have learned a lot! Mostly, that I will stick to `qw(...)` in the future. Safety first :-). My belief is strengthened!	[reply] [d/l]
Re^2: Can't find any documentation on < a b c > syntax for lists by kcott (Archbishop) on Feb 14, 2023 at 23:16 UTC
"Mostly, that I will stick to `qw(...)` in the future." Just be aware of this common mistake: `$ perl -we 'print "$_\n" for qw{ a b c };' a b c $ perl -we 'for qw{ a b c } { print "$_\n"; }' Missing $ on loop variable at -e line 1. $ perl -we 'for (qw{ a b c }) { print "$_\n"; }' a b c` [download] You can leave the parentheses off when `for` is used as a statement modifier; but not when it introduces a compound statement. See perlsyn for more about that. It's a common mistake because, although it was never really valid, Perl didn't report a problem until `v5.14.0`. For details, see: "perl5140delta: Use of qw(...) as parentheses" (warning - deprecated) "perl5180delta: qw(...) can no longer be used as parentheses" (error - disallowed) — Ken	[reply] [d/l] [select]