printf() and sprintf() previously reset the numeric locale back to the default "C" locale. This has been fixed.
Numbers formatted according to the local numeric locale (such as using a decimal comma instead of a decimal dot) caused "isn't numeric" warnings, even while the operations accessing those numbers produced correct results. These warnings have been discontinued.
Memory leaks
The eval 'return sub {...}' construct could sometimes leak memory. This has been fixed.
Operations that aren't filehandle constructors used to leak memory when used on invalid filehandles. This has been fixed.
Constructs that modified @_ could fail to deallocate values in @_ and thus leak memory. This has been corrected.
Spurious subroutine stubs after failed subroutine calls
Perl could sometimes create empty subroutine stubs when a subroutine was not found in the package. Such cases stopped later method lookups from progressing into base packages. This has been corrected.
Taint failures under -U
When running in unsafe mode, taint violations could sometimes cause silent failures. This has been fixed.
END blocks and the -c switch
Prior versions used to run BEGIN and END blocks when Perl was run in compile-only mode. Since this is typically not the expected behavior, END blocks are not executed anymore when the -c switch is used.
See CHECK blocks for how to run things when the compile phase ends.
Potential to leak DATA filehandles
Using the __DATA__ token creates an implicit filehandle to the file that contains the token. It is the program's responsibility to close it when it is done reading from it.
This caveat is now better explained in the documentation. See perldata.
New or Changed Diagnostics
"%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.
"my sub" not yet implemented
(F) Lexically scoped subroutines are not yet implemented. Don't try that yet.
"our" variable %s redeclared
(W misc) You seem to have already declared the same global once before in the current lexical scope.
'!' allowed only after types %s
(F) The '!' is allowed in pack() and unpack() only after certain types. See perlfunc/pack.
/ 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 perlfunc/pack.
/ 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 perlfunc/pack.
/ 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 perlfunc/pack.
/ must follow a numeric type
(F)
