390 diagnostic warnings, deprecations, errors in perl 5.002b3 Feb 03, 1996: 
perl -MHTTP::Tiny -le'$|++;for(split/\n/,HTTP::Tiny->new->get("https:/
+/fastapi.metacpan.org/source/LWALL/perl5.002b3/pod/perldiag.pod")->{c
+ontent}){print${1}and$-++if/^=item\s+(\S\S.*)$/}print(($-+1)," diagno
+stic warnings, deprecations, errors in perl 5.002b3 Feb 03, 1996")'

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1104 diagnostic warnings, deprecations, errors in perl v5.42.0 Compiled at Dec 17 2025: 
perl -MConfig=compile_date -le'$|++;for(`perldoc -u perldiag`){print${
+1}and$-++if/^=item\s+(\S\S.*)$/}print(($-+1)," diagnostic warnings, d
+eprecations, errors in perl $^V ").compile_date()'

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What is forbidden? 
perl -MConfig=compile_date -le'$|++;for(`perldoc -u perldiag`){print${
+1}and$-++if/^=item\s+(\S\S.*)$/}print(($-+1)," diagnostic warnings, d
+eprecations, errors in perl $^V ").compile_date()' | grep 'forbidden'

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Experimental %s on scalar is now forbidden
Initialization of state variables in list currently forbidden
Setting $/ to a reference to %s is forbidden
Setting $/ to %s reference is forbidden
Use of bare << to mean <<"" is forbidden
Use of strings with code points over 0xFF as arguments to vec is forbidden

Replies are listed 'Best First'.
Re: diagnostics: warning, deprecation, error
by ikegami (Patriarch) on Feb 10, 2026 at 14:43 UTC

    All of these diagnostics are explained in perldiag.

    Experimental %s on scalar is now forbidden 
    $ perl -e'my $x = { }; keys $x;'
Experimental keys on scalar is now forbidden at -e line 1.
Type of arg 1 to keys must be hash or array (not private variable) at 
+-e line 1, at EOF
Execution of -e aborted due to compilation errors.

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    Bad operand type, but it was once accepted by an experimental feature.

    Initialization of state variables in list currently forbidden 
    $ perl -e'use feature qw( state ); ( state $x ) = 123;'
Initialization of state variables in list currently forbidden at -e li
+ne 1, near "123;"
Execution of -e aborted due to compilation errors.

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    $ perl -e'use feature qw( state ); state( $x ) = 123;'
Initialization of state variables in list currently forbidden at -e li
+ne 1, near "123;"
Execution of -e aborted due to compilation errors.

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    Never supported.

    Setting $/ to a reference to %s is forbidden 
    $ perl -e'$/ = \0;'
Setting $/ to a reference to zero is forbidden at -e line 1.

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    Bad data.

    Setting $/ to %s reference is forbidden 
    $ perl -e'$/ = { };'
Setting $/ to a HASH reference is forbidden at -e line 1.

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    Bad data.

    Use of bare << to mean <<"" is forbidden 
    $ perl
my $x = <<.
Use of bare << to mean <<"" is forbidden at - line 1.

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    Bad syntax. Non-word terminators must be quoted.

    Use of strings with code points over 0xFF as arguments to vec is forbidden 
    $ perl -e'my $x = chr( 0x2660 ); vec( $x, 0, 1 );'
Use of strings with code points over 0xFF as arguments to vec is forbi
+dden at -e line 1.

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    Bad data. This is basically a friendly version of "Wide character in %s".

[reply]
[d/l]
[select]

      no longer supported

      perl -MConfig=compile_date -le'$|++;for(`perldoc -u perldiag`){print${
+1}and$-++if/^=item\s+(\S\S.*)$/}print(($-+1)," diagnostic warnings, d
+eprecations, errors in perl $^V ").compile_date()' | grep -i 'no long
+er supported'

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      \C no longer supported in regex; marked by S<<-- HERE> in m/%s/
${^ENCODING} is no longer supported
$* is no longer supported as of Perl 5.30
$# is no longer supported as of Perl 5.30

      did you mean

      perl -MConfig=compile_date -le'$|++;for(`perldoc -u perldiag`){print${
+1}and$-++if/^=item\s+(\S\S.*)$/}print(($-+1)," diagnostic warnings, d
+eprecations, errors in perl $^V ").compile_date()' | grep -i 'did you
+ mean'

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      (Did you mean &%s instead?)
(Did you mean "local" instead of "our"?)
(Did you mean $ or @ instead of %?)
do "%s" failed, '.' is no longer in @INC; did you mean do "./%s"?
length() used on %s (did you mean "scalar(%s)"?)
Perl %s required (did you mean %s?)--this is only %s, stopped
$[ used in %s (did you mean $] ?)

      crash

      perl -MConfig=compile_date -le'$|++;for(`perldoc -u perldiag`){print${
+1}and$-++if/^=item\s+(\S\S.*)$/}print(($-+1)," diagnostic warnings, d
+eprecations, errors in perl $^V ").compile_date()' | grep -i crash

      [download]
      Locale '%s' is unsupported, and may crash the interpreter
[reply]
[d/l]
[select]

        Do you have a point or a question?

[reply]

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