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With $/ set to undef, "slurping" an empty file returns
a string of zero length (instead of undef, as it used to) the first time the
HANDLE is read after $/ is set to undef. Further reads yield undef.
This means that the following will append "foo" to an empty file (it used to do
nothing):
perl -0777 -pi -e 's/^/foo/' empty_file
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The behaviour of:
perl -pi -e 's/^/foo/' empty_file
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is unchanged (it continues to leave the file empty).
Line numbers (as reflected by caller() and most diagnostics) within eval '...'
were often incorrect where here documents were involved. This has been corrected.
Lexical lookups for variables appearing in eval '...' within functions that
were themselves called within an eval '...' were searching the wrong place for
lexicals. The lexical search now correctly ends at the subroutine's block boundary.
The use of return within eval {...} caused $@ not to be reset
correctly when no exception occurred within the eval. This has been fixed.
Parsing of here documents used to be flawed when they appeared as the replacement
expression in eval 's/.../.../e'. This has been fixed.
Some "errors" encountered at compile time were by necessity generated as warnings
followed by eventual termination of the program. This enabled more such errors to be reported
in a single run, rather than causing a hard stop at the first error that was encountered.
The mechanism for reporting such errors has been reimplemented to queue compile-time errors
and report them at the end of the compilation as true errors rather than as warnings. This
fixes cases where error messages leaked through in the form of warnings when code was compiled
at run time using eval STRING, and also allows such errors to be reliably trapped
using eval "...".
Sometimes implicitly closed filehandles (as when they are localized, and Perl automatically
closes them on exiting the scope) could inadvertently set $? or $!. This has been corrected.
When taking a slice of a literal list (as opposed to a slice of an array or hash), Perl
used to return an empty list if the result happened to be composed of all undef values.
The new behavior is to produce an empty list if (and only if) the original list was empty.
Consider the following example:
@a = (1,undef,undef,2)[2,1,2];
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The old behavior would have resulted in @a having no elements. The new behavior ensures it
has three undefined elements.
Note in particular that the behavior of slices of the following cases remains unchanged:
@a = ()[1,2];
@a = (getpwent)[7,0];
@a = (anything_returning_empty_list())[2,1,2];
@a = @b[2,1,2];
@a = @c{'a','b','c'};
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See perldata.
A scalar reference prototype now correctly allows a hash or array element in that slot.
The goto &sub construct works correctly when &sub happens
to be autoloaded.
The autoquoting of barewords preceded by - did not work in prior versions when
the integer pragma was enabled. This has been fixed.
When code in a destructor threw an exception, it went unnoticed in earlier versions of Perl,
unless someone happened to be looking in $@ just after the point the destructor happened to
run. Such failures are now visible as warnings when warnings are enabled.
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.
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.
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.
When running in unsafe mode, taint violations could sometimes cause silent failures. This
has been fixed.
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, or if compilation fails.
See /"Support for CHECK blocks" for how
to run things when the compile phase ends.
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.
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