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Anything that has been discontinued, deprecated, or fixed as a bug from perl4.
- * Discontinuance
-
Symbols starting with "_" are no longer forced into package main, except for $_
itself (and @_, etc.).
package test;
$_legacy = 1;
package main;
print "\$_legacy is ",$_legacy,"\n";
# perl4 prints: $_legacy is 1
# perl5 prints: $_legacy is
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- * Deprecation
-
Double-colon is now a valid package separator in a variable name. Thus these behave
differently in perl4 vs. perl5, because the packages don't exist.
$a=1;$b=2;$c=3;$var=4;
print "$a::$b::$c ";
print "$var::abc::xyz\n";
# perl4 prints: 1::2::3 4::abc::xyz
# perl5 prints: 3
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Given that :: is now the preferred package delimiter, it is debatable
whether this should be classed as a bug or not. (The older package delimiter, ' ,is used
here)
$x = 10 ;
print "x=${'x}\n" ;
# perl4 prints: x=10
# perl5 prints: Can't find string terminator "'" anywhere before EOF
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You can avoid this problem, and remain compatible with perl4, if you always explicitly
include the package name:
$x = 10 ;
print "x=${main'x}\n" ;
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Also see precedence traps, for parsing $:.
- * BugFix
-
The second and third arguments of splice() are now evaluated in scalar
context (as the Camel says) rather than list context.
sub sub1{return(0,2) } # return a 2-element list
sub sub2{ return(1,2,3)} # return a 3-element list
@a1 = ("a","b","c","d","e");
@a2 = splice(@a1,&sub1,&sub2);
print join(' ',@a2),"\n";
# perl4 prints: a b
# perl5 prints: c d e
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- * Discontinuance
-
You can't do a goto into a block that is optimized away. Darn.
goto marker1;
for(1){
marker1:
print "Here I is!\n";
}
# perl4 prints: Here I is!
# perl5 errors: Can't "goto" into the middle of a foreach loop
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|
- * Discontinuance
-
It is no longer syntactically legal to use whitespace as the name of a variable, or as a
delimiter for any kind of quote construct. Double darn.
$a = ("foo bar");
$b = q baz ;
print "a is $a, b is $b\n";
# perl4 prints: a is foo bar, b is baz
# perl5 errors: Bareword found where operator expected
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|
- * Discontinuance
-
The archaic while/if BLOCK BLOCK syntax is no longer supported.
if { 1 } {
print "True!";
}
else {
print "False!";
}
# perl4 prints: True!
# perl5 errors: syntax error at test.pl line 1, near "if {"
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|
- * BugFix
-
The ** operator now binds more tightly than unary minus. It was documented
to work this way before, but didn't.
print -4**2,"\n";
# perl4 prints: 16
# perl5 prints: -16
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|
- * Discontinuance
-
The meaning of foreach{} has changed slightly when it is iterating over a
list which is not an array. This used to assign the list to a temporary array, but no longer
does so (for efficiency). This means that you'll now be iterating over the actual values,
not over copies of the values. Modifications to the loop variable can change the original
values.
@list = ('ab','abc','bcd','def');
foreach $var (grep(/ab/,@list)){
$var = 1;
}
print (join(':',@list));
# perl4 prints: ab:abc:bcd:def
# perl5 prints: 1:1:bcd:def
|
|
To retain Perl4 semantics you need to assign your list explicitly to a temporary array
and then iterate over that. For example, you might need to change
foreach $var (grep(/ab/,@list)){
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|
to
foreach $var (@tmp = grep(/ab/,@list)){
|
|
Otherwise changing $var will clobber the values of @list. (This most often happens when
you use $_ for the loop variable, and call subroutines in the loop that don't
properly localize $_.)
- * Discontinuance
-
split with no arguments now behaves like split ' ' (which
doesn't return an initial null field if $_ starts with whitespace), it used to behave like split
/\s+/ (which does).
$_ = ' hi mom';
print join(':', split);
# perl4 prints: :hi:mom
# perl5 prints: hi:mom
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|
- * BugFix
-
Perl 4 would ignore any text which was attached to an -e switch, always taking the
code snippet from the following arg. Additionally, it would silently accept an -e
switch without a following arg. Both of these behaviors have been fixed.
perl -e'print "attached to -e"' 'print "separate arg"'
# perl4 prints: separate arg
# perl5 prints: attached to -e
perl -e
# perl4 prints:
# perl5 dies: No code specified for -e.
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|
- * Discontinuance
-
In Perl 4 the return value of push was undocumented, but it was actually the
last value being pushed onto the target list. In Perl 5 the return value of push
is documented, but has changed, it is the number of elements in the resulting list.
@x = ('existing');
print push(@x, 'first new', 'second new');
# perl4 prints: second new
# perl5 prints: 3
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|
- * Deprecation
- Some error messages will be different.
- * Discontinuance
- In Perl 4, if in list context the delimiters to the first argument of
split()
were ??, the result would be placed in @_ as well as being
returned. Perl 5 has more respect for your subroutine arguments.
- * Discontinuance
- Some bugs may have been inadvertently removed. :-)
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