Re: [perl #18048] read \*FH, ... returns undef but doesn' t set $! if \*FH not open

[p5sagit/p5-mst-13.2.git] / pod / perldiag.pod

=head1 NAME

perldiag - various Perl diagnostics

=head1 DESCRIPTION

These messages are classified as follows (listed in increasing order of
desperation):

    (W) A warning (optional).
    (D) A deprecation (optional).
    (S) A severe warning (default).
    (F) A fatal error (trappable).
    (P) An internal error you should never see (trappable).
    (X) A very fatal error (nontrappable).
    (A) An alien error message (not generated by Perl).

The majority of messages from the first three classifications above
(W, D & S) can be controlled using the C<warnings> pragma.

If a message can be controlled by the C<warnings> pragma, its warning
category is included with the classification letter in the description
below.

Optional warnings are enabled by using the C<warnings> pragma or the B<-w>
and B<-W> switches. Warnings may be captured by setting C<$SIG{__WARN__}>
to a reference to a routine that will be called on each warning instead
of printing it.  See L<perlvar>.

Default warnings are always enabled unless they are explicitly disabled
with the C<warnings> pragma or the B<-X> switch.

Trappable errors may be trapped using the eval operator.  See
L<perlfunc/eval>.  In almost all cases, warnings may be selectively
disabled or promoted to fatal errors using the C<warnings> pragma.
See L<warnings>.

The messages are in alphabetical order, without regard to upper or
lower-case.  Some of these messages are generic.  Spots that vary are
denoted with a %s or other printf-style escape.  These escapes are
ignored by the alphabetical order, as are all characters other than
letters.  To look up your message, just ignore anything that is not a
letter.

=over 4

=item A thread exited while %d other threads were still running

(W) When using threaded Perl, a thread (not necessarily the main
thread) exited while there were still other threads running.
Usually it's a good idea to first collect the return values of the
created threads by joining them, and only then exit from the main
thread.  See L<threads>.

=item accept() on closed socket %s

(W closed) You tried to do an accept on a closed socket.  Did you forget
to check the return value of your socket() call?  See
L<perlfunc/accept>.

=item Allocation too large: %lx

(X) You can't allocate more than 64K on an MS-DOS machine.

=item '!' allowed only after types %s

(F) The '!' is allowed in pack() and unpack() only after certain types.
See L<perlfunc/pack>.

=item Ambiguous call resolved as CORE::%s(), qualify as such or use &

(W ambiguous) A subroutine you have declared has the same name as a Perl
keyword, and you have used the name without qualification for calling
one or the other.  Perl decided to call the builtin because the
subroutine is not imported.

To force interpretation as a subroutine call, either put an ampersand
before the subroutine name, or qualify the name with its package.
Alternatively, you can import the subroutine (or pretend that it's
imported with the C<use subs> pragma).

To silently interpret it as the Perl operator, use the C<CORE::> prefix
on the operator (e.g. C<CORE::log($x)>) or declare the subroutine
to be an object method (see L<perlsub/"Subroutine Attributes"> or
L<attributes>).

=item Ambiguous range in transliteration operator

(F) You wrote something like C<tr/a-z-0//> which doesn't mean anything at
all.  To include a C<-> character in a transliteration, put it either
first or last.  (In the past, C<tr/a-z-0//> was synonymous with
C<tr/a-y//>, which was probably not what you would have expected.)

=item Ambiguous use of %s resolved as %s

(W ambiguous)(S) You said something that may not be interpreted the way
you thought.  Normally it's pretty easy to disambiguate it by supplying
a missing quote, operator, parenthesis pair or declaration.

=item '|' and '<' may not both be specified on command line

(F) An error peculiar to VMS.  Perl does its own command line
redirection, and found that STDIN was a pipe, and that you also tried to
redirect STDIN using '<'.  Only one STDIN stream to a customer, please.

=item '|' and '>' may not both be specified on command line

(F) An error peculiar to VMS.  Perl does its own command line
redirection, and thinks you tried to redirect stdout both to a file and
into a pipe to another command.  You need to choose one or the other,
though nothing's stopping you from piping into a program or Perl script
which 'splits' output into two streams, such as

    open(OUT,">$ARGV[0]") or die "Can't write to $ARGV[0]: $!";
    while (<STDIN>) {
        print;
        print OUT;
    }
    close OUT;

=item Applying %s to %s will act on scalar(%s)

(W misc) The pattern match (C<//>), substitution (C<s///>), and
transliteration (C<tr///>) operators work on scalar values.  If you apply
one of them to an array or a hash, it will convert the array or hash to
a scalar value -- the length of an array, or the population info of a
hash -- and then work on that scalar value.  This is probably not what
you meant to do.  See L<perlfunc/grep> and L<perlfunc/map> for
alternatives.

=item Args must match #! line

(F) The setuid emulator requires that the arguments Perl was invoked
with match the arguments specified on the #! line.  Since some systems
impose a one-argument limit on the #! line, try combining switches;
for example, turn C<-w -U> into C<-wU>.

=item Arg too short for msgsnd

(F) msgsnd() requires a string at least as long as sizeof(long).

=item %s argument is not a HASH or ARRAY element

(F) The argument to exists() must be a hash or array element, such as:

    $foo{$bar}
    $ref->{"susie"}[12]

=item %s argument is not a HASH or ARRAY element or slice

(F) The argument to delete() must be either a hash or array element,
such as:

    $foo{$bar}
    $ref->{"susie"}[12]

or a hash or array slice, such as:

    @foo[$bar, $baz, $xyzzy]
    @{$ref->[12]}{"susie", "queue"}

=item %s argument is not a subroutine name

(F) The argument to exists() for C<exists &sub> must be a subroutine
name, and not a subroutine call.  C<exists &sub()> will generate this
error.

=item '%s' trapped by operation mask

(F) You tried to use an operator from a Safe compartment in which it's
disallowed. See L<Safe>.

=item Argument "%s" isn't numeric%s

(W numeric) The indicated string was fed as an argument to an operator
that expected a numeric value instead.  If you're fortunate the message
will identify which operator was so unfortunate.

=item Array @%s missing the @ in argument %d of %s()

(D deprecated) Really old Perl let you omit the @ on array names in some
spots.  This is now heavily deprecated.

=item assertion botched: %s

(P) The malloc package that comes with Perl had an internal failure.

=item Assertion failed: file "%s"

(P) A general assertion failed.  The file in question must be examined.

=item Assignment to both a list and a scalar

(F) If you assign to a conditional operator, the 2nd and 3rd arguments
must either both be scalars or both be lists.  Otherwise Perl won't
know which context to supply to the right side.

=item Attempt to access disallowed key '%s' in a restricted hash

(F) The failing code has attempted to get or set a key which is not in
the current set of allowed keys of a restricted hash.

=item Attempt to clear a restricted hash

(F) It is currently not allowed to clear a restricted hash, even if the
new hash would contain the same keys as before.  This may change in
the future.

=item Attempt to delete readonly key '%s' from a restricted hash

(F) The failing code attempted to delete a key whose value has been
declared readonly from a restricted hash.

=item Attempt to delete disallowed key '%s' from a restricted hash

(F) The failing code attempted to delete from a restricted hash a key
which is not in its key set.

=item Attempt to bless into a reference

(F) The CLASSNAME argument to the bless() operator is expected to be
the name of the package to bless the resulting object into. You've
supplied instead a reference to something: perhaps you wrote

    bless $self, $proto;

when you intended

    bless $self, ref($proto) || $proto;

If you actually want to bless into the stringified version
of the reference supplied, you need to stringify it yourself, for
example by:

    bless $self, "$proto";

=item Attempt to free non-arena SV: 0x%lx

(P internal) All SV objects are supposed to be allocated from arenas
that will be garbage collected on exit.  An SV was discovered to be
outside any of those arenas.

=item Attempt to free nonexistent shared string

(P internal) Perl maintains a reference counted internal table of
strings to optimize the storage and access of hash keys and other
strings.  This indicates someone tried to decrement the reference count
of a string that can no longer be found in the table.

=item Attempt to free temp prematurely

(W debugging) Mortalized values are supposed to be freed by the
free_tmps() routine.  This indicates that something else is freeing the
SV before the free_tmps() routine gets a chance, which means that the
free_tmps() routine will be freeing an unreferenced scalar when it does
try to free it.

=item Attempt to free unreferenced glob pointers

(P internal) The reference counts got screwed up on symbol aliases.

=item Attempt to free unreferenced scalar

(W internal) Perl went to decrement the reference count of a scalar to
see if it would go to 0, and discovered that it had already gone to 0
earlier, and should have been freed, and in fact, probably was freed.
This could indicate that SvREFCNT_dec() was called too many times, or
that SvREFCNT_inc() was called too few times, or that the SV was
mortalized when it shouldn't have been, or that memory has been
corrupted.

=item Attempt to join self

(F) You tried to join a thread from within itself, which is an
impossible task.  You may be joining the wrong thread, or you may need
to move the join() to some other thread.

=item Attempt to pack pointer to temporary value

(W pack) You tried to pass a temporary value (like the result of a
function, or a computed expression) to the "p" pack() template.  This
means the result contains a pointer to a location that could become
invalid anytime, even before the end of the current statement.  Use
literals or global values as arguments to the "p" pack() template to
avoid this warning.

=item Attempt to use reference as lvalue in substr

(W substr) You supplied a reference as the first argument to substr()
used as an lvalue, which is pretty strange.  Perhaps you forgot to
dereference it first.  See L<perlfunc/substr>.

=item Bad arg length for %s, is %d, should be %s

(F) You passed a buffer of the wrong size to one of msgctl(), semctl()
or shmctl().  In C parlance, the correct sizes are, respectively,
S<sizeof(struct msqid_ds *)>, S<sizeof(struct semid_ds *)>, and
S<sizeof(struct shmid_ds *)>.

=item Bad evalled substitution pattern

(F) You've used the C</e> switch to evaluate the replacement for a
substitution, but perl found a syntax error in the code to evaluate,
most likely an unexpected right brace '}'.

=item Bad filehandle: %s

(F) A symbol was passed to something wanting a filehandle, but the
symbol has no filehandle associated with it.  Perhaps you didn't do an
open(), or did it in another package.

=item Bad free() ignored

(S malloc) An internal routine called free() on something that had never
been malloc()ed in the first place. Mandatory, but can be disabled by
setting environment variable C<PERL_BADFREE> to 0.

This message can be seen quite often with DB_File on systems with "hard"
dynamic linking, like C<AIX> and C<OS/2>. It is a bug of C<Berkeley DB>
which is left unnoticed if C<DB> uses I<forgiving> system malloc().

=item Bad hash

(P) One of the internal hash routines was passed a null HV pointer.

=item Badly placed ()'s

(A) You've accidentally run your script through B<csh> instead
of Perl.  Check the #! line, or manually feed your script into
Perl yourself.

=item Bad name after %s::

(F) You started to name a symbol by using a package prefix, and then
didn't finish the symbol.  In particular, you can't interpolate outside
of quotes, so

    $var = 'myvar';
    $sym = mypack::$var;

is not the same as

    $var = 'myvar';
    $sym = "mypack::$var";

=item Bad realloc() ignored

(S malloc) An internal routine called realloc() on something that had
never been malloc()ed in the first place. Mandatory, but can be disabled
by setting environment variable C<PERL_BADFREE> to 1.

=item Bad symbol for array

(P) An internal request asked to add an array entry to something that
wasn't a symbol table entry.

=item Bad symbol for filehandle

(P) An internal request asked to add a filehandle entry to something
that wasn't a symbol table entry.

=item Bad symbol for hash

(P) An internal request asked to add a hash entry to something that
wasn't a symbol table entry.

=item Bareword found in conditional

(W bareword) The compiler found a bareword where it expected a
conditional, which often indicates that an || or && was parsed as part
of the last argument of the previous construct, for example:

    open FOO || die;

It may also indicate a misspelled constant that has been interpreted as
a bareword:

    use constant TYPO => 1;
    if (TYOP) { print "foo" }

The C<strict> pragma is useful in avoiding such errors.

=item Bareword "%s" not allowed while "strict subs" in use

(F) With "strict subs" in use, a bareword is only allowed as a
subroutine identifier, in curly brackets or to the left of the "=>"
symbol.  Perhaps you need to predeclare a subroutine?

=item Bareword "%s" refers to nonexistent package

(W bareword) You used a qualified bareword of the form C<Foo::>, but the
compiler saw no other uses of that namespace before that point.  Perhaps
you need to predeclare a package?

=item BEGIN failed--compilation aborted

(F) An untrapped exception was raised while executing a BEGIN
subroutine.  Compilation stops immediately and the interpreter is
exited.

=item BEGIN not safe after errors--compilation aborted

(F) Perl found a C<BEGIN {}> subroutine (or a C<use> directive, which
implies a C<BEGIN {}>) after one or more compilation errors had already
occurred.  Since the intended environment for the C<BEGIN {}> could not
be guaranteed (due to the errors), and since subsequent code likely
depends on its correct operation, Perl just gave up.

=item \1 better written as $1

(W syntax) Outside of patterns, backreferences live on as variables.
The use of backslashes is grandfathered on the right-hand side of a
substitution, but stylistically it's better to use the variable form
because other Perl programmers will expect it, and it works better if
there are more than 9 backreferences.

=item Binary number > 0b11111111111111111111111111111111 non-portable

(W portable) The binary number you specified is larger than 2**32-1
(4294967295) and therefore non-portable between systems.  See
L<perlport> for more on portability concerns.

=item bind() on closed socket %s

(W closed) You tried to do a bind on a closed socket.  Did you forget to
check the return value of your socket() call?  See L<perlfunc/bind>.

=item binmode() on closed filehandle %s

(W unopened) You tried binmode() on a filehandle that was never opened.
Check you control flow and number of arguments.

=item Bit vector size > 32 non-portable

(W portable) Using bit vector sizes larger than 32 is non-portable.

=item Bizarre copy of %s in %s

(P) Perl detected an attempt to copy an internal value that is not
copyable.

=item B<-P> not allowed for setuid/setgid script

(F) The script would have to be opened by the C preprocessor by name,
which provides a race condition that breaks security.

=item Buffer overflow in prime_env_iter: %s

(W internal) A warning peculiar to VMS.  While Perl was preparing to
iterate over %ENV, it encountered a logical name or symbol definition
which was too long, so it was truncated to the string shown.

=item Callback called exit

(F) A subroutine invoked from an external package via call_sv()
exited by calling exit.

=item %s() called too early to check prototype

(W prototype) You've called a function that has a prototype before the
parser saw a definition or declaration for it, and Perl could not check
that the call conforms to the prototype.  You need to either add an
early prototype declaration for the subroutine in question, or move the
subroutine definition ahead of the call to get proper prototype
checking.  Alternatively, if you are certain that you're calling the
function correctly, you may put an ampersand before the name to avoid
the warning.  See L<perlsub>.

=item Can only compress unsigned integers

(F) An argument to pack("w",...) was not an integer.  The BER compressed
integer format can only be used with positive integers, and you attempted
to compress something else.  See L<perlfunc/pack>.

=item Cannot compress integer

(F) An argument to pack("w",...) was too large to compress.  The BER
compressed integer format can only be used with positive integers, and you
attempted to compress Infinity or a very large number (> 1e308).
See L<perlfunc/pack>.

=item Cannot compress negative numbers

(F) An argument to pack("w",...) was negative.  The BER compressed integer
format can only be used with positive integers.  See L<perlfunc/pack>.

=item / cannot take a count

(F) You had an unpack template indicating a counted-length string, but
you have also specified an explicit size for the string.  See
L<perlfunc/pack>.

=item Can't bless non-reference value

(F) Only hard references may be blessed.  This is how Perl "enforces"
encapsulation of objects.  See L<perlobj>.

=item Can't call method "%s" in empty package "%s"

(F) You called a method correctly, and it correctly indicated a package
functioning as a class, but that package doesn't have ANYTHING defined
in it, let alone methods.  See L<perlobj>.

=item Can't call method "%s" on an undefined value

(F) You used the syntax of a method call, but the slot filled by the
object reference or package name contains an undefined value.  Something
like this will reproduce the error:

    $BADREF = undef;
    process $BADREF 1,2,3;
    $BADREF->process(1,2,3);

=item Can't call method "%s" on unblessed reference

(F) A method call must know in what package it's supposed to run.  It
ordinarily finds this out from the object reference you supply, but you
didn't supply an object reference in this case.  A reference isn't an
object reference until it has been blessed.  See L<perlobj>.

=item Can't call method "%s" without a package or object reference

(F) You used the syntax of a method call, but the slot filled by the
object reference or package name contains an expression that returns a
defined value which is neither an object reference nor a package name.
Something like this will reproduce the error:

    $BADREF = 42;
    process $BADREF 1,2,3;
    $BADREF->process(1,2,3);

=item Can't chdir to %s

(F) You called C<perl -x/foo/bar>, but C</foo/bar> is not a directory
that you can chdir to, possibly because it doesn't exist.

=item Can't check filesystem of script "%s" for nosuid

(P) For some reason you can't check the filesystem of the script for
nosuid.

=item Can't coerce array into hash

(F) You used an array where a hash was expected, but the array has no
information on how to map from keys to array indices.  You can do that
only with arrays that have a hash reference at index 0.

=item Can't coerce %s to integer in %s

(F) Certain types of SVs, in particular real symbol table entries
(typeglobs), can't be forced to stop being what they are.  So you can't
say things like:

    *foo += 1;

You CAN say

    $foo = *foo;
    $foo += 1;

but then $foo no longer contains a glob.

=item Can't coerce %s to number in %s

(F) Certain types of SVs, in particular real symbol table entries
(typeglobs), can't be forced to stop being what they are.

=item Can't coerce %s to string in %s

(F) Certain types of SVs, in particular real symbol table entries
(typeglobs), can't be forced to stop being what they are.

=item Can't create pipe mailbox

(P) An error peculiar to VMS.  The process is suffering from exhausted
quotas or other plumbing problems.

=item Can't declare class for non-scalar %s in "%s"

(F) Currently, only scalar variables can be declared with a specific
class qualifier in a "my" or "our" declaration.  The semantics may be
extended for other types of variables in future.

=item Can't declare %s in "%s"

(F) Only scalar, array, and hash variables may be declared as "my" or
"our" variables.  They must have ordinary identifiers as names.

=item Can't do inplace edit: %s is not a regular file

(S inplace) You tried to use the B<-i> switch on a special file, such as
a file in /dev, or a FIFO.  The file was ignored.

=item Can't do inplace edit on %s: %s

(S inplace) The creation of the new file failed for the indicated
reason.

=item Can't do inplace edit without backup

(F) You're on a system such as MS-DOS that gets confused if you try
reading from a deleted (but still opened) file.  You have to say
C<-i.bak>, or some such.

=item Can't do inplace edit: %s would not be unique

(S inplace) Your filesystem does not support filenames longer than 14
characters and Perl was unable to create a unique filename during
inplace editing with the B<-i> switch.  The file was ignored.

=item Can't do {n,m} with n > m in regex; marked by <-- HERE in m/%s/

(F) Minima must be less than or equal to maxima. If you really want your
regexp to match something 0 times, just put {0}. The <-- HERE shows in the
regular expression about where the problem was discovered. See L<perlre>.

=item Can't do setegid!

(P) The setegid() call failed for some reason in the setuid emulator of
suidperl.

=item Can't do seteuid!

(P) The setuid emulator of suidperl failed for some reason.

=item Can't do setuid

(F) This typically means that ordinary perl tried to exec suidperl to do
setuid emulation, but couldn't exec it.  It looks for a name of the form
sperl5.000 in the same directory that the perl executable resides under
the name perl5.000, typically /usr/local/bin on Unix machines.  If the
file is there, check the execute permissions.  If it isn't, ask your
sysadmin why he and/or she removed it.

=item Can't do waitpid with flags

(F) This machine doesn't have either waitpid() or wait4(), so only
waitpid() without flags is emulated.

=item Can't emulate -%s on #! line

(F) The #! line specifies a switch that doesn't make sense at this
point.  For example, it'd be kind of silly to put a B<-x> on the #!
line.

=item Can't exec "%s": %s

(W exec) A system(), exec(), or piped open call could not execute the
named program for the indicated reason.  Typical reasons include: the
permissions were wrong on the file, the file wasn't found in
C<$ENV{PATH}>, the executable in question was compiled for another
architecture, or the #! line in a script points to an interpreter that
can't be run for similar reasons.  (Or maybe your system doesn't support
#! at all.)

=item Can't exec %s

(F) Perl was trying to execute the indicated program for you because
that's what the #! line said.  If that's not what you wanted, you may
need to mention "perl" on the #! line somewhere.

=item Can't execute %s

(F) You used the B<-S> switch, but the copies of the script to execute
found in the PATH did not have correct permissions.

=item Can't find an opnumber for "%s"

(F) A string of a form C<CORE::word> was given to prototype(), but there
is no builtin with the name C<word>.

=item Can't find %s character property "%s"

(F) You used C<\p{}> or C<\P{}> but the character property by that name
could not be found. Maybe you misspelled the name of the property
(remember that the names of character properties consist only of
alphanumeric characters), or maybe you forgot the C<Is> or C<In> prefix?

=item Can't find label %s

(F) You said to goto a label that isn't mentioned anywhere that it's
possible for us to go to.  See L<perlfunc/goto>.

=item Can't find %s on PATH

(F) You used the B<-S> switch, but the script to execute could not be
found in the PATH.

=item Can't find %s on PATH, '.' not in PATH

(F) You used the B<-S> switch, but the script to execute could not be
found in the PATH, or at least not with the correct permissions.  The
script exists in the current directory, but PATH prohibits running it.

=item Can't find string terminator %s anywhere before EOF

(F) Perl strings can stretch over multiple lines.  This message means
that the closing delimiter was omitted.  Because bracketed quotes count
nesting levels, the following is missing its final parenthesis:

    print q(The character '(' starts a side comment.);

If you're getting this error from a here-document, you may have included
unseen whitespace before or after your closing tag. A good programmer's
editor will have a way to help you find these characters.

=item Can't find %s property definition %s

(F) You may have tried to use C<\p> which means a Unicode property (for
example C<\p{Lu}> is all uppercase letters).  If you did mean to use a
Unicode property, see L<perlunicode> for the list of known properties.
If you didn't mean to use a Unicode property, escape the C<\p>, either
by C<\\p> (just the C<\p>) or by C<\Q\p> (the rest of the string, until
possible C<\E>).

=item Can't fork

(F) A fatal error occurred while trying to fork while opening a
pipeline.

=item Can't get filespec - stale stat buffer?

(S) A warning peculiar to VMS.  This arises because of the difference
between access checks under VMS and under the Unix model Perl assumes.
Under VMS, access checks are done by filename, rather than by bits in
the stat buffer, so that ACLs and other protections can be taken into
account.  Unfortunately, Perl assumes that the stat buffer contains all
the necessary information, and passes it, instead of the filespec, to
the access checking routine.  It will try to retrieve the filespec using
the device name and FID present in the stat buffer, but this works only
if you haven't made a subsequent call to the CRTL stat() routine,
because the device name is overwritten with each call.  If this warning
appears, the name lookup failed, and the access checking routine gave up
and returned FALSE, just to be conservative.  (Note: The access checking
routine knows about the Perl C<stat> operator and file tests, so you
shouldn't ever see this warning in response to a Perl command; it arises
only if some internal code takes stat buffers lightly.)

=item Can't get pipe mailbox device name

(P) An error peculiar to VMS.  After creating a mailbox to act as a
pipe, Perl can't retrieve its name for later use.

=item Can't get SYSGEN parameter value for MAXBUF

(P) An error peculiar to VMS.  Perl asked $GETSYI how big you want your
mailbox buffers to be, and didn't get an answer.

=item Can't "goto" into the middle of a foreach loop

(F) A "goto" statement was executed to jump into the middle of a foreach
loop.  You can't get there from here.  See L<perlfunc/goto>.

=item Can't "goto" out of a pseudo block

(F) A "goto" statement was executed to jump out of what might look like
a block, except that it isn't a proper block.  This usually occurs if
you tried to jump out of a sort() block or subroutine, which is a no-no.
See L<perlfunc/goto>.

=item Can't goto subroutine from an eval-string

(F) The "goto subroutine" call can't be used to jump out of an eval
"string".  (You can use it to jump out of an eval {BLOCK}, but you
probably don't want to.)

=item Can't goto subroutine outside a subroutine

(F) The deeply magical "goto subroutine" call can only replace one
subroutine call for another.  It can't manufacture one out of whole
cloth.  In general you should be calling it out of only an AUTOLOAD
routine anyway.  See L<perlfunc/goto>.

=item Can't ignore signal CHLD, forcing to default

(W signal) Perl has detected that it is being run with the SIGCHLD
signal (sometimes known as SIGCLD) disabled.  Since disabling this
signal will interfere with proper determination of exit status of child
processes, Perl has reset the signal to its default value.  This
situation typically indicates that the parent program under which Perl
may be running (e.g. cron) is being very careless.

=item Can't "last" outside a loop block

(F) A "last" statement was executed to break out of the current block,
except that there's this itty bitty problem called there isn't a current
block.  Note that an "if" or "else" block doesn't count as a "loopish"
block, as doesn't a block given to sort(), map() or grep().  You can
usually double the curlies to get the same effect though, because the
inner curlies will be considered a block that loops once.  See
L<perlfunc/last>.

=item Can't localize lexical variable %s

(F) You used local on a variable name that was previously declared as a
lexical variable using "my".  This is not allowed.  If you want to
localize a package variable of the same name, qualify it with the
package name.

=item Can't localize through a reference

(F) You said something like C<local $$ref>, which Perl can't currently
handle, because when it goes to restore the old value of whatever $ref
pointed to after the scope of the local() is finished, it can't be sure
that $ref will still be a reference.

=item Can't locate %s

(F) You said to C<do> (or C<require>, or C<use>) a file that couldn't be
found. Perl looks for the file in all the locations mentioned in @INC,
unless the file name included the full path to the file.  Perhaps you
need to set the PERL5LIB or PERL5OPT environment variable to say where
the extra library is, or maybe the script needs to add the library name
to @INC.  Or maybe you just misspelled the name of the file.  See
L<perlfunc/require> and L<lib>.

=item Can't locate auto/%s.al in @INC

(F) A function (or method) was called in a package which allows
autoload, but there is no function to autoload.  Most probable causes
are a misprint in a function/method name or a failure to C<AutoSplit>
the file, say, by doing C<make install>.

=item Can't locate object method "%s" via package "%s"

(F) You called a method correctly, and it correctly indicated a package
functioning as a class, but that package doesn't define that particular
method, nor does any of its base classes.  See L<perlobj>.

=item Can't locate PerlIO%s

(F) You tried to use in open() a PerlIO layer that does not exist,
e.g. open(FH, ">:nosuchlayer", "somefile").

=item (perhaps you forgot to load "%s"?)

(F) This is an educated guess made in conjunction with the message
"Can't locate object method \"%s\" via package \"%s\"".  It often means
that a method requires a package that has not been loaded.

=item Can't locate package %s for @%s::ISA

(W syntax) The @ISA array contained the name of another package that
doesn't seem to exist.

=item Can't make list assignment to \%ENV on this system

(F) List assignment to %ENV is not supported on some systems, notably
VMS.

=item Can't modify %s in %s

(F) You aren't allowed to assign to the item indicated, or otherwise try
to change it, such as with an auto-increment.

=item Can't modify nonexistent substring

(P) The internal routine that does assignment to a substr() was handed
a NULL.

=item Can't modify non-lvalue subroutine call

(F) Subroutines meant to be used in lvalue context should be declared as
such, see L<perlsub/"Lvalue subroutines">.

=item Can't msgrcv to read-only var

(F) The target of a msgrcv must be modifiable to be used as a receive
buffer.

=item Can't "next" outside a loop block

(F) A "next" statement was executed to reiterate the current block, but
there isn't a current block.  Note that an "if" or "else" block doesn't
count as a "loopish" block, as doesn't a block given to sort(), map() or
grep().  You can usually double the curlies to get the same effect
though, because the inner curlies will be considered a block that loops
once.  See L<perlfunc/next>.

=item Can't open %s: %s

(S inplace) The implicit opening of a file through use of the C<< <> >>
filehandle, either implicitly under the C<-n> or C<-p> command-line
switches, or explicitly, failed for the indicated reason.  Usually this
is because you don't have read permission for a file which you named on
the command line.

=item Can't open a reference

(W io) You tried to open a scalar reference for reading or writing,
using the 3-arg open() syntax :

    open FH, '>', $ref;

but your version of perl is compiled without perlio, and this form of
open is not supported.

=item Can't open bidirectional pipe

(W pipe) You tried to say C<open(CMD, "|cmd|")>, which is not supported.
You can try any of several modules in the Perl library to do this, such
as IPC::Open2.  Alternately, direct the pipe's output to a file using
">", and then read it in under a different file handle.

=item Can't open error file %s as stderr

(F) An error peculiar to VMS.  Perl does its own command line
redirection, and couldn't open the file specified after '2>' or '2>>' on
the command line for writing.

=item Can't open input file %s as stdin

(F) An error peculiar to VMS.  Perl does its own command line
redirection, and couldn't open the file specified after '<' on the
command line for reading.

=item Can't open output file %s as stdout

(F) An error peculiar to VMS.  Perl does its own command line
redirection, and couldn't open the file specified after '>' or '>>' on
the command line for writing.

=item Can't open output pipe (name: %s)

(P) An error peculiar to VMS.  Perl does its own command line
redirection, and couldn't open the pipe into which to send data destined
for stdout.

=item Can't open perl script%s: %s

(F) The script you specified can't be opened for the indicated reason.

=item Can't read CRTL environ

(S) A warning peculiar to VMS.  Perl tried to read an element of %ENV
from the CRTL's internal environment array and discovered the array was
missing.  You need to figure out where your CRTL misplaced its environ
or define F<PERL_ENV_TABLES> (see L<perlvms>) so that environ is not
searched.

=item Can't redefine active sort subroutine %s

(F) Perl optimizes the internal handling of sort subroutines and keeps
pointers into them.  You tried to redefine one such sort subroutine when
it was currently active, which is not allowed.  If you really want to do
this, you should write C<sort { &func } @x> instead of C<sort func @x>.

=item Can't "redo" outside a loop block

(F) A "redo" statement was executed to restart the current block, but
there isn't a current block.  Note that an "if" or "else" block doesn't
count as a "loopish" block, as doesn't a block given to sort(), map()
or grep().  You can usually double the curlies to get the same effect
though, because the inner curlies will be considered a block that
loops once.  See L<perlfunc/redo>.

=item Can't remove %s: %s, skipping file

(S inplace) You requested an inplace edit without creating a backup
file.  Perl was unable to remove the original file to replace it with
the modified file.  The file was left unmodified.

=item Can't rename %s to %s: %s, skipping file

(S inplace) The rename done by the B<-i> switch failed for some reason,
probably because you don't have write permission to the directory.

=item Can't reopen input pipe (name: %s) in binary mode

(P) An error peculiar to VMS.  Perl thought stdin was a pipe, and tried
to reopen it to accept binary data.  Alas, it failed.

=item Can't resolve method `%s' overloading `%s' in package `%s'

(F|P) Error resolving overloading specified by a method name (as opposed
to a subroutine reference): no such method callable via the package. If
method name is C<???>, this is an internal error.

=item Can't reswap uid and euid

(P) The setreuid() call failed for some reason in the setuid emulator of
suidperl.

=item Can't return %s from lvalue subroutine

(F) Perl detected an attempt to return illegal lvalues (such as
temporary or readonly values) from a subroutine used as an lvalue.  This
is not allowed.

=item Can't return %s to lvalue scalar context

(F) You tried to return a complete array or hash from an lvalue subroutine,
but you called the subroutine in a way that made Perl think you meant
to return only one value. You probably meant to write parentheses around
the call to the subroutine, which tell Perl that the call should be in
list context.

=item Can't return outside a subroutine

(F) The return statement was executed in mainline code, that is, where
there was no subroutine call to return out of.  See L<perlsub>.

=item Can't stat script "%s"

(P) For some reason you can't fstat() the script even though you have it
open already.  Bizarre.

=item Can't swap uid and euid

(P) The setreuid() call failed for some reason in the setuid emulator of
suidperl.

=item Can't take log of %g

(F) For ordinary real numbers, you can't take the logarithm of a
negative number or zero. There's a Math::Complex package that comes
standard with Perl, though, if you really want to do that for the
negative numbers.

=item Can't take sqrt of %g

(F) For ordinary real numbers, you can't take the square root of a
negative number.  There's a Math::Complex package that comes standard
with Perl, though, if you really want to do that.

=item Can't undef active subroutine

(F) You can't undefine a routine that's currently running.  You can,
however, redefine it while it's running, and you can even undef the
redefined subroutine while the old routine is running.  Go figure.

=item Can't unshift

(F) You tried to unshift an "unreal" array that can't be unshifted, such
as the main Perl stack.

=item Can't upgrade that kind of scalar

(P) The internal sv_upgrade routine adds "members" to an SV, making it
into a more specialized kind of SV.  The top several SV types are so
specialized, however, that they cannot be interconverted.  This message
indicates that such a conversion was attempted.

=item Can't upgrade to undef

(P) The undefined SV is the bottom of the totem pole, in the scheme of
upgradability.  Upgrading to undef indicates an error in the code
calling sv_upgrade.

=item Can't use an undefined value as %s reference

(F) A value used as either a hard reference or a symbolic reference must
be a defined value.  This helps to delurk some insidious errors.

=item Can't use anonymous symbol table for method lookup

(P) The internal routine that does method lookup was handed a symbol
table that doesn't have a name.  Symbol tables can become anonymous
for example by undefining stashes: C<undef %Some::Package::>.

=item Can't use bareword ("%s") as %s ref while "strict refs" in use

(F) Only hard references are allowed by "strict refs".  Symbolic
references are disallowed.  See L<perlref>.

=item Can't use %! because Errno.pm is not available

(F) The first time the %! hash is used, perl automatically loads the
Errno.pm module. The Errno module is expected to tie the %! hash to
provide symbolic names for C<$!> errno values.

=item Can't use %s for loop variable

(F) Only a simple scalar variable may be used as a loop variable on a
foreach.

=item Can't use global %s in "my"

(F) You tried to declare a magical variable as a lexical variable.  This
is not allowed, because the magic can be tied to only one location
(namely the global variable) and it would be incredibly confusing to
have variables in your program that looked like magical variables but
weren't.

=item Can't use "my %s" in sort comparison

(F) The global variables $a and $b are reserved for sort comparisons.
You mentioned $a or $b in the same line as the <=> or cmp operator,
and the variable had earlier been declared as a lexical variable.
Either qualify the sort variable with the package name, or rename the
lexical variable.

=item Can't use %s ref as %s ref

(F) You've mixed up your reference types.  You have to dereference a
reference of the type needed.  You can use the ref() function to
test the type of the reference, if need be.

=item Can't use string ("%s") as %s ref while "strict refs" in use

(F) Only hard references are allowed by "strict refs".  Symbolic
references are disallowed.  See L<perlref>.

=item Can't use subscript on %s

(F) The compiler tried to interpret a bracketed expression as a
subscript.  But to the left of the brackets was an expression that
didn't look like an array reference, or anything else subscriptable.

=item Can't use \%c to mean $%c in expression

(W syntax) In an ordinary expression, backslash is a unary operator that
creates a reference to its argument.  The use of backslash to indicate a
backreference to a matched substring is valid only as part of a regular
expression pattern.  Trying to do this in ordinary Perl code produces a
value that prints out looking like SCALAR(0xdecaf).  Use the $1 form
instead.

=item Can't weaken a nonreference

(F) You attempted to weaken something that was not a reference.  Only
references can be weakened.

=item Can't x= to read-only value

(F) You tried to repeat a constant value (often the undefined value)
with an assignment operator, which implies modifying the value itself.
Perhaps you need to copy the value to a temporary, and repeat that.

=item Character in "C" format wrapped

(W pack) You said

    pack("C", $x)

where $x is either less than 0 or more than 255; the C<"C"> format is
only for encoding native operating system characters (ASCII, EBCDIC,
and so on) and not for Unicode characters, so Perl behaved as if you meant

    pack("C", $x & 255)

If you actually want to pack Unicode codepoints, use the C<"U"> format
instead.

=item Character in "c" format wrapped

(W pack) You said

    pack("c", $x)

where $x is either less than -128 or more than 127; the C<"c"> format
is only for encoding native operating system characters (ASCII, EBCDIC,
and so on) and not for Unicode characters, so Perl behaved as if you meant

    pack("c", $x & 255);

If you actually want to pack Unicode codepoints, use the C<"U"> format
instead.

=item close() on unopened filehandle %s

(W unopened) You tried to close a filehandle that was never opened.

=item %s: Command not found

(A) You've accidentally run your script through B<csh> instead of Perl.
Check the #! line, or manually feed your script into Perl yourself.

=item Compilation failed in require

(F) Perl could not compile a file specified in a C<require> statement.
Perl uses this generic message when none of the errors that it
encountered were severe enough to halt compilation immediately.

=item Complex regular subexpression recursion limit (%d) exceeded

(W regexp) The regular expression engine uses recursion in complex
situations where back-tracking is required.  Recursion depth is limited
to 32766, or perhaps less in architectures where the stack cannot grow
arbitrarily.  ("Simple" and "medium" situations are handled without
recursion and are not subject to a limit.)  Try shortening the string
under examination; looping in Perl code (e.g. with C<while>) rather than
in the regular expression engine; or rewriting the regular expression so
that it is simpler or backtracks less.  (See L<perlfaq2> for information
on I<Mastering Regular Expressions>.)

=item cond_broadcast() called on unlocked variable

(W threads) Within a thread-enabled program, you tried to call
cond_broadcast() on a variable which wasn't locked. The cond_broadcast()
function  is used to wake up another thread that is waiting in a
cond_wait(). To ensure that the signal isn't sent before the other thread
has a chance to enter the wait, it is usual for the signaling thread to
first wait for a lock on variable. This lock attempt will only succeed
after the other thread has entered cond_wait() and thus relinquished the
lock.


=item cond_signal() called on unlocked variable

(W threads) Within a thread-enabled program, you tried to call
cond_signal() on a variable which wasn't locked. The cond_signal()
function  is used to wake up another thread that is waiting in a
cond_wait(). To ensure that the signal isn't sent before the other thread
has a chance to enter the wait, it is usual for the signaling thread to
first wait for a lock on variable. This lock attempt will only succeed
after the other thread has entered cond_wait() and thus relinquished the
lock.

=item connect() on closed socket %s

(W closed) You tried to do a connect on a closed socket.  Did you forget
to check the return value of your socket() call?  See
L<perlfunc/connect>.

=item Constant(%s)%s: %s

(F) The parser found inconsistencies either while attempting to define
an overloaded constant, or when trying to find the character name
specified in the C<\N{...}> escape.  Perhaps you forgot to load the
corresponding C<overload> or C<charnames> pragma?  See L<charnames> and
L<overload>.

=item Constant is not %s reference

(F) A constant value (perhaps declared using the C<use constant> pragma)
is being dereferenced, but it amounts to the wrong type of reference.
The message indicates the type of reference that was expected. This
usually indicates a syntax error in dereferencing the constant value.
See L<perlsub/"Constant Functions"> and L<constant>.

=item Constant subroutine %s redefined

(S) You redefined a subroutine which had previously been
eligible for inlining.  See L<perlsub/"Constant Functions"> for
commentary and workarounds.

=item Constant subroutine %s undefined

(W misc) You undefined a subroutine which had previously been eligible
for inlining.  See L<perlsub/"Constant Functions"> for commentary and
workarounds.

=item Copy method did not return a reference

(F) The method which overloads "=" is buggy. See
L<overload/Copy Constructor>.

=item CORE::%s is not a keyword

(F) The CORE:: namespace is reserved for Perl keywords.

=item corrupted regexp pointers

(P) The regular expression engine got confused by what the regular
expression compiler gave it.

=item corrupted regexp program

(P) The regular expression engine got passed a regexp program without a
valid magic number.

=item Corrupt malloc ptr 0x%lx at 0x%lx

(P) The malloc package that comes with Perl had an internal failure.

=item C<-p> destination: %s

(F) An error occurred during the implicit output invoked by the C<-p>
command-line switch.  (This output goes to STDOUT unless you've
redirected it with select().)

=item C<-T> and C<-B> not implemented on filehandles

(F) Perl can't peek at the stdio buffer of filehandles when it doesn't
know about your kind of stdio.  You'll have to use a filename instead.

=item Deep recursion on subroutine "%s"

(W recursion) This subroutine has called itself (directly or indirectly)
100 times more than it has returned.  This probably indicates an
infinite recursion, unless you're writing strange benchmark programs, in
which case it indicates something else.

=item defined(@array) is deprecated

(D deprecated) defined() is not usually useful on arrays because it
checks for an undefined I<scalar> value.  If you want to see if the
array is empty, just use C<if (@array) { # not empty }> for example.

=item defined(%hash) is deprecated

(D deprecated) defined() is not usually useful on hashes because it
checks for an undefined I<scalar> value.  If you want to see if the hash
is empty, just use C<if (%hash) { # not empty }> for example.

=item %s defines neither package nor VERSION--version check failed

(F) You said something like "use Module 42" but in the Module file
there are neither package declarations nor a C<$VERSION>.

=item Delimiter for here document is too long

(F) In a here document construct like C<<<FOO>, the label C<FOO> is too
long for Perl to handle.  You have to be seriously twisted to write code
that triggers this error.

=item Did not produce a valid header

See Server error.

=item %s did not return a true value

(F) A required (or used) file must return a true value to indicate that
it compiled correctly and ran its initialization code correctly.  It's
traditional to end such a file with a "1;", though any true value would
do.  See L<perlfunc/require>.

=item (Did you mean &%s instead?)

(W) You probably referred to an imported subroutine &FOO as $FOO or some
such.

=item (Did you mean "local" instead of "our"?)

(W misc) Remember that "our" does not localize the declared global
variable.  You have declared it again in the same lexical scope, which
seems superfluous.

=item (Did you mean $ or @ instead of %?)

(W) You probably said %hash{$key} when you meant $hash{$key} or
@hash{@keys}.  On the other hand, maybe you just meant %hash and got
carried away.

=item Died

(F) You passed die() an empty string (the equivalent of C<die "">) or
you called it with no args and both C<$@> and C<$_> were empty.

=item Document contains no data

See Server error.

=item %s does not define %s::VERSION--version check failed

(F) You said something like "use Module 42" but the Module did not
define a C<$VERSION.>

=item Don't know how to handle magic of type '%s'

(P) The internal handling of magical variables has been cursed.

=item do_study: out of memory

(P) This should have been caught by safemalloc() instead.

=item (Do you need to predeclare %s?)

(S) This is an educated guess made in conjunction with the message "%s
found where operator expected".  It often means a subroutine or module
name is being referenced that hasn't been declared yet.  This may be
because of ordering problems in your file, or because of a missing
"sub", "package", "require", or "use" statement.  If you're referencing
something that isn't defined yet, you don't actually have to define the
subroutine or package before the current location.  You can use an empty
"sub foo;" or "package FOO;" to enter a "forward" declaration.

=item dump() better written as CORE::dump()

(W misc) You used the obsolescent C<dump()> built-in function, without fully
qualifying it as C<CORE::dump()>.  Maybe it's a typo.  See L<perlfunc/dump>.

=item Duplicate free() ignored

(S malloc) An internal routine called free() on something that had
already been freed.

=item elseif should be elsif

(S) There is no keyword "elseif" in Perl because Larry thinks it's ugly.
Your code will be interpreted as an attempt to call a method named
"elseif" for the class returned by the following block.  This is
unlikely to be what you want.

=item Empty %s

(F) C<\p> and C<\P> are used to introduce a named Unicode property, as
described in L<perlunicode> and L<perlre>. You used C<\p> or C<\P> in
a regular expression without specifying the property name.

=item entering effective %s failed

(F) While under the C<use filetest> pragma, switching the real and
effective uids or gids failed.

=item Error converting file specification %s

(F) An error peculiar to VMS.  Because Perl may have to deal with file
specifications in either VMS or Unix syntax, it converts them to a
single form when it must operate on them directly.  Either you've passed
an invalid file specification to Perl, or you've found a case the
conversion routines don't handle.  Drat.

=item %s: Eval-group in insecure regular expression

(F) Perl detected tainted data when trying to compile a regular
expression that contains the C<(?{ ... })> zero-width assertion, which
is unsafe.  See L<perlre/(?{ code })>, and L<perlsec>.

=item %s: Eval-group not allowed at run time

(F) Perl tried to compile a regular expression containing the
C<(?{ ... })> zero-width assertion at run time, as it would when the
pattern contains interpolated values.  Since that is a security risk, it
is not allowed.  If you insist, you may still do this by explicitly
building the pattern from an interpolated string at run time and using
that in an eval().  See L<perlre/(?{ code })>.

=item %s: Eval-group not allowed, use re 'eval'

(F) A regular expression contained the C<(?{ ... })> zero-width
assertion, but that construct is only allowed when the C<use re 'eval'>
pragma is in effect.  See L<perlre/(?{ code })>.

=item Excessively long <> operator

(F) The contents of a <> operator may not exceed the maximum size of a
Perl identifier.  If you're just trying to glob a long list of
filenames, try using the glob() operator, or put the filenames into a
variable and glob that.

=item exec? I'm not *that* kind of operating system

(F) The C<exec> function is not implemented in MacPerl. See L<perlport>.

=item Execution of %s aborted due to compilation errors

(F) The final summary message when a Perl compilation fails.

=item Exiting eval via %s

(W exiting) You are exiting an eval by unconventional means, such as a
goto, or a loop control statement.

=item Exiting format via %s

(W exiting) You are exiting a format by unconventional means, such as a
goto, or a loop control statement.

=item Exiting pseudo-block via %s

(W exiting) You are exiting a rather special block construct (like a
sort block or subroutine) by unconventional means, such as a goto, or a
loop control statement.  See L<perlfunc/sort>.

=item Exiting subroutine via %s

(W exiting) You are exiting a subroutine by unconventional means, such
as a goto, or a loop control statement.

=item Exiting substitution via %s

(W exiting) You are exiting a substitution by unconventional means, such
as a return, a goto, or a loop control statement.

=item Explicit blessing to '' (assuming package main)

(W misc) You are blessing a reference to a zero length string.  This has
the effect of blessing the reference into the package main.  This is
usually not what you want.  Consider providing a default target package,
e.g. bless($ref, $p || 'MyPackage');

=item %s: Expression syntax

(A) You've accidentally run your script through B<csh> instead of Perl.
Check the #! line, or manually feed your script into Perl yourself.

=item %s failed--call queue aborted

(F) An untrapped exception was raised while executing a CHECK, INIT, or
END subroutine.  Processing of the remainder of the queue of such
routines has been prematurely ended.

=item False [] range "%s" in regex; marked by <-- HERE in m/%s/

(W regexp) A character class range must start and end at a literal
character, not another character class like C<\d> or C<[:alpha:]>.  The "-"
in your false range is interpreted as a literal "-".  Consider quoting the
"-", "\-".  The <-- HERE shows in the regular expression about where the
problem was discovered.  See L<perlre>.

=item Fatal VMS error at %s, line %d

(P) An error peculiar to VMS.  Something untoward happened in a VMS
system service or RTL routine; Perl's exit status should provide more
details.  The filename in "at %s" and the line number in "line %d" tell
you which section of the Perl source code is distressed.

=item fcntl is not implemented

(F) Your machine apparently doesn't implement fcntl().  What is this, a
PDP-11 or something?

=item Filehandle %s opened only for input

(W io) You tried to write on a read-only filehandle.  If you intended it
to be a read-write filehandle, you needed to open it with "+<" or "+>"
or "+>>" instead of with "<" or nothing.  If you intended only to write
the file, use ">" or ">>".  See L<perlfunc/open>.

=item Filehandle %s opened only for output

(W io) You tried to read from a filehandle opened only for writing.
If you intended it to be a read/write filehandle, you needed to open it
with "+<" or "+>" or "+>>" instead of with "<" or nothing.  If you
intended only to read from the file, use "<".  See L<perlfunc/open>.

=item Filehandle %s reopened as %s only for input

(W io) You opened for reading a filehandle that got the same filehandle id
as STDOUT or STDERR. This occured because you closed STDOUT or STDERR
previously.

=item Filehandle STDIN reopened as %s only for output

(W io) You opened for writing a filehandle that got the same filehandle id
as STDIN. This occured because you closed STDIN previously.

=item Final $ should be \$ or $name

(F) You must now decide whether the final $ in a string was meant to be
a literal dollar sign, or was meant to introduce a variable name that
happens to be missing.  So you have to put either the backslash or the
name.

=item Final @ should be \@ or @name

(F) You must now decide whether the final @ in a string was meant to be
a literal "at" sign, or was meant to introduce a variable name that
happens to be missing.  So you have to put either the backslash or the
name.

=item flock() on closed filehandle %s

(W closed) The filehandle you're attempting to flock() got itself closed
some time before now.  Check your control flow.  flock() operates on
filehandles.  Are you attempting to call flock() on a dirhandle by the
same name?

=item Quantifier follows nothing in regex;

marked by <-- HERE in m/%s/

(F) You started a regular expression with a quantifier. Backslash it if you
meant it literally. The <-- HERE shows in the regular expression about
where the problem was discovered. See L<perlre>.

=item Format not terminated

(F) A format must be terminated by a line with a solitary dot.  Perl got
to the end of your file without finding such a line.

=item Format %s redefined

(W redefine) You redefined a format.  To suppress this warning, say

    {
        no warnings 'redefine';
        eval "format NAME =...";
    }

=item Found = in conditional, should be ==

(W syntax) You said

    if ($foo = 123)

when you meant

    if ($foo == 123)

(or something like that).

=item %s found where operator expected

(S) The Perl lexer knows whether to expect a term or an operator.  If it
sees what it knows to be a term when it was expecting to see an
operator, it gives you this warning.  Usually it indicates that an
operator or delimiter was omitted, such as a semicolon.

=item gdbm store returned %d, errno %d, key "%s"

(S) A warning from the GDBM_File extension that a store failed.

=item gethostent not implemented

(F) Your C library apparently doesn't implement gethostent(), probably
because if it did, it'd feel morally obligated to return every hostname
on the Internet.

=item get%sname() on closed socket %s

(W closed) You tried to get a socket or peer socket name on a closed
socket.  Did you forget to check the return value of your socket() call?

=item getpwnam returned invalid UIC %#o for user "%s"

(S) A warning peculiar to VMS.  The call to C<sys$getuai> underlying the
C<getpwnam> operator returned an invalid UIC.

=item getsockopt() on closed socket %s

(W closed) You tried to get a socket option on a closed socket.  Did you
forget to check the return value of your socket() call?  See
L<perlfunc/getsockopt>.

=item Global symbol "%s" requires explicit package name

(F) You've said "use strict vars", which indicates that all variables
must either be lexically scoped (using "my"), declared beforehand using
"our", or explicitly qualified to say which package the global variable
is in (using "::").

=item glob failed (%s)

(W glob) Something went wrong with the external program(s) used for
C<glob> and C<< <*.c> >>.  Usually, this means that you supplied a
C<glob> pattern that caused the external program to fail and exit with a
nonzero status.  If the message indicates that the abnormal exit
resulted in a coredump, this may also mean that your csh (C shell) is
broken.  If so, you should change all of the csh-related variables in
config.sh:  If you have tcsh, make the variables refer to it as if it
were csh (e.g.  C<full_csh='/usr/bin/tcsh'>); otherwise, make them all
empty (except that C<d_csh> should be C<'undef'>) so that Perl will
think csh is missing.  In either case, after editing config.sh, run
C<./Configure -S> and rebuild Perl.

=item Glob not terminated

(F) The lexer saw a left angle bracket in a place where it was expecting
a term, so it's looking for the corresponding right angle bracket, and
not finding it.  Chances are you left some needed parentheses out
earlier in the line, and you really meant a "less than".

=item Got an error from DosAllocMem

(P) An error peculiar to OS/2.  Most probably you're using an obsolete
version of Perl, and this should not happen anyway.

=item goto must have label

(F) Unlike with "next" or "last", you're not allowed to goto an
unspecified destination.  See L<perlfunc/goto>.

=item %s-group starts with a count

(F) In pack/unpack a ()-group started with a count.  A count is
supposed to follow something: a template character or a ()-group.

=item %s had compilation errors

(F) The final summary message when a C<perl -c> fails.

=item Had to create %s unexpectedly

(S internal) A routine asked for a symbol from a symbol table that ought
to have existed already, but for some reason it didn't, and had to be
created on an emergency basis to prevent a core dump.

=item Hash %%s missing the % in argument %d of %s()

(D deprecated) Really old Perl let you omit the % on hash names in some
spots.  This is now heavily deprecated.

=item %s has too many errors

(F) The parser has given up trying to parse the program after 10 errors.
Further error messages would likely be uninformative.

=item Hexadecimal number > 0xffffffff non-portable

(W portable) The hexadecimal number you specified is larger than 2**32-1
(4294967295) and therefore non-portable between systems.  See
L<perlport> for more on portability concerns.

=item Identifier too long

(F) Perl limits identifiers (names for variables, functions, etc.) to
about 250 characters for simple names, and somewhat more for compound
names (like C<$A::B>).  You've exceeded Perl's limits.  Future versions
of Perl are likely to eliminate these arbitrary limitations.

=item Illegal binary digit %s

(F) You used a digit other than 0 or 1 in a binary number.

=item Illegal binary digit %s ignored

(W digit) You may have tried to use a digit other than 0 or 1 in a
binary number.  Interpretation of the binary number stopped before the
offending digit.

=item Illegal character %s (carriage return)

(F) Perl normally treats carriage returns in the program text as it
would any other whitespace, which means you should never see this error
when Perl was built using standard options.  For some reason, your
version of Perl appears to have been built without this support.  Talk
to your Perl administrator.

=item Illegal character in prototype for %s : %s

(W syntax) An illegal character was found in a prototype declaration.  Legal
characters in prototypes are $, @, %, *, ;, [, ], &, and \.

=item Illegal declaration of anonymous subroutine

(F) When using the C<sub> keyword to construct an anonymous subroutine,
you must always specify a block of code. See L<perlsub>.

=item Illegal division by zero

(F) You tried to divide a number by 0.  Either something was wrong in
your logic, or you need to put a conditional in to guard against
meaningless input.

=item Illegal hexadecimal digit %s ignored

(W digit) You may have tried to use a character other than 0 - 9 or
A - F, a - f in a hexadecimal number.  Interpretation of the hexadecimal
number stopped before the illegal character.

=item Illegal modulus zero

(F) You tried to divide a number by 0 to get the remainder.  Most
numbers don't take to this kindly.

=item Illegal number of bits in vec

(F) The number of bits in vec() (the third argument) must be a power of
two from 1 to 32 (or 64, if your platform supports that).

=item Illegal octal digit %s

(F) You used an 8 or 9 in an octal number.

=item Illegal octal digit %s ignored

(W digit) You may have tried to use an 8 or 9 in an octal number.
Interpretation of the octal number stopped before the 8 or 9.

=item Illegal switch in PERL5OPT: %s

(X) The PERL5OPT environment variable may only be used to set the
following switches: B<-[DIMUdmtw]>.

=item Ill-formed CRTL environ value "%s"

(W internal) A warning peculiar to VMS.  Perl tried to read the CRTL's
internal environ array, and encountered an element without the C<=>
delimiter used to separate keys from values.  The element is ignored.

=item Ill-formed message in prime_env_iter: |%s|

(W internal) A warning peculiar to VMS.  Perl tried to read a logical
name or CLI symbol definition when preparing to iterate over %ENV, and
didn't see the expected delimiter between key and value, so the line was
ignored.

=item (in cleanup) %s

(W misc) This prefix usually indicates that a DESTROY() method raised
the indicated exception.  Since destructors are usually called by the
system at arbitrary points during execution, and often a vast number of
times, the warning is issued only once for any number of failures that
would otherwise result in the same message being repeated.

Failure of user callbacks dispatched using the C<G_KEEPERR> flag could
also result in this warning.  See L<perlcall/G_KEEPERR>.

=item In EBCDIC the v-string components cannot exceed 2147483647

(F) An error peculiar to EBCDIC.  Internally, v-strings are stored as
Unicode code points, and encoded in EBCDIC as UTF-EBCDIC.  The UTF-EBCDIC
encoding is limited to code points no larger than 2147483647 (0x7FFFFFFF).

=item Insecure dependency in %s

(F) You tried to do something that the tainting mechanism didn't like.
The tainting mechanism is turned on when you're running setuid or
setgid, or when you specify B<-T> to turn it on explicitly.  The
tainting mechanism labels all data that's derived directly or indirectly
from the user, who is considered to be unworthy of your trust.  If any
such data is used in a "dangerous" operation, you get this error.  See
L<perlsec> for more information.

=item Insecure directory in %s

(F) You can't use system(), exec(), or a piped open in a setuid or
setgid script if C<$ENV{PATH}> contains a directory that is writable by
the world.  See L<perlsec>.

=item Insecure $ENV{%s} while running %s

(F) You can't use system(), exec(), or a piped open in a setuid or
setgid script if any of C<$ENV{PATH}>, C<$ENV{IFS}>, C<$ENV{CDPATH}>,
C<$ENV{ENV}> or C<$ENV{BASH_ENV}> are derived from data supplied (or
potentially supplied) by the user.  The script must set the path to a
known value, using trustworthy data.  See L<perlsec>.

=item Integer overflow in %s number

(W overflow) The hexadecimal, octal or binary number you have specified
either as a literal or as an argument to hex() or oct() is too big for
your architecture, and has been converted to a floating point number.
On a 32-bit architecture the largest hexadecimal, octal or binary number
representable without overflow is 0xFFFFFFFF, 037777777777, or
0b11111111111111111111111111111111 respectively.  Note that Perl
transparently promotes all numbers to a floating point representation
internally--subject to loss of precision errors in subsequent
operations.

=item Integer overflow in version

(F) Some portion of a version initialization is too large for the
size of integers for your architecture.  This is not a warning
because there is no rational reason for a version to try and use a
element larger than typically 2**32.  This is usually caused by
trying to use some odd mathematical operation as a version, like
100/9.

=item Internal disaster in regex; marked by <-- HERE in m/%s/

(P) Something went badly wrong in the regular expression parser.
The <-- HERE shows in the regular expression about where the problem was
discovered.

=item Internal inconsistency in tracking vforks

(S) A warning peculiar to VMS.  Perl keeps track of the number of times
you've called C<fork> and C<exec>, to determine whether the current call
to C<exec> should affect the current script or a subprocess (see
L<perlvms/"exec LIST">).  Somehow, this count has become scrambled, so
Perl is making a guess and treating this C<exec> as a request to
terminate the Perl script and execute the specified command.

=item Internal urp in regex; marked by <-- HERE in m/%s/

(P) Something went badly awry in the regular expression parser. The
<-- HERE shows in the regular expression about where the problem was
discovered.

=item %s (...) interpreted as function

(W syntax) You've run afoul of the rule that says that any list operator
followed by parentheses turns into a function, with all the list
operators arguments found inside the parentheses.  See
L<perlop/Terms and List Operators (Leftward)>.

=item Invalid %s attribute: %s

The indicated attribute for a subroutine or variable was not recognized
by Perl or by a user-supplied handler.  See L<attributes>.

=item Invalid %s attributes: %s

The indicated attributes for a subroutine or variable were not
recognized by Perl or by a user-supplied handler.  See L<attributes>.

=item Invalid conversion in %s: "%s"

(W printf) Perl does not understand the given format conversion.  See
L<perlfunc/sprintf>.

=item Invalid [] range "%s" in regex; marked by <-- HERE in m/%s/

(F) The range specified in a character class had a minimum character
greater than the maximum character.  One possibility is that you forgot the
C<{}> from your ending C<\x{}> - C<\x> without the curly braces can go only
up to C<ff>.  The <-- HERE shows in the regular expression about where the
problem was discovered.  See L<perlre>.

=item Invalid range "%s" in transliteration operator

(F) The range specified in the tr/// or y/// operator had a minimum
character greater than the maximum character.  See L<perlop>.

=item Invalid separator character %s in attribute list

(F) Something other than a colon or whitespace was seen between the
elements of an attribute list.  If the previous attribute had a
parenthesised parameter list, perhaps that list was terminated too soon.
See L<attributes>.

=item Invalid type in pack: '%s'

(F) The given character is not a valid pack type.  See L<perlfunc/pack>.
(W pack) The given character is not a valid pack type but used to be
silently ignored.

=item Invalid type in unpack: '%s'

(F) The given character is not a valid unpack type.  See
L<perlfunc/unpack>.
(W unpack) The given character is not a valid unpack type but used to be
silently ignored.

=item Invalid version format (multiple underscores)

(F) Versions may contain at most a single underscore, which signals
that the version is a beta release.  See L<version> for the allowed
version formats.

=item Invalid version format (underscores before decimal)

(F) Versions may not contain decimals after the optional underscore.
See L<version> for the allowed version formats.

=item ioctl is not implemented

(F) Your machine apparently doesn't implement ioctl(), which is pretty
strange for a machine that supports C.

=item ioctl() on unopened %s

(W unopened) You tried ioctl() on a filehandle that was never opened.
Check you control flow and number of arguments.

=item IO::Socket::atmark not implemented on this architecture

(F) Your machine doesn't implement the sockatmark() functionality,
neither as a system call or an ioctl call (SIOCATMARK).

=item `%s' is not a code reference

(W overload) The second (fourth, sixth, ...) argument of overload::constant
needs to be a code reference. Either an anonymous subroutine, or a reference
to a subroutine.

=item `%s' is not an overloadable type

(W overload) You tried to overload a constant type the overload package is
unaware of.

=item junk on end of regexp

(P) The regular expression parser is confused.

=item Label not found for "last %s"

(F) You named a loop to break out of, but you're not currently in a loop
of that name, not even if you count where you were called from.  See
L<perlfunc/last>.

=item Label not found for "next %s"

(F) You named a loop to continue, but you're not currently in a loop of
that name, not even if you count where you were called from.  See
L<perlfunc/last>.

=item Label not found for "redo %s"

(F) You named a loop to restart, but you're not currently in a loop of
that name, not even if you count where you were called from.  See
L<perlfunc/last>.

=item leaving effective %s failed

(F) While under the C<use filetest> pragma, switching the real and
effective uids or gids failed.

=item listen() on closed socket %s

(W closed) You tried to do a listen on a closed socket.  Did you forget
to check the return value of your socket() call?  See
L<perlfunc/listen>.

=item lstat() on filehandle %s

(W io) You tried to do an lstat on a filehandle.  What did you mean
by that?  lstat() makes sense only on filenames.  (Perl did a fstat()
instead on the filehandle.)

=item Lvalue subs returning %s not implemented yet

(F) Due to limitations in the current implementation, array and hash
values cannot be returned in subroutines used in lvalue context.  See
L<perlsub/"Lvalue subroutines">.

=item Lookbehind longer than %d not implemented in regex;

marked by <-- HERE in m/%s/

(F) There is currently a limit on the length of string which lookbehind can
handle. This restriction may be eased in a future release. The <-- HERE
shows in the regular expression about where the problem was discovered.

=item Malformed PERLLIB_PREFIX

(F) An error peculiar to OS/2.  PERLLIB_PREFIX should be of the form

    prefix1;prefix2

or
    prefix1 prefix2

with nonempty prefix1 and prefix2.  If C<prefix1> is indeed a prefix of
a builtin library search path, prefix2 is substituted.  The error may
appear if components are not found, or are too long.  See
"PERLLIB_PREFIX" in L<perlos2>.

=item Malformed prototype for %s: %s

(F) You tried to use a function with a malformed prototype.  The
syntax of function prototypes is given a brief compile-time check for
obvious errors like invalid characters.  A more rigorous check is run
when the function is called.

=item Malformed UTF-8 character (%s)

Perl detected something that didn't comply with UTF-8 encoding rules.

One possible cause is that you read in data that you thought to be in
UTF-8 but it wasn't (it was for example legacy 8-bit data).  Another
possibility is careless use of utf8::upgrade().

=item Malformed UTF-16 surrogate

Perl thought it was reading UTF-16 encoded character data but while
doing it Perl met a malformed Unicode surrogate.

=item %s matches null string many times in regex;

marked by <-- HERE in m/%s/

(W regexp) The pattern you've specified would be an infinite loop if the
regular expression engine didn't specifically check for that.  The <-- HERE
shows in the regular expression about where the problem was discovered.
See L<perlre>.

=item "%s" may clash with future reserved word

(W) This warning may be due to running a perl5 script through a perl4
interpreter, especially if the word that is being warned about is
"use" or "my".

=item % may only be used in unpack

(F) You can't pack a string by supplying a checksum, because the
checksumming process loses information, and you can't go the other way.
See L<perlfunc/unpack>.

=item Method for operation %s not found in package %s during blessing

(F) An attempt was made to specify an entry in an overloading table that
doesn't resolve to a valid subroutine.  See L<overload>.

=item Method %s not permitted

See Server error.

=item Might be a runaway multi-line %s string starting on line %d

(S) An advisory indicating that the previous error may have been caused
by a missing delimiter on a string or pattern, because it eventually
ended earlier on the current line.

=item Misplaced _ in number

(W syntax) An underscore (underbar) in a numeric constant did not
separate two digits.

=item Missing %sbrace%s on \N{}

(F) Wrong syntax of character name literal C<\N{charname}> within
double-quotish context.

=item Missing comma after first argument to %s function

(F) While certain functions allow you to specify a filehandle or an
"indirect object" before the argument list, this ain't one of them.

=item Missing command in piped open

(W pipe) You used the C<open(FH, "| command")> or
C<open(FH, "command |")> construction, but the command was missing or
blank.

=item Missing name in "my sub"

(F) The reserved syntax for lexically scoped subroutines requires that
they have a name with which they can be found.

=item Missing $ on loop variable

(F) Apparently you've been programming in B<csh> too much.  Variables
are always mentioned with the $ in Perl, unlike in the shells, where it
can vary from one line to the next.

=item (Missing operator before %s?)

(S) This is an educated guess made in conjunction with the message "%s
found where operator expected".  Often the missing operator is a comma.

=item Missing right brace on %s

(F) Missing right brace in C<\p{...}> or C<\P{...}>.

=item Missing right curly or square bracket

(F) The lexer counted more opening curly or square brackets than closing
ones.  As a general rule, you'll find it's missing near the place you
were last editing.

=item (Missing semicolon on previous line?)

(S) This is an educated guess made in conjunction with the message "%s
found where operator expected".  Don't automatically put a semicolon on
the previous line just because you saw this message.

=item Modification of a read-only value attempted

(F) You tried, directly or indirectly, to change the value of a
constant.  You didn't, of course, try "2 = 1", because the compiler
catches that.  But an easy way to do the same thing is:

    sub mod { $_[0] = 1 }
    mod(2);

Another way is to assign to a substr() that's off the end of the string.

Yet another way is to assign to a C<foreach> loop I<VAR> when I<VAR>
is aliased to a constant in the look I<LIST>:

        $x = 1;
        foreach my $n ($x, 2) {
            $n *= 2; # modifies the $x, but fails on attempt to modify the 2
        }

=item Modification of non-creatable array value attempted, %s

(F) You tried to make an array value spring into existence, and the
subscript was probably negative, even counting from end of the array
backwards.

=item Modification of non-creatable hash value attempted, %s

(P) You tried to make a hash value spring into existence, and it
couldn't be created for some peculiar reason.

=item Module name must be constant

(F) Only a bare module name is allowed as the first argument to a "use".

=item Module name required with -%c option

(F) The C<-M> or C<-m> options say that Perl should load some module, but
you omitted the name of the module.  Consult L<perlrun> for full details
about C<-M> and C<-m>.

=item More than one argument to open

(F) The C<open> function has been asked to open multiple files. This
can happen if you are trying to open a pipe to a command that takes a
list of arguments, but have forgotten to specify a piped open mode.
See L<perlfunc/open> for details.

=item msg%s not implemented

(F) You don't have System V message IPC on your system.

=item Multidimensional syntax %s not supported

(W syntax) Multidimensional arrays aren't written like C<$foo[1,2,3]>.
They're written like C<$foo[1][2][3]>, as in C.

=item / must be followed by a*, A* or Z*

(F) You had a pack template indicating a counted-length string,
Currently the only things that can have their length counted are a*, A*
or Z*.  See L<perlfunc/pack>.

=item / must be followed by a, A or Z

(F) You had an unpack template indicating a counted-length string, which
must be followed by one of the letters a, A or Z to indicate what sort
of string is to be unpacked.  See L<perlfunc/pack>.

=item / must follow a numeric type

(F) You had an unpack template that contained a '#', but this did not
follow some numeric unpack specification.  See L<perlfunc/pack>.

=item "my sub" not yet implemented

(F) Lexically scoped subroutines are not yet implemented.  Don't try
that yet.

=item "my" variable %s can't be in a package

(F) Lexically scoped variables aren't in a package, so it doesn't make
sense to try to declare one with a package qualifier on the front.  Use
local() if you want to localize a package variable.

=item Name "%s::%s" used only once: possible typo

(W once) Typographical errors often show up as unique variable names.
If you had a good reason for having a unique name, then just mention it
again somehow to suppress the message.  The C<our> declaration is
provided for this purpose.

=item Negative length

(F) You tried to do a read/write/send/recv operation with a buffer
length that is less than 0.  This is difficult to imagine.

=item Negative offset to vec in lvalue context

(F) When C<vec> is called in an lvalue context, the second argument must be
greater than or equal to zero.

=item Nested quantifiers in regex; marked by <-- HERE in m/%s/

(F) You can't quantify a quantifier without intervening parentheses. So
things like ** or +* or ?* are illegal. The <-- HERE shows in the regular
expression about where the problem was discovered.

Note that the minimal matching quantifiers, C<*?>, C<+?>, and
C<??> appear to be nested quantifiers, but aren't.  See L<perlre>.

=item %s never introduced

(S internal) The symbol in question was declared but somehow went out of
scope before it could possibly have been used.

=item No %s allowed while running setuid

(F) Certain operations are deemed to be too insecure for a setuid or
setgid script to even be allowed to attempt.  Generally speaking there
will be another way to do what you want that is, if not secure, at least
securable.  See L<perlsec>.

=item No B<-e> allowed in setuid scripts

(F) A setuid script can't be specified by the user.

=item No comma allowed after %s

(F) A list operator that has a filehandle or "indirect object" is not
allowed to have a comma between that and the following arguments.
Otherwise it'd be just another one of the arguments.

One possible cause for this is that you expected to have imported a
constant to your name space with B<use> or B<import> while no such
importing took place, it may for example be that your operating system
does not support that particular constant. Hopefully you did use an
explicit import list for the constants you expect to see, please see
L<perlfunc/use> and L<perlfunc/import>. While an explicit import list
would probably have caught this error earlier it naturally does not
remedy the fact that your operating system still does not support that
constant. Maybe you have a typo in the constants of the symbol import
list of B<use> or B<import> or in the constant name at the line where
this error was triggered?

=item No command into which to pipe on command line

(F) An error peculiar to VMS.  Perl handles its own command line
redirection, and found a '|' at the end of the command line, so it
doesn't know where you want to pipe the output from this command.

=item No DB::DB routine defined

(F) The currently executing code was compiled with the B<-d> switch, but
for some reason the perl5db.pl file (or some facsimile thereof) didn't
define a routine to be called at the beginning of each statement.  Which
is odd, because the file should have been required automatically, and
should have blown up the require if it didn't parse right.

=item No dbm on this machine

(P) This is counted as an internal error, because every machine should
supply dbm nowadays, because Perl comes with SDBM.  See L<SDBM_File>.

=item No DBsub routine

(F) The currently executing code was compiled with the B<-d> switch,
but for some reason the perl5db.pl file (or some facsimile thereof)
didn't define a DB::sub routine to be called at the beginning of each
ordinary subroutine call.

=item No error file after 2> or 2>> on command line

(F) An error peculiar to VMS.  Perl handles its own command line
redirection, and found a '2>' or a '2>>' on the command line, but can't
find the name of the file to which to write data destined for stderr.

=item No input file after < on command line

(F) An error peculiar to VMS.  Perl handles its own command line
redirection, and found a '<' on the command line, but can't find the
name of the file from which to read data for stdin.

=item No #! line

(F) The setuid emulator requires that scripts have a well-formed #! line
even on machines that don't support the #! construct.

=item "no" not allowed in expression

(F) The "no" keyword is recognized and executed at compile time, and
returns no useful value.  See L<perlmod>.

=item No output file after > on command line

(F) An error peculiar to VMS.  Perl handles its own command line
redirection, and found a lone '>' at the end of the command line, so it
doesn't know where you wanted to redirect stdout.

=item No output file after > or >> on command line

(F) An error peculiar to VMS.  Perl handles its own command line
redirection, and found a '>' or a '>>' on the command line, but can't
find the name of the file to which to write data destined for stdout.

=item No package name allowed for variable %s in "our"

(F) Fully qualified variable names are not allowed in "our"
declarations, because that doesn't make much sense under existing
semantics.  Such syntax is reserved for future extensions.

=item No Perl script found in input

(F) You called C<perl -x>, but no line was found in the file beginning
with #! and containing the word "perl".

=item No setregid available

(F) Configure didn't find anything resembling the setregid() call for
your system.

=item No setreuid available

(F) Configure didn't find anything resembling the setreuid() call for
your system.

=item No space allowed after -%c

(F) The argument to the indicated command line switch must follow
immediately after the switch, without intervening spaces.

=item No %s specified for -%c

(F) The indicated command line switch needs a mandatory argument, but
you haven't specified one.

=item No such class %s

(F) You provided a class qualifier in a "my" or "our" declaration, but
this class doesn't exist at this point in your program.

=item No such pipe open

(P) An error peculiar to VMS.  The internal routine my_pclose() tried to
close a pipe which hadn't been opened.  This should have been caught
earlier as an attempt to close an unopened filehandle.

=item No such signal: SIG%s

(W signal) You specified a signal name as a subscript to %SIG that was
not recognized.  Say C<kill -l> in your shell to see the valid signal
names on your system.

=item Not a CODE reference

(F) Perl was trying to evaluate a reference to a code value (that is, a
subroutine), but found a reference to something else instead.  You can
use the ref() function to find out what kind of ref it really was.  See
also L<perlref>.

=item Not a format reference

(F) I'm not sure how you managed to generate a reference to an anonymous
format, but this indicates you did, and that it didn't exist.

=item Not a GLOB reference

(F) Perl was trying to evaluate a reference to a "typeglob" (that is, a
symbol table entry that looks like C<*foo>), but found a reference to
something else instead.  You can use the ref() function to find out what
kind of ref it really was.  See L<perlref>.

=item Not a HASH reference

(F) Perl was trying to evaluate a reference to a hash value, but found a
reference to something else instead.  You can use the ref() function to
find out what kind of ref it really was.  See L<perlref>.

=item Not an ARRAY reference

(F) Perl was trying to evaluate a reference to an array value, but found
a reference to something else instead.  You can use the ref() function
to find out what kind of ref it really was.  See L<perlref>.

=item Not a perl script

(F) The setuid emulator requires that scripts have a well-formed #! line
even on machines that don't support the #! construct.  The line must
mention perl.

=item Not a SCALAR reference

(F) Perl was trying to evaluate a reference to a scalar value, but found
a reference to something else instead.  You can use the ref() function
to find out what kind of ref it really was.  See L<perlref>.

=item Not a subroutine reference

(F) Perl was trying to evaluate a reference to a code value (that is, a
subroutine), but found a reference to something else instead.  You can
use the ref() function to find out what kind of ref it really was.  See
also L<perlref>.

=item Not a subroutine reference in overload table

(F) An attempt was made to specify an entry in an overloading table that
doesn't somehow point to a valid subroutine.  See L<overload>.

=item Not enough arguments for %s

(F) The function requires more arguments than you specified.

=item Not enough format arguments

(W syntax) A format specified more picture fields than the next line
supplied.  See L<perlform>.

=item %s: not found

(A) You've accidentally run your script through the Bourne shell instead
of Perl.  Check the #! line, or manually feed your script into Perl
yourself.

=item %s not allowed in length fields

(F) The count in the (un)pack template may be replaced by C<[TEMPLATE]> only if
C<TEMPLATE> always matches the same amount of packed bytes.  Redesign
the template.

=item no UTC offset information; assuming local time is UTC

(S) A warning peculiar to VMS.  Perl was unable to find the local
timezone offset, so it's assuming that local system time is equivalent
to UTC.  If it's not, define the logical name
F<SYS$TIMEZONE_DIFFERENTIAL> to translate to the number of seconds which
need to be added to UTC to get local time.

=item Null filename used

(F) You can't require the null filename, especially because on many
machines that means the current directory!  See L<perlfunc/require>.

=item NULL OP IN RUN

(P debugging) Some internal routine called run() with a null opcode
pointer.

=item Null picture in formline

(F) The first argument to formline must be a valid format picture
specification.  It was found to be empty, which probably means you
supplied it an uninitialized value.  See L<perlform>.

=item Null realloc

(P) An attempt was made to realloc NULL.

=item NULL regexp argument

(P) The internal pattern matching routines blew it big time.

=item NULL regexp parameter

(P) The internal pattern matching routines are out of their gourd.

=item Number too long

(F) Perl limits the representation of decimal numbers in programs to
about 250 characters.  You've exceeded that length.  Future
versions of Perl are likely to eliminate this arbitrary limitation.  In
the meantime, try using scientific notation (e.g. "1e6" instead of
"1_000_000").

=item Octal number in vector unsupported

(F) Numbers with a leading C<0> are not currently allowed in vectors.
The octal number interpretation of such numbers may be supported in a
future version.

=item Octal number > 037777777777 non-portable

(W portable) The octal number you specified is larger than 2**32-1
(4294967295) and therefore non-portable between systems.  See
L<perlport> for more on portability concerns.

See also L<perlport> for writing portable code.

=item Odd number of arguments for overload::constant

(W overload) The call to overload::constant contained an odd number of
arguments. The arguments should come in pairs.

=item Odd number of elements in anonymous hash

(W misc) You specified an odd number of elements to initialize a hash,
which is odd, because hashes come in key/value pairs.

=item Odd number of elements in hash assignment

(W misc) You specified an odd number of elements to initialize a hash,
which is odd, because hashes come in key/value pairs.

=item Offset outside string

(F) You tried to do a read/write/send/recv operation with an offset
pointing outside the buffer.  This is difficult to imagine.  The sole
exception to this is that C<sysread()>ing past the buffer will extend
the buffer and zero pad the new area.

=item -%s on unopened filehandle %s

(W unopened) You tried to invoke a file test operator on a filehandle
that isn't open.  Check your control flow.  See also L<perlfunc/-X>.

=item %s() on unopened %s

(W unopened) An I/O operation was attempted on a filehandle that was
never initialized.  You need to do an open(), a sysopen(), or a socket()
call, or call a constructor from the FileHandle package.

=item oops: oopsAV

(S internal) An internal warning that the grammar is screwed up.

=item oops: oopsHV

(S internal) An internal warning that the grammar is screwed up.

=item Operation `%s': no method found, %s

(F) An attempt was made to perform an overloaded operation for which no
handler was defined.  While some handlers can be autogenerated in terms
of other handlers, there is no default handler for any operation, unless
C<fallback> overloading key is specified to be true.  See L<overload>.

=item Operator or semicolon missing before %s

(S ambiguous) You used a variable or subroutine call where the parser
was expecting an operator.  The parser has assumed you really meant to
use an operator, but this is highly likely to be incorrect.  For
example, if you say "*foo *foo" it will be interpreted as if you said
"*foo * 'foo'".

=item "our" variable %s redeclared

(W misc) You seem to have already declared the same global once before
in the current lexical scope.

=item Out of memory!

(X) The malloc() function returned 0, indicating there was insufficient
remaining memory (or virtual memory) to satisfy the request.  Perl has
no option but to exit immediately.

=item Out of memory during "large" request for %s

(F) The malloc() function returned 0, indicating there was insufficient
remaining memory (or virtual memory) to satisfy the request. However,
the request was judged large enough (compile-time default is 64K), so a
possibility to shut down by trapping this error is granted.

=item Out of memory during request for %s

(X|F) The malloc() function returned 0, indicating there was
insufficient remaining memory (or virtual memory) to satisfy the
request.

The request was judged to be small, so the possibility to trap it
depends on the way perl was compiled.  By default it is not trappable.
However, if compiled for this, Perl may use the contents of C<$^M> as an
emergency pool after die()ing with this message.  In this case the error
is trappable I<once>, and the error message will include the line and file
where the failed request happened.

=item Out of memory during ridiculously large request

(F) You can't allocate more than 2^31+"small amount" bytes.  This error
is most likely to be caused by a typo in the Perl program. e.g.,
C<$arr[time]> instead of C<$arr[$time]>.

=item Out of memory for yacc stack

(F) The yacc parser wanted to grow its stack so it could continue
parsing, but realloc() wouldn't give it more memory, virtual or
otherwise.

=item @ outside of string

(F) You had a pack template that specified an absolute position outside
the string being unpacked.  See L<perlfunc/pack>.

=item %s package attribute may clash with future reserved word: %s

(W reserved) A lowercase attribute name was used that had a
package-specific handler.  That name might have a meaning to Perl itself
some day, even though it doesn't yet.  Perhaps you should use a
mixed-case attribute name, instead.  See L<attributes>.

=item page overflow

(W io) A single call to write() produced more lines than can fit on a
page.  See L<perlform>.

=item panic: %s

(P) An internal error.

=item panic: ck_grep

(P) Failed an internal consistency check trying to compile a grep.

=item panic: ck_split

(P) Failed an internal consistency check trying to compile a split.

=item panic: corrupt saved stack index

(P) The savestack was requested to restore more localized values than
there are in the savestack.

=item panic: del_backref

(P) Failed an internal consistency check while trying to reset a weak
reference.

=item panic: die %s

(P) We popped the context stack to an eval context, and then discovered
it wasn't an eval context.

=item panic: pp_match%s

(P) The internal pp_match() routine was called with invalid operational
data.

=item panic: do_subst

(P) The internal pp_subst() routine was called with invalid operational
data.

=item panic: do_trans_%s

(P) The internal do_trans routines were called with invalid operational
data.

=item panic: frexp

(P) The library function frexp() failed, making printf("%f") impossible.

=item panic: goto

(P) We popped the context stack to a context with the specified label,
and then discovered it wasn't a context we know how to do a goto in.

=item panic: INTERPCASEMOD

(P) The lexer got into a bad state at a case modifier.

=item panic: INTERPCONCAT

(P) The lexer got into a bad state parsing a string with brackets.

=item panic: kid popen errno read

(F) forked child returned an incomprehensible message about its errno.

=item panic: last

(P) We popped the context stack to a block context, and then discovered
it wasn't a block context.

=item panic: leave_scope clearsv

(P) A writable lexical variable became read-only somehow within the
scope.

=item panic: leave_scope inconsistency

(P) The savestack probably got out of sync.  At least, there was an
invalid enum on the top of it.

=item panic: magic_killbackrefs

(P) Failed an internal consistency check while trying to reset all weak
references to an object.

=item panic: malloc

(P) Something requested a negative number of bytes of malloc.

=item panic: mapstart

(P) The compiler is screwed up with respect to the map() function.

=item panic: null array

(P) One of the internal array routines was passed a null AV pointer.

=item panic: pad_alloc

(P) The compiler got confused about which scratch pad it was allocating
and freeing temporaries and lexicals from.

=item panic: pad_free curpad

(P) The compiler got confused about which scratch pad it was allocating
and freeing temporaries and lexicals from.

=item panic: pad_free po

(P) An invalid scratch pad offset was detected internally.

=item panic: pad_reset curpad

(P) The compiler got confused about which scratch pad it was allocating
and freeing temporaries and lexicals from.

=item panic: pad_sv po

(P) An invalid scratch pad offset was detected internally.

=item panic: pad_swipe curpad

(P) The compiler got confused about which scratch pad it was allocating
and freeing temporaries and lexicals from.

=item panic: pad_swipe po

(P) An invalid scratch pad offset was detected internally.

=item panic: pp_iter

(P) The foreach iterator got called in a non-loop context frame.

=item panic: pp_split

(P) Something terrible went wrong in setting up for the split.

=item panic: realloc

(P) Something requested a negative number of bytes of realloc.

=item panic: restartop

(P) Some internal routine requested a goto (or something like it), and
didn't supply the destination.

=item panic: return

(P) We popped the context stack to a subroutine or eval context, and
then discovered it wasn't a subroutine or eval context.

=item panic: scan_num

(P) scan_num() got called on something that wasn't a number.

=item panic: sv_insert

(P) The sv_insert() routine was told to remove more string than there
was string.

=item panic: top_env

(P) The compiler attempted to do a goto, or something weird like that.

=item panic: yylex

(P) The lexer got into a bad state while processing a case modifier.

=item panic: utf16_to_utf8: odd bytelen

(P) Something tried to call utf16_to_utf8 with an odd (as opposed
to even) byte length.

=item Parentheses missing around "%s" list

(W parenthesis) You said something like

    my $foo, $bar = @_;

when you meant

    my ($foo, $bar) = @_;

Remember that "my", "our", and "local" bind tighter than comma.

=item Perl %s required--this is only version %s, stopped

(F) The module in question uses features of a version of Perl more
recent than the currently running version.  How long has it been since
you upgraded, anyway?  See L<perlfunc/require>.

=item PERL_SH_DIR too long

(F) An error peculiar to OS/2. PERL_SH_DIR is the directory to find the
C<sh>-shell in.  See "PERL_SH_DIR" in L<perlos2>.

=item perl: warning: Setting locale failed.

(S) The whole warning message will look something like:

        perl: warning: Setting locale failed.
        perl: warning: Please check that your locale settings:
                LC_ALL = "En_US",
                LANG = (unset)
            are supported and installed on your system.
        perl: warning: Falling back to the standard locale ("C").

Exactly what were the failed locale settings varies.  In the above the
settings were that the LC_ALL was "En_US" and the LANG had no value.
This error means that Perl detected that you and/or your operating
system supplier and/or system administrator have set up the so-called
locale system but Perl could not use those settings.  This was not
dead serious, fortunately: there is a "default locale" called "C" that
Perl can and will use, the script will be run.  Before you really fix
the problem, however, you will get the same error message each time
you run Perl.  How to really fix the problem can be found in
L<perllocale> section B<LOCALE PROBLEMS>.

=item perlio: argument list not closed for layer "%s"

(W layer) When pushing a layer with arguments onto the Perl I/O system you
forgot the ) that closes the argument list.  (Layers take care of transforming
data between external and internal representations.)  Perl stopped parsing
the layer list at this point and did not attempt to push this layer.
If your program didn't explicitly request the failing operation, it may be
the result of the value of the environment variable PERLIO.

=item perlio: invalid separator character %s in layer specification list %s

(W layer) When pushing layers onto the Perl I/O system, something other than a
colon or whitespace was seen between the elements of a layer list.
If the previous attribute had a parenthesised parameter list, perhaps that
list was terminated too soon.

=item perlio: unknown layer "%s"

(W layer) An attempt was made to push an unknown layer onto the Perl I/O
system.  (Layers take care of transforming data between external and
internal representations.)  Note that some layers, such as C<mmap>,
are not supported in all environments.  If your program didn't
explicitly request the failing operation, it may be the result of the
value of the environment variable PERLIO.

=item Permission denied

(F) The setuid emulator in suidperl decided you were up to no good.

=item pid %x not a child

(W exec) A warning peculiar to VMS.  Waitpid() was asked to wait for a
process which isn't a subprocess of the current process.  While this is
fine from VMS' perspective, it's probably not what you intended.

=item P must have an explicit size

(F) The unpack format P must have an explicit size, not "*".

=item POSIX syntax [%s] belongs inside character classes in regex;

marked by <-- HERE in m/%s/

(W regexp) The character class constructs [: :], [= =], and [. .]  go
I<inside> character classes, the [] are part of the construct, for example:
/[012[:alpha:]345]/.  Note that [= =] and [. .] are not currently
implemented; they are simply placeholders for future extensions and will
cause fatal errors.  The <-- HERE shows in the regular expression about
where the problem was discovered.  See L<perlre>.

=item POSIX syntax [. .] is reserved for future extensions in regex;

marked by <-- HERE in m/%s/

(F regexp) Within regular expression character classes ([]) the syntax
beginning with "[." and ending with ".]" is reserved for future extensions.
If you need to represent those character sequences inside a regular
expression character class, just quote the square brackets with the
backslash: "\[." and ".\]".  The <-- HERE shows in the regular expression
about where the problem was discovered.  See L<perlre>.

=item POSIX syntax [= =] is reserved for future extensions in regex;

marked by <-- HERE in m/%s/

(F) Within regular expression character classes ([]) the syntax beginning
with "[=" and ending with "=]" is reserved for future extensions.  If you
need to represent those character sequences inside a regular expression
character class, just quote the square brackets with the backslash: "\[="
and "=\]".  The <-- HERE shows in the regular expression about where the
problem was discovered.  See L<perlre>.

=item POSIX class [:%s:] unknown in regex;

marked by <-- HERE in m/%s/

(F) The class in the character class [: :] syntax is unknown.  The <-- HERE
shows in the regular expression about where the problem was discovered.
Note that the POSIX character classes do B<not> have the C<is> prefix
the corresponding C interfaces have: in other words, it's C<[[:print:]]>,
not C<isprint>.  See L<perlre>.

=item POSIX getpgrp can't take an argument

(F) Your system has POSIX getpgrp(), which takes no argument, unlike
the BSD version, which takes a pid.

=item Possible attempt to put comments in qw() list

(W qw) qw() lists contain items separated by whitespace; as with literal
strings, comment characters are not ignored, but are instead treated as
literal data.  (You may have used different delimiters than the
parentheses shown here; braces are also frequently used.)

You probably wrote something like this:

    @list = qw(
        a # a comment
        b # another comment
    );

when you should have written this:

    @list = qw(
        a
        b
    );

If you really want comments, build your list the
old-fashioned way, with quotes and commas:

    @list = (
        'a',    # a comment
        'b',    # another comment
    );

=item Possible attempt to separate words with commas

(W qw) qw() lists contain items separated by whitespace; therefore
commas aren't needed to separate the items.  (You may have used
different delimiters than the parentheses shown here; braces are also
frequently used.)

You probably wrote something like this:

    qw! a, b, c !;

which puts literal commas into some of the list items.  Write it without
commas if you don't want them to appear in your data:

    qw! a b c !;

=item Possible memory corruption: %s overflowed 3rd argument

(F) An ioctl() or fcntl() returned more than Perl was bargaining for.
Perl guesses a reasonable buffer size, but puts a sentinel byte at the
end of the buffer just in case.  This sentinel byte got clobbered, and
Perl assumes that memory is now corrupted.  See L<perlfunc/ioctl>.

=item Possible precedence problem on bitwise %c operator

(W precedence) Your program uses a bitwise logical operator in conjunction
with a numeric comparison operator, like this :

    if ($x & $y == 0) { ... }

This expression is actually equivalent to C<$x & ($y == 0)>, due to the
higher precedence of C<==>. This is probably not what you want. (If you
really meant to write this, disable the warning, or, better, write
C<$x & ($y == 0 ? 1 : 0)>).

=item Possible unintended interpolation of %s in string

(W ambiguous) You said something like `@foo' in a double-quoted string
but there was no array C<@foo> in scope at the time. If you wanted a
literal @foo, then write it as \@foo; otherwise find out what happened
to the array you apparently lost track of.

=item Possible Y2K bug: %s

(W y2k) You are concatenating the number 19 with another number, which
could be a potential Year 2000 problem.

=item pragma "attrs" is deprecated, use "sub NAME : ATTRS" instead

(D deprecated) You have written something like this:

    sub doit
    {
        use attrs qw(locked);
    }

You should use the new declaration syntax instead.

    sub doit : locked
    {
        ...

The C<use attrs> pragma is now obsolete, and is only provided for
backward-compatibility. See L<perlsub/"Subroutine Attributes">.

=item Precedence problem: open %s should be open(%s)

(S precedence) The old irregular construct

    open FOO || die;

is now misinterpreted as

    open(FOO || die);

because of the strict regularization of Perl 5's grammar into unary and
list operators.  (The old open was a little of both.)  You must put
parentheses around the filehandle, or use the new "or" operator instead
of "||".

=item Premature end of script headers

See Server error.

=item printf() on closed filehandle %s

(W closed) The filehandle you're writing to got itself closed sometime
before now.  Check your control flow.

=item print() on closed filehandle %s

(W closed) The filehandle you're printing on got itself closed sometime
before now.  Check your control flow.

=item Process terminated by SIG%s

(W) This is a standard message issued by OS/2 applications, while *nix
applications die in silence.  It is considered a feature of the OS/2
port.  One can easily disable this by appropriate sighandlers, see
L<perlipc/"Signals">.  See also "Process terminated by SIGTERM/SIGINT"
in L<perlos2>.

=item Prototype mismatch: %s vs %s

(S prototype) The subroutine being declared or defined had previously been
declared or defined with a different function prototype.

=item Prototype not terminated

(F) You've omitted the closing parenthesis in a function prototype
definition.

=item Quantifier in {,} bigger than %d in regex;

marked by <-- HERE in m/%s/

(F) There is currently a limit to the size of the min and max values of the
{min,max} construct. The <-- HERE shows in the regular expression about where
the problem was discovered. See L<perlre>.

=item Quantifier unexpected on zero-length expression;

marked by <-- HERE in m/%s/

(W regexp) You applied a regular expression quantifier in a place where
it makes no sense, such as on a zero-width assertion.  Try putting the
quantifier inside the assertion instead.  For example, the way to match
"abc" provided that it is followed by three repetitions of "xyz" is
C</abc(?=(?:xyz){3})/>, not C</abc(?=xyz){3}/>.

The <-- HERE shows in the regular expression about where the problem was
discovered.

=item Range iterator outside integer range

(F) One (or both) of the numeric arguments to the range operator ".."
are outside the range which can be represented by integers internally.
One possible workaround is to force Perl to use magical string increment
by prepending "0" to your numbers.

=item read() on closed filehandle %s

(W closed) You tried to read from a closed filehandle.

=item read() on unopened filehandle %s

(W unopened) You tried to read from a filehandle that was never opened.

=item readline() on closed filehandle %s

(W closed) The filehandle you're reading from got itself closed sometime
before now.  Check your control flow.

=item Reallocation too large: %lx

(F) You can't allocate more than 64K on an MS-DOS machine.

=item realloc() of freed memory ignored

(S malloc) An internal routine called realloc() on something that had
already been freed.

=item Recompile perl with B<-D>DEBUGGING to use B<-D> switch

(F debugging) You can't use the B<-D> option unless the code to produce
the desired output is compiled into Perl, which entails some overhead,
which is why it's currently left out of your copy.

=item Recursive inheritance detected in package '%s'

(F) More than 100 levels of inheritance were used.  Probably indicates
an unintended loop in your inheritance hierarchy.

=item Recursive inheritance detected while looking for method %s

(F) More than 100 levels of inheritance were encountered while invoking
a method.  Probably indicates an unintended loop in your inheritance
hierarchy.

=item Reference found where even-sized list expected

(W misc) You gave a single reference where Perl was expecting a list
with an even number of elements (for assignment to a hash). This usually
means that you used the anon hash constructor when you meant to use
parens. In any case, a hash requires key/value B<pairs>.

    %hash = { one => 1, two => 2, };    # WRONG
    %hash = [ qw/ an anon array / ];    # WRONG
    %hash = ( one => 1, two => 2, );    # right
    %hash = qw( one 1 two 2 );                  # also fine

=item Reference is already weak

(W misc) You have attempted to weaken a reference that is already weak.
Doing so has no effect.

=item Reference miscount in sv_replace()

(W internal) The internal sv_replace() function was handed a new SV with
a reference count of other than 1.

=item Reference to nonexistent group in regex;

marked by <-- HERE in m/%s/

(F) You used something like C<\7> in your regular expression, but there are
not at least seven sets of capturing parentheses in the expression. If you
wanted to have the character with value 7 inserted into the regular expression,
prepend a zero to make the number at least two digits: C<\07>

The <-- HERE shows in the regular expression about where the problem was
discovered.

=item regexp memory corruption

(P) The regular expression engine got confused by what the regular
expression compiler gave it.

=item Regexp out of space

(P) A "can't happen" error, because safemalloc() should have caught it
earlier.

=item Repeat count in pack overflows

(F) You can't specify a repeat count so large that it overflows your
signed integers.  See L<perlfunc/pack>.

=item Repeat count in unpack overflows

(F) You can't specify a repeat count so large that it overflows your
signed integers.  See L<perlfunc/unpack>.

=item Reversed %s= operator

(W syntax) You wrote your assignment operator backwards.  The = must
always comes last, to avoid ambiguity with subsequent unary operators.

=item Runaway format

(F) Your format contained the ~~ repeat-until-blank sequence, but it
produced 200 lines at once, and the 200th line looked exactly like the
199th line.  Apparently you didn't arrange for the arguments to exhaust
themselves, either by using ^ instead of @ (for scalar variables), or by
shifting or popping (for array variables).  See L<perlform>.

=item Scalar value @%s[%s] better written as $%s[%s]

(W syntax) You've used an array slice (indicated by @) to select a
single element of an array.  Generally it's better to ask for a scalar
value (indicated by $).  The difference is that C<$foo[&bar]> always
behaves like a scalar, both when assigning to it and when evaluating its
argument, while C<@foo[&bar]> behaves like a list when you assign to it,
and provides a list context to its subscript, which can do weird things
if you're expecting only one subscript.

On the other hand, if you were actually hoping to treat the array
element as a list, you need to look into how references work, because
Perl will not magically convert between scalars and lists for you.  See
L<perlref>.

=item Scalar value @%s{%s} better written as $%s{%s}

(W syntax) You've used a hash slice (indicated by @) to select a single
element of a hash.  Generally it's better to ask for a scalar value
(indicated by $).  The difference is that C<$foo{&bar}> always behaves
like a scalar, both when assigning to it and when evaluating its
argument, while C<@foo{&bar}> behaves like a list when you assign to it,
and provides a list context to its subscript, which can do weird things
if you're expecting only one subscript.

On the other hand, if you were actually hoping to treat the hash element
as a list, you need to look into how references work, because Perl will
not magically convert between scalars and lists for you.  See
L<perlref>.

=item Scalars leaked: %d

(P) Something went wrong in Perl's internal bookkeeping of scalars:
not all scalar variables were deallocated by the time Perl exited.
What this usually indicates is a memory leak, which is of course bad,
especially if the Perl program is intended to be long-running.

=item Script is not setuid/setgid in suidperl

(F) Oddly, the suidperl program was invoked on a script without a setuid
or setgid bit set.  This doesn't make much sense.

=item Search pattern not terminated

(F) The lexer couldn't find the final delimiter of a // or m{}
construct.  Remember that bracketing delimiters count nesting level.
Missing the leading C<$> from a variable C<$m> may cause this error.

Note that since Perl 5.9.0 a // can also be the I<defined-or>
construct, not just the empty search pattern.  Therefore code written
in Perl 5.9.0 or later that uses the // as the I<defined-or> can be
misparsed by pre-5.9.0 Perls as a non-terminated search pattern.

=item %sseek() on unopened filehandle

(W unopened) You tried to use the seek() or sysseek() function on a
filehandle that was either never opened or has since been closed.

=item select not implemented

(F) This machine doesn't implement the select() system call.

=item Self-ties of arrays and hashes are not supported

(F) Self-ties are of arrays and hashes are not supported in
the current implementation.

=item Semicolon seems to be missing

(W semicolon) A nearby syntax error was probably caused by a missing
semicolon, or possibly some other missing operator, such as a comma.

=item semi-panic: attempt to dup freed string

(S internal) The internal newSVsv() routine was called to duplicate a
scalar that had previously been marked as free.

=item sem%s not implemented

(F) You don't have System V semaphore IPC on your system.

=item send() on closed socket %s

(W closed) The socket you're sending to got itself closed sometime
before now.  Check your control flow.

=item Sequence (? incomplete in regex; marked by <-- HERE in m/%s/

(F) A regular expression ended with an incomplete extension (?. The <-- HERE
shows in the regular expression about where the problem was discovered. See
L<perlre>.

=item Sequence (?{...}) not terminated or not {}-balanced in regex;

marked by <-- HERE in m/%s/

(F) If the contents of a (?{...}) clause contains braces, they must balance
for Perl to properly detect the end of the clause. The <-- HERE shows in
the regular expression about where the problem was discovered. See
L<perlre>.

=item Sequence (?%s...) not implemented in regex;

marked by <-- HERE in m/%s/

(F) A proposed regular expression extension has the character reserved but
has not yet been written. The <-- HERE shows in the regular expression about
where the problem was discovered. See L<perlre>.

=item Sequence (?%s...) not recognized in regex;

marked by <-- HERE in m/%s/

(F) You used a regular expression extension that doesn't make sense.  The
<-- HERE shows in the regular expression about where the problem was
discovered.  See L<perlre>.

=item Sequence (?#... not terminated in regex;

marked by <-- HERE in m/%s/

(F) A regular expression comment must be terminated by a closing
parenthesis.  Embedded parentheses aren't allowed.  The <-- HERE shows in
the regular expression about where the problem was discovered. See
L<perlre>.

=item 500 Server error

See Server error.

=item Server error

This is the error message generally seen in a browser window when trying
to run a CGI program (including SSI) over the web. The actual error text
varies widely from server to server. The most frequently-seen variants
are "500 Server error", "Method (something) not permitted", "Document
contains no data", "Premature end of script headers", and "Did not
produce a valid header".

B<This is a CGI error, not a Perl error>.

You need to make sure your script is executable, is accessible by the
user CGI is running the script under (which is probably not the user
account you tested it under), does not rely on any environment variables
(like PATH) from the user it isn't running under, and isn't in a
location where the CGI server can't find it, basically, more or less.
Please see the following for more information:

        http://www.perl.org/CGI_MetaFAQ.html
        http://www.htmlhelp.org/faq/cgifaq.html
        http://www.w3.org/Security/Faq/

You should also look at L<perlfaq9>.

=item setegid() not implemented

(F) You tried to assign to C<$)>, and your operating system doesn't
support the setegid() system call (or equivalent), or at least Configure
didn't think so.

=item seteuid() not implemented

(F) You tried to assign to C<< $> >>, and your operating system doesn't
support the seteuid() system call (or equivalent), or at least Configure
didn't think so.

=item setpgrp can't take arguments

(F) Your system has the setpgrp() from BSD 4.2, which takes no
arguments, unlike POSIX setpgid(), which takes a process ID and process
group ID.

=item setrgid() not implemented

(F) You tried to assign to C<$(>, and your operating system doesn't
support the setrgid() system call (or equivalent), or at least Configure
didn't think so.

=item setruid() not implemented

(F) You tried to assign to C<$<>, and your operating system doesn't
support the setruid() system call (or equivalent), or at least Configure
didn't think so.

=item setsockopt() on closed socket %s

(W closed) You tried to set a socket option on a closed socket.  Did you
forget to check the return value of your socket() call?  See
L<perlfunc/setsockopt>.

=item Setuid/gid script is writable by world

(F) The setuid emulator won't run a script that is writable by the
world, because the world might have written on it already.

=item shm%s not implemented

(F) You don't have System V shared memory IPC on your system.

=item <> should be quotes

(F) You wrote C<< require <file> >> when you should have written
C<require 'file'>.

=item /%s/ should probably be written as "%s"

(W syntax) You have used a pattern where Perl expected to find a string,
as in the first argument to C<join>.  Perl will treat the true or false
result of matching the pattern against $_ as the string, which is
probably not what you had in mind.

=item shutdown() on closed socket %s

(W closed) You tried to do a shutdown on a closed socket.  Seems a bit
superfluous.

=item SIG%s handler "%s" not defined

(W signal) The signal handler named in %SIG doesn't, in fact, exist.
Perhaps you put it into the wrong package?

=item sort is now a reserved word

(F) An ancient error message that almost nobody ever runs into anymore.
But before sort was a keyword, people sometimes used it as a filehandle.

=item Sort subroutine didn't return a numeric value

(F) A sort comparison routine must return a number.  You probably blew
it by not using C<< <=> >> or C<cmp>, or by not using them correctly.
See L<perlfunc/sort>.

=item Sort subroutine didn't return single value

(F) A sort comparison subroutine may not return a list value with more
or less than one element.  See L<perlfunc/sort>.

=item splice() offset past end of array

(W misc) You attempted to specify an offset that was past the end of
the array passed to splice(). Splicing will instead commence at the end
of the array, rather than past it. If this isn't what you want, try
explicitly pre-extending the array by assigning $#array = $offset. See
L<perlfunc/splice>.

=item Split loop

(P) The split was looping infinitely.  (Obviously, a split shouldn't
iterate more times than there are characters of input, which is what
happened.) See L<perlfunc/split>.

=item Statement unlikely to be reached

(W exec) You did an exec() with some statement after it other than a
die().  This is almost always an error, because exec() never returns
unless there was a failure.  You probably wanted to use system()
instead, which does return.  To suppress this warning, put the exec() in
a block by itself.

=item stat() on unopened filehandle %s

(W unopened) You tried to use the stat() function on a filehandle that
was either never opened or has since been closed.

=item Stub found while resolving method `%s' overloading %s

(P) Overloading resolution over @ISA tree may be broken by importation
stubs.  Stubs should never be implicitly created, but explicit calls to
C<can> may break this.

=item Subroutine %s redefined

(W redefine) You redefined a subroutine.  To suppress this warning, say

    {
        no warnings 'redefine';
        eval "sub name { ... }";
    }

=item Substitution loop

(P) The substitution was looping infinitely.  (Obviously, a substitution
shouldn't iterate more times than there are characters of input, which
is what happened.)  See the discussion of substitution in
L<perlop/"Quote and Quote-like Operators">.

=item Substitution pattern not terminated

(F) The lexer couldn't find the interior delimiter of an s/// or s{}{}
construct.  Remember that bracketing delimiters count nesting level.
Missing the leading C<$> from variable C<$s> may cause this error.

=item Substitution replacement not terminated

(F) The lexer couldn't find the final delimiter of an s/// or s{}{}
construct.  Remember that bracketing delimiters count nesting level.
Missing the leading C<$> from variable C<$s> may cause this error.

=item substr outside of string

(W substr),(F) You tried to reference a substr() that pointed outside of
a string.  That is, the absolute value of the offset was larger than the
length of the string.  See L<perlfunc/substr>.  This warning is fatal if
substr is used in an lvalue context (as the left hand side of an
assignment or as a subroutine argument for example).

=item suidperl is no longer needed since %s

(F) Your Perl was compiled with B<-D>SETUID_SCRIPTS_ARE_SECURE_NOW, but
a version of the setuid emulator somehow got run anyway.

=item Switch (?(condition)... contains too many branches in regex;

marked by <-- HERE in m/%s/

(F) A (?(condition)if-clause|else-clause) construct can have at most two
branches (the if-clause and the else-clause). If you want one or both to
contain alternation, such as using C<this|that|other>, enclose it in
clustering parentheses:

    (?(condition)(?:this|that|other)|else-clause)

The <-- HERE shows in the regular expression about where the problem was
discovered. See L<perlre>.

=item Switch condition not recognized in regex;

marked by <-- HERE in m/%s/

(F) If the argument to the (?(...)if-clause|else-clause) construct is a
number, it can be only a number. The <-- HERE shows in the regular expression
about where the problem was discovered. See L<perlre>.

=item switching effective %s is not implemented

(F) While under the C<use filetest> pragma, we cannot switch the real
and effective uids or gids.

=item syntax error

(F) Probably means you had a syntax error.  Common reasons include:

    A keyword is misspelled.
    A semicolon is missing.
    A comma is missing.
    An opening or closing parenthesis is missing.
    An opening or closing brace is missing.
    A closing quote is missing.

Often there will be another error message associated with the syntax
error giving more information.  (Sometimes it helps to turn on B<-w>.)
The error message itself often tells you where it was in the line when
it decided to give up.  Sometimes the actual error is several tokens
before this, because Perl is good at understanding random input.
Occasionally the line number may be misleading, and once in a blue moon
the only way to figure out what's triggering the error is to call
C<perl -c> repeatedly, chopping away half the program each time to see
if the error went away.  Sort of the cybernetic version of S<20
questions>.

=item syntax error at line %d: `%s' unexpected

(A) You've accidentally run your script through the Bourne shell instead
of Perl.  Check the #! line, or manually feed your script into Perl
yourself.

=item syntax error in file %s at line %d, next 2 tokens "%s"

(F) This error is likely to occur if you run a perl5 script through
a perl4 interpreter, especially if the next 2 tokens are "use strict"
or "my $var" or "our $var".

=item %s syntax OK

(F) The final summary message when a C<perl -c> succeeds.

=item sysread() on closed filehandle %s

(W closed) You tried to read from a closed filehandle.

=item sysread() on unopened filehandle %s

(W unopened) You tried to read from a filehandle that was never opened.

=item System V %s is not implemented on this machine

(F) You tried to do something with a function beginning with "sem",
"shm", or "msg" but that System V IPC is not implemented in your
machine.  In some machines the functionality can exist but be
unconfigured.  Consult your system support.

=item syswrite() on closed filehandle %s

(W closed) The filehandle you're writing to got itself closed sometime
before now.  Check your control flow.

=item Target of goto is too deeply nested

(F) You tried to use C<goto> to reach a label that was too deeply nested
for Perl to reach.  Perl is doing you a favor by refusing.

=item tell() on unopened filehandle

(W unopened) You tried to use the tell() function on a filehandle that
was either never opened or has since been closed.

=item That use of $[ is unsupported

(F) Assignment to C<$[> is now strictly circumscribed, and interpreted
as a compiler directive.  You may say only one of

    $[ = 0;
    $[ = 1;
    ...
    local $[ = 0;
    local $[ = 1;
    ...

This is to prevent the problem of one module changing the array base out
from under another module inadvertently.  See L<perlvar/$[>.

=item The crypt() function is unimplemented due to excessive paranoia

(F) Configure couldn't find the crypt() function on your machine,
probably because your vendor didn't supply it, probably because they
think the U.S. Government thinks it's a secret, or at least that they
will continue to pretend that it is.  And if you quote me on that, I
will deny it.

=item The %s function is unimplemented

The function indicated isn't implemented on this architecture, according
to the probings of Configure.

=item The stat preceding %s wasn't an lstat

(F) It makes no sense to test the current stat buffer for symbolic
linkhood if the last stat that wrote to the stat buffer already went
past the symlink to get to the real file.  Use an actual filename
instead.

=item This Perl can't reset CRTL environ elements (%s)

=item This Perl can't set CRTL environ elements (%s=%s)

(W internal) Warnings peculiar to VMS.  You tried to change or delete an
element of the CRTL's internal environ array, but your copy of Perl
wasn't built with a CRTL that contained the setenv() function.  You'll
need to rebuild Perl with a CRTL that does, or redefine
F<PERL_ENV_TABLES> (see L<perlvms>) so that the environ array isn't the
target of the change to
%ENV which produced the warning.

=item thread failed to start: %s

(F) The entry point function of threads->create() failed for some reason.

=item times not implemented

(F) Your version of the C library apparently doesn't do times().  I
suspect you're not running on Unix.

=item Too few args to syscall

(F) There has to be at least one argument to syscall() to specify the
system call to call, silly dilly.

=item Too late for "B<-T>" option

(X) The #! line (or local equivalent) in a Perl script contains the
B<-T> option, but Perl was not invoked with B<-T> in its command line.
This is an error because, by the time Perl discovers a B<-T> in a
script, it's too late to properly taint everything from the environment.
So Perl gives up.

If the Perl script is being executed as a command using the #!
mechanism (or its local equivalent), this error can usually be fixed by
editing the #! line so that the B<-T> option is a part of Perl's first
argument: e.g. change C<perl -n -T> to C<perl -T -n>.

If the Perl script is being executed as C<perl scriptname>, then the
B<-T> option must appear on the command line: C<perl -T scriptname>.

=item Too late for "-%s" option

(X) The #! line (or local equivalent) in a Perl script contains the
B<-M> or B<-m> option.  This is an error because B<-M> and B<-m> options
are not intended for use inside scripts.  Use the C<use> pragma instead.

=item Too late to run %s block

(W void) A CHECK or INIT block is being defined during run time proper,
when the opportunity to run them has already passed.  Perhaps you are
loading a file with C<require> or C<do> when you should be using C<use>
instead.  Or perhaps you should put the C<require> or C<do> inside a
BEGIN block.

=item Too many args to syscall

(F) Perl supports a maximum of only 14 args to syscall().

=item Too many arguments for %s

(F) The function requires fewer arguments than you specified.

=item Too many )'s

=item Too many ('s

(A) You've accidentally run your script through B<csh> instead of Perl.
Check the #! line, or manually feed your script into Perl yourself.

=item Trailing \ in regex m/%s/

(F) The regular expression ends with an unbackslashed backslash.
Backslash it.   See L<perlre>.

=item Transliteration pattern not terminated

(F) The lexer couldn't find the interior delimiter of a tr/// or tr[][]
or y/// or y[][] construct.  Missing the leading C<$> from variables
C<$tr> or C<$y> may cause this error.

=item Transliteration replacement not terminated

(F) The lexer couldn't find the final delimiter of a tr/// or tr[][]
construct.

=item truncate not implemented

(F) Your machine doesn't implement a file truncation mechanism that
Configure knows about.

=item Type of arg %d to %s must be %s (not %s)

(F) This function requires the argument in that position to be of a
certain type.  Arrays must be @NAME or C<@{EXPR}>.  Hashes must be
%NAME or C<%{EXPR}>.  No implicit dereferencing is allowed--use the
{EXPR} forms as an explicit dereference.  See L<perlref>.

=item umask not implemented

(F) Your machine doesn't implement the umask function and you tried to
use it to restrict permissions for yourself (EXPR & 0700).

=item Unable to create sub named "%s"

(F) You attempted to create or access a subroutine with an illegal name.

=item Unbalanced context: %d more PUSHes than POPs

(W internal) The exit code detected an internal inconsistency in how
many execution contexts were entered and left.

=item Unbalanced saves: %d more saves than restores

(W internal) The exit code detected an internal inconsistency in how
many values were temporarily localized.

=item Unbalanced scopes: %d more ENTERs than LEAVEs

(W internal) The exit code detected an internal inconsistency in how
many blocks were entered and left.

=item Unbalanced tmps: %d more allocs than frees

(W internal) The exit code detected an internal inconsistency in how
many mortal scalars were allocated and freed.

=item Undefined format "%s" called

(F) The format indicated doesn't seem to exist.  Perhaps it's really in
another package?  See L<perlform>.

=item Undefined sort subroutine "%s" called

(F) The sort comparison routine specified doesn't seem to exist.
Perhaps it's in a different package?  See L<perlfunc/sort>.

=item Undefined subroutine &%s called

(F) The subroutine indicated hasn't been defined, or if it was, it has
since been undefined.

=item Undefined subroutine called

(F) The anonymous subroutine you're trying to call hasn't been defined,
or if it was, it has since been undefined.

=item Undefined subroutine in sort

(F) The sort comparison routine specified is declared but doesn't seem
to have been defined yet.  See L<perlfunc/sort>.

=item Undefined top format "%s" called

(F) The format indicated doesn't seem to exist.  Perhaps it's really in
another package?  See L<perlform>.

=item Undefined value assigned to typeglob

(W misc) An undefined value was assigned to a typeglob, a la
C<*foo = undef>.  This does nothing.  It's possible that you really mean
C<undef *foo>.

=item %s: Undefined variable

(A) You've accidentally run your script through B<csh> instead of Perl.
Check the #! line, or manually feed your script into Perl yourself.

=item unexec of %s into %s failed!

(F) The unexec() routine failed for some reason.  See your local FSF
representative, who probably put it there in the first place.

=item Unicode character %s is illegal

(W utf8) Certain Unicode characters have been designated off-limits by
the Unicode standard and should not be generated.  If you really know
what you are doing you can turn off this warning by C<no warnings 'utf8';>.

=item Unknown BYTEORDER

(F) There are no byte-swapping functions for a machine with this byte
order.

=item Unknown "re" subpragma '%s' (known ones are: %s)

You tried to use an unknown subpragma of the "re" pragma.

=item Unknown switch condition (?(%.2s in regex;

marked by <-- HERE in m/%s/

(F) The condition part of a (?(condition)if-clause|else-clause) construct
is not known. The condition may be lookahead or lookbehind (the condition
is true if the lookahead or lookbehind is true), a (?{...})  construct (the
condition is true if the code evaluates to a true value), or a number (the
condition is true if the set of capturing parentheses named by the number
matched).

The <-- HERE shows in the regular expression about where the problem was
discovered.  See L<perlre>.

=item Unknown open() mode '%s'

(F) The second argument of 3-argument open() is not among the list
of valid modes: C<< < >>, C<< > >>, C<<< >> >>>, C<< +< >>,
C<< +> >>, C<<< +>> >>>, C<-|>, C<|->, C<< <& >>, C<< >& >>.

=item Unknown process %x sent message to prime_env_iter: %s

(P) An error peculiar to VMS.  Perl was reading values for %ENV before
iterating over it, and someone else stuck a message in the stream of
data Perl expected.  Someone's very confused, or perhaps trying to
subvert Perl's population of %ENV for nefarious purposes.

=item Unknown warnings category '%s'

(F) An error issued by the C<warnings> pragma. You specified a warnings
category that is unknown to perl at this point.

Note that if you want to enable a warnings category registered by a module
(e.g. C<use warnings 'File::Find'>), you must have imported this module
first.

=item unmatched [ in regex; marked by <-- HERE in m/%s/

(F) The brackets around a character class must match. If you wish to
include a closing bracket in a character class, backslash it or put it
first. The <-- HERE shows in the regular expression about where the problem
was discovered. See L<perlre>.

=item unmatched ( in regex; marked by <-- HERE in m/%s/

(F) Unbackslashed parentheses must always be balanced in regular
expressions. If you're a vi user, the % key is valuable for finding the
matching parenthesis. The <-- HERE shows in the regular expression about
where the problem was discovered. See L<perlre>.

=item Unmatched right %s bracket

(F) The lexer counted more closing curly or square brackets than opening
ones, so you're probably missing a matching opening bracket.  As a
general rule, you'll find the missing one (so to speak) near the place
you were last editing.

=item Unquoted string "%s" may clash with future reserved word

(W reserved) You used a bareword that might someday be claimed as a
reserved word.  It's best to put such a word in quotes, or capitalize it
somehow, or insert an underbar into it.  You might also declare it as a
subroutine.

=item Unrecognized character %s

(F) The Perl parser has no idea what to do with the specified character
in your Perl script (or eval).  Perhaps you tried to run a compressed
script, a binary program, or a directory as a Perl program.

=item /%s/: Unrecognized escape \\%c in character class passed through

(W regexp) You used a backslash-character combination which is not
recognized by Perl inside character classes.  The character was
understood literally.

=item Unrecognized escape \\%c passed through in regex;

marked by <-- HERE in m/%s/

(W regexp) You used a backslash-character combination which is not
recognized by Perl. This combination appears in an interpolated variable or
a C<'>-delimited regular expression. The character was understood
literally. The <-- HERE shows in the regular expression about where the
escape was discovered.

=item Unrecognized escape \\%c passed through

(W misc) You used a backslash-character combination which is not
recognized by Perl.

=item Unrecognized signal name "%s"

(F) You specified a signal name to the kill() function that was not
recognized.  Say C<kill -l> in your shell to see the valid signal names
on your system.

=item Unrecognized switch: -%s  (-h will show valid options)

(F) You specified an illegal option to Perl.  Don't do that.  (If you
think you didn't do that, check the #! line to see if it's supplying the
bad switch on your behalf.)

=item Unsuccessful %s on filename containing newline

(W newline) A file operation was attempted on a filename, and that
operation failed, PROBABLY because the filename contained a newline,
PROBABLY because you forgot to chomp() it off.  See L<perlfunc/chomp>.

=item Unsupported directory function "%s" called

(F) Your machine doesn't support opendir() and readdir().

=item Unsupported function %s

(F) This machine doesn't implement the indicated function, apparently.
At least, Configure doesn't think so.

=item Unsupported function fork

(F) Your version of executable does not support forking.

Note that under some systems, like OS/2, there may be different flavors
of Perl executables, some of which may support fork, some not. Try
changing the name you call Perl by to C<perl_>, C<perl__>, and so on.

=item Unsupported script encoding

(F) Your program file begins with a Unicode Byte Order Mark (BOM) which
declares it to be in a Unicode encoding that Perl cannot yet read.

=item Unsupported socket function "%s" called

(F) Your machine doesn't support the Berkeley socket mechanism, or at
least that's what Configure thought.

=item Unterminated attribute list

(F) The lexer found something other than a simple identifier at the
start of an attribute, and it wasn't a semicolon or the start of a
block.  Perhaps you terminated the parameter list of the previous
attribute too soon.  See L<attributes>.

=item Unterminated attribute parameter in attribute list

(F) The lexer saw an opening (left) parenthesis character while parsing
an attribute list, but the matching closing (right) parenthesis
character was not found.  You may need to add (or remove) a backslash
character to get your parentheses to balance.  See L<attributes>.

=item Unterminated compressed integer

(F) An argument to unpack("w",...) was incompatible with the BER
compressed integer format and could not be converted to an integer.
See L<perlfunc/pack>.

=item Unterminated <> operator

(F) The lexer saw a left angle bracket in a place where it was expecting
a term, so it's looking for the corresponding right angle bracket, and
not finding it.  Chances are you left some needed parentheses out
earlier in the line, and you really meant a "less than".

=item untie attempted while %d inner references still exist

(W untie) A copy of the object returned from C<tie> (or C<tied>) was
still valid when C<untie> was called.

=item Useless (?%s) - use /%s modifier in regex;

marked by <-- HERE in m/%s/

(W regexp) You have used an internal modifier such as (?o) that has no
meaning unless applied to the entire regexp:

    if ($string =~ /(?o)$pattern/) { ... }

must be written as

    if ($string =~ /$pattern/o) { ... }

The <-- HERE shows in the regular expression about
where the problem was discovered. See L<perlre>.

=item Useless (?-%s) - don't use /%s modifier in regex;

marked by <-- HERE in m/%s/

(W regexp) You have used an internal modifier such as (?-o) that has no
meaning unless removed from the entire regexp:

    if ($string =~ /(?-o)$pattern/o) { ... }

must be written as

    if ($string =~ /$pattern/) { ... }

The <-- HERE shows in the regular expression about
where the problem was discovered. See L<perlre>.

=item Useless use of %s in void context

(W void) You did something without a side effect in a context that does
nothing with the return value, such as a statement that doesn't return a
value from a block, or the left side of a scalar comma operator.  Very
often this points not to stupidity on your part, but a failure of Perl
to parse your program the way you thought it would.  For example, you'd
get this if you mixed up your C precedence with Python precedence and
said

    $one, $two = 1, 2;

when you meant to say

    ($one, $two) = (1, 2);

Another common error is to use ordinary parentheses to construct a list
reference when you should be using square or curly brackets, for
example, if you say

    $array = (1,2);

when you should have said

    $array = [1,2];

The square brackets explicitly turn a list value into a scalar value,
while parentheses do not.  So when a parenthesized list is evaluated in
a scalar context, the comma is treated like C's comma operator, which
throws away the left argument, which is not what you want.  See
L<perlref> for more on this.

This warning will not be issued for numerical constants equal to 0 or 1
since they are often used in statements like

    1 while sub_with_side_effects() ;

String constants that would normally evaluate to 0 or 1 are warned
about.

=item Useless use of "re" pragma

(W) You did C<use re;> without any arguments.   That isn't very useful.

=item Useless use of sort in scalar context

(W void) You used sort in scalar context, as in :

    my $x = sort @y;

This is not very useful, and perl currently optimizes this away.

=item Useless use of %s with no values

(W syntax) You used the push() or unshift() function with no arguments
apart from the array, like C<push(@x)> or C<unshift(@foo)>. That won't
usually have any effect on the array, so is completely useless. It's
possible in principle that push(@tied_array) could have some effect
if the array is tied to a class which implements a PUSH method. If so,
you can write it as C<push(@tied_array,())> to avoid this warning.

=item "use" not allowed in expression

(F) The "use" keyword is recognized and executed at compile time, and
returns no useful value.  See L<perlmod>.

=item Use of bare << to mean <<"" is deprecated

(D deprecated) You are now encouraged to use the explicitly quoted form
if you wish to use an empty line as the terminator of the here-document.

=item Use of /c modifier is meaningless in s///

(W regexp) You used the /c modifier in a substitution.  The /c
modifier is not presently meaningful in substitutions.

=item Use of /c modifier is meaningless without /g

(W regexp) You used the /c modifier with a regex operand, but didn't
use the /g modifier.  Currently, /c is meaningful only when /g is
used.  (This may change in the future.)

=item Use of /g modifier is meaningless in split

(W regexp) You used the /g modifier on the pattern for a C<split>
operator.  Since C<split> always tries to match the pattern
repeatedly, the C</g> has no effect.

=item Use of *glob{FILEHANDLE} is deprecated

(D deprecated) You are now encouraged to use the shorter *glob{IO} form
to access the filehandle slot within a typeglob.

=item Use of chdir('') or chdir(undef) as chdir() deprecated

(D deprecated) chdir() with no arguments is documented to change to
$ENV{HOME} or $ENV{LOGDIR}.  chdir(undef) and chdir('') share this
behavior, but that has been deprecated.  In future versions they
will simply fail.

Be careful to check that what you pass to chdir() is defined and not
blank, else you might find yourself in your home directory.

=item Use of implicit split to @_ is deprecated

(D deprecated) It makes a lot of work for the compiler when you clobber
a subroutine's argument list, so it's better if you assign the results
of a split() explicitly to an array (or list).

=item Use of inherited AUTOLOAD for non-method %s() is deprecated

(D deprecated) As an (ahem) accidental feature, C<AUTOLOAD> subroutines
are looked up as methods (using the C<@ISA> hierarchy) even when the
subroutines to be autoloaded were called as plain functions (e.g.
C<Foo::bar()>), not as methods (e.g. C<< Foo->bar() >> or C<<
$obj->bar() >>).

This bug will be rectified in future by using method lookup only for
methods' C<AUTOLOAD>s.  However, there is a significant base of existing
code that may be using the old behavior.  So, as an interim step, Perl
currently issues an optional warning when non-methods use inherited
C<AUTOLOAD>s.

The simple rule is:  Inheritance will not work when autoloading
non-methods.  The simple fix for old code is:  In any module that used
to depend on inheriting C<AUTOLOAD> for non-methods from a base class
named C<BaseClass>, execute C<*AUTOLOAD = \&BaseClass::AUTOLOAD> during
startup.

In code that currently says C<use AutoLoader; @ISA = qw(AutoLoader);>
you should remove AutoLoader from @ISA and change C<use AutoLoader;> to
C<use AutoLoader 'AUTOLOAD';>.

=item Use of -l on filehandle %s

(W io) A filehandle represents an opened file, and when you opened the file
it already went past any symlink you are presumably trying to look for.
The operation returned C<undef>.  Use a filename instead.

=item Use of "package" with no arguments is deprecated

(D deprecated) You used the C<package> keyword without specifying a package
name. So no namespace is current at all. Using this can cause many
otherwise reasonable constructs to fail in baffling ways. C<use strict;>
instead.

=item Use of %s in printf format not supported

(F) You attempted to use a feature of printf that is accessible from
only C.  This usually means there's a better way to do it in Perl.

=item Use of $* is deprecated

(D deprecated) This variable magically turned on multi-line pattern
matching, both for you and for any luckless subroutine that you happen
to call.  You should use the new C<//m> and C<//s> modifiers now to do
that without the dangerous action-at-a-distance effects of C<$*>.

=item Use of %s is deprecated

(D deprecated) The construct indicated is no longer recommended for use,
generally because there's a better way to do it, and also because the
old way has bad side effects.

=item Use of $# is deprecated

(D deprecated) This was an ill-advised attempt to emulate a poorly
defined B<awk> feature.  Use an explicit printf() or sprintf() instead.

=item Use of reference "%s" as array index

(W misc) You tried to use a reference as an array index; this probably
isn't what you mean, because references in numerical context tend
to be huge numbers, and so usually indicates programmer error.

If you really do mean it, explicitly numify your reference, like so:
C<$array[0+$ref]>.  This warning is not given for overloaded objects,
either, because you can overload the numification and stringification
operators and then you assumedly know what you are doing.

=item Use of reserved word "%s" is deprecated

(D deprecated) The indicated bareword is a reserved word.  Future
versions of perl may use it as a keyword, so you're better off either
explicitly quoting the word in a manner appropriate for its context of
use, or using a different name altogether.  The warning can be
suppressed for subroutine names by either adding a C<&> prefix, or using
a package qualifier, e.g. C<&our()>, or C<Foo::our()>.

=item Use of tainted arguments in %s is deprecated

(W taint, deprecated) You have supplied C<system()> or C<exec()> with multiple
arguments and at least one of them is tainted.  This used to be allowed
but will become a fatal error in a future version of perl.  Untaint your
arguments.  See L<perlsec>.

=item Use of uninitialized value%s

(W uninitialized) An undefined value was used as if it were already
defined.  It was interpreted as a "" or a 0, but maybe it was a mistake.
To suppress this warning assign a defined value to your variables.

To help you figure out what was undefined, perl tells you what operation
you used the undefined value in.  Note, however, that perl optimizes your
program and the operation displayed in the warning may not necessarily
appear literally in your program.  For example, C<"that $foo"> is
usually optimized into C<"that " . $foo>, and the warning will refer to
the C<concatenation (.)> operator, even though there is no C<.> in your
program.

=item Using a hash as a reference is deprecated

(D deprecated) You tried to use a hash as a reference, as in
C<< %foo->{"bar"} >> or C<< %$ref->{"hello"} >>.  Versions of perl <= 5.6.1
used to allow this syntax, but shouldn't have. It is now deprecated, and will
be removed in a future version.

=item Using an array as a reference is deprecated

(D deprecated) You tried to use an array as a reference, as in
C<< @foo->[23] >> or C<< @$ref->[99] >>.  Versions of perl <= 5.6.1 used to
allow this syntax, but shouldn't have. It is now deprecated, and will be
removed in a future version.

=item UTF-16 surrogate %s

(W utf8) You tried to generate half of an UTF-16 surrogate by
requesting a Unicode character between the code points 0xD800 and
0xDFFF (inclusive).  That range is reserved exclusively for the use of
UTF-16 encoding (by having two 16-bit UCS-2 characters); but Perl
encodes its characters in UTF-8, so what you got is a very illegal
character.  If you really know what you are doing you can turn off
this warning by C<no warnings 'utf8';>.

=item Value of %s can be "0"; test with defined()

(W misc) In a conditional expression, you used <HANDLE>, <*> (glob),
C<each()>, or C<readdir()> as a boolean value.  Each of these constructs
can return a value of "0"; that would make the conditional expression
false, which is probably not what you intended.  When using these
constructs in conditional expressions, test their values with the
C<defined> operator.

=item Value of CLI symbol "%s" too long

(W misc) A warning peculiar to VMS.  Perl tried to read the value of an
%ENV element from a CLI symbol table, and found a resultant string
longer than 1024 characters.  The return value has been truncated to
1024 characters.

=item Variable "%s" is not imported%s

(F) While "use strict" in effect, you referred to a global variable that
you apparently thought was imported from another module, because
something else of the same name (usually a subroutine) is exported by
that module.  It usually means you put the wrong funny character on the
front of your variable.

=item "%s" variable %s masks earlier declaration in same %s

(W misc) A "my" or "our" variable has been redeclared in the current
scope or statement, effectively eliminating all access to the previous
instance.  This is almost always a typographical error.  Note that the
earlier variable will still exist until the end of the scope or until
all closure referents to it are destroyed.

=item Variable "%s" may be unavailable

(W closure) An inner (nested) I<anonymous> subroutine is inside a
I<named> subroutine, and outside that is another subroutine; and the
anonymous (innermost) subroutine is referencing a lexical variable
defined in the outermost subroutine.  For example:

   sub outermost { my $a; sub middle { sub { $a } } }

If the anonymous subroutine is called or referenced (directly or
indirectly) from the outermost subroutine, it will share the variable as
you would expect.  But if the anonymous subroutine is called or
referenced when the outermost subroutine is not active, it will see the
value of the shared variable as it was before and during the *first*
call to the outermost subroutine, which is probably not what you want.

In these circumstances, it is usually best to make the middle subroutine
anonymous, using the C<sub {}> syntax.  Perl has specific support for
shared variables in nested anonymous subroutines; a named subroutine in
between interferes with this feature.

=item Variable syntax

(A) You've accidentally run your script through B<csh> instead
of Perl.  Check the #! line, or manually feed your script into
Perl yourself.

=item Variable "%s" will not stay shared

(W closure) An inner (nested) I<named> subroutine is referencing a
lexical variable defined in an outer subroutine.

When the inner subroutine is called, it will probably see the value of
the outer subroutine's variable as it was before and during the *first*
call to the outer subroutine; in this case, after the first call to the
outer subroutine is complete, the inner and outer subroutines will no
longer share a common value for the variable.  In other words, the
variable will no longer be shared.

Furthermore, if the outer subroutine is anonymous and references a
lexical variable outside itself, then the outer and inner subroutines
will I<never> share the given variable.

This problem can usually be solved by making the inner subroutine
anonymous, using the C<sub {}> syntax.  When inner anonymous subs that
reference variables in outer subroutines are called or referenced, they
are automatically rebound to the current values of such variables.

=item Variable length lookbehind not implemented in regex;

marked by <-- HERE in m/%s/

(F) Lookbehind is allowed only for subexpressions whose length is fixed and
known at compile time. The <-- HERE shows in the regular expression about
where the problem was discovered. See L<perlre>.

=item Version number must be a constant number

(P) The attempt to translate a C<use Module n.n LIST> statement into
its equivalent C<BEGIN> block found an internal inconsistency with
the version number.

=item v-string in use/require is non-portable

(W portable) The use of v-strings is non-portable to older, pre-5.6, Perls.
If you want your scripts to be backward portable, use the floating
point version number: for example, instead of C<use 5.6.1> say
C<use 5.006_001>.  This of course won't help: the older Perls
won't suddenly start understanding newer features, but at least
they will show a sensible error message indicating the required
minimum version.

=item Warning: something's wrong

(W) You passed warn() an empty string (the equivalent of C<warn "">) or
you called it with no args and C<$_> was empty.

=item Warning: unable to close filehandle %s properly

(S) The implicit close() done by an open() got an error indication on
the close().  This usually indicates your file system ran out of disk
space.

=item Warning: Use of "%s" without parentheses is ambiguous

(S ambiguous) You wrote a unary operator followed by something that
looks like a binary operator that could also have been interpreted as a
term or unary operator.  For instance, if you know that the rand
function has a default argument of 1.0, and you write

    rand + 5;

you may THINK you wrote the same thing as

    rand() + 5;

but in actual fact, you got

    rand(+5);

So put in parentheses to say what you really mean.

=item Wide character in %s

(W utf8) Perl met a wide character (>255) when it wasn't expecting
one.  This warning is by default on for I/O (like print) but can be
turned off by C<no warnings 'utf8';>.  You are supposed to explicitly
mark the filehandle with an encoding, see L<open> and L<perlfunc/binmode>.

=item write() on closed filehandle %s

(W closed) The filehandle you're writing to got itself closed sometime
before now.  Check your control flow.

=item X outside of string

(F) You had a pack template that specified a relative position before
the beginning of the string being unpacked.  See L<perlfunc/pack>.

=item x outside of string

(F) You had a pack template that specified a relative position after
the end of the string being unpacked.  See L<perlfunc/pack>.

=item Xsub "%s" called in sort

(F) The use of an external subroutine as a sort comparison is not yet
supported.

=item Xsub called in sort

(F) The use of an external subroutine as a sort comparison is not yet
supported.

=item YOU HAVEN'T DISABLED SET-ID SCRIPTS IN THE KERNEL YET!

(F) And you probably never will, because you probably don't have the
sources to your kernel, and your vendor probably doesn't give a rip
about what you want.  Your best bet is to put a setuid C wrapper around
your script.

=item You need to quote "%s"

(W syntax) You assigned a bareword as a signal handler name.
Unfortunately, you already have a subroutine of that name declared,
which means that Perl 5 will try to call the subroutine when the
assignment is executed, which is probably not what you want.  (If it IS
what you want, put an & in front.)

=back

=cut