in reply to diagnostics: warning, deprecation, error

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.

[download]

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.

[download]
$ 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.

[download]

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.

[download]

Bad data.

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

[download]

Bad data.

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

[download]

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.

[download]

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

Replies are listed 'Best First'.
Re^2: diagnostics: warning, deprecation, error
by Anonymous Monk on Feb 10, 2026 at 16:01 UTC

    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'

    [download]
    \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'

    [download]
    (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]
        Usual perl error: 
        perl -MSuper::Duper -e 'print Super::Duper->new->thing'

        [download]
        Can't locate Super/Duper.pm in @INC (you may need to install the Super::Duper module) (@INC entries checked: /Users/u/perl5/perlbrew/perls/perl-5.42.0/lib/site_perl/5.42.0/darwin-2level /Users/u/perl5/perlbrew/perls/perl-5.42.0/lib/site_perl/5.42.0 /Users/u/perl5/perlbrew/perls/perl-5.42.0/lib/5.42.0/darwin-2level /Users/u/perl5/perlbrew/perls/perl-5.42.0/lib/5.42.0).
BEGIN failed--compilation aborted.
        Improved perl error: 
        perl -MIPC::Cmd=run -le '@_=run(command=>"perl -MSuper::Duper");$_=joi
+n"",@{$_[2]};s/ ([\(])/\n/g;s/ ([\/])/\n $1/g;s/\)//g;chomp;print'

        [download]
        Can't locate Super/Duper.pm in @INC
you may need to install the Super::Duper module
@INC entries checked:
 /Users/u/perl5/perlbrew/perls/perl-5.42.0/lib/site_perl/5.42.0/darwin-2level
 /Users/u/perl5/perlbrew/perls/perl-5.42.0/lib/site_perl/5.42.0
 /Users/u/perl5/perlbrew/perls/perl-5.42.0/lib/5.42.0/darwin-2level
 /Users/u/perl5/perlbrew/perls/perl-5.42.0/lib/5.42.0.
BEGIN failed--compilation aborted.
        Ideal perl error? (formatted nice like perl -v): 
        Can't locate Super/Duper.pm in @INC
See: perldoc -v @INC

You may need to install the Super::Duper module!
https://metacpan.org/search?q=Super::Duper

@INC entries checked:
 /Users/u/perl5/perlbrew/perls/perl-5.42.0/lib/site_perl/5.42.0/darwin-2level
 /Users/u/perl5/perlbrew/perls/perl-5.42.0/lib/site_perl/5.42.0
 /Users/u/perl5/perlbrew/perls/perl-5.42.0/lib/5.42.0/darwin-2level
 /Users/u/perl5/perlbrew/perls/perl-5.42.0/lib/5.42.0.

BEGIN failed--compilation aborted.
[reply]
[d/l]
[select]

In Section Meditations