|
All types of RE traps.
- * Regular Expression
-
s'$lhs'$rhs' now does no interpolation on either side. It used to
interpolate $lhs but not $rhs. (And still does not match a literal '$' in string)
$a=1;$b=2;
$string = '1 2 $a $b';
$string =~ s'$a'$b';
print $string,"\n";
# perl4 prints: $b 2 $a $b
# perl5 prints: 1 2 $a $b
|
|
- * Regular Expression
-
m//g now attaches its state to the searched string rather than the regular
expression. (Once the scope of a block is left for the sub, the state of the searched string
is lost)
$_ = "ababab";
while(m/ab/g){
&doit("blah");
}
sub doit{local($_) = shift; print "Got $_ "}
# perl4 prints: Got blah Got blah Got blah Got blah
# perl5 prints: infinite loop blah...
|
|
- * Regular Expression
-
Currently, if you use the m//o qualifier on a regular expression within an
anonymous sub, all closures generated from that anonymous sub will use the regular
expression as it was compiled when it was used the very first time in any such closure. For
instance, if you say
sub build_match {
my($left,$right) = @_;
return sub { $_[0] =~ /$left stuff $right/o; };
}
$good = build_match('foo','bar');
$bad = build_match('baz','blarch');
print $good->('foo stuff bar') ? "ok\n" : "not ok\n";
print $bad->('baz stuff blarch') ? "ok\n" : "not ok\n";
print $bad->('foo stuff bar') ? "not ok\n" : "ok\n";
|
|
For most builds of Perl5, this will print: ok not ok not ok
build_match() will always return a sub which matches the contents of $left and $right as
they were the first time that build_match() was called, not as they are in the
current call.
- * Regular Expression
-
If no parentheses are used in a match, Perl4 sets $+ to the whole match,
just like $&. Perl5 does not.
"abcdef" =~ /b.*e/;
print "\$+ = $+\n";
# perl4 prints: bcde
# perl5 prints:
|
|
- * Regular Expression
-
substitution now returns the null string if it fails
$string = "test";
$value = ($string =~ s/foo//);
print $value, "\n";
# perl4 prints: 0
# perl5 prints:
|
|
Also see Numerical Traps for another example of this new
feature.
- * Regular Expression
-
s`lhs`rhs` (using backticks) is now a normal substitution, with no backtick
expansion
$string = "";
$string =~ s`^`hostname`;
print $string, "\n";
# perl4 prints: <the local hostname>
# perl5 prints: hostname
|
|
- * Regular Expression
-
Stricter parsing of variables used in regular expressions
s/^([^$grpc]*$grpc[$opt$plus$rep]?)//o;
# perl4: compiles w/o error
# perl5: with Scalar found where operator expected ..., near "$opt$plus"
|
|
an added component of this example, apparently from the same script, is the actual value
of the s'd string after the substitution. [$opt] is a character class in perl4
and an array subscript in perl5
$grpc = 'a';
$opt = 'r';
$_ = 'bar';
s/^([^$grpc]*$grpc[$opt]?)/foo/;
print ;
# perl4 prints: foo
# perl5 prints: foobar
|
|
- * Regular Expression
-
Under perl5, m?x? matches only once, like ?x?. Under perl4, it
matched repeatedly, like /x/ or m!x!.
$test = "once";
sub match { $test =~ m?once?; }
&match();
if( &match() ) {
# m?x? matches more then once
print "perl4\n";
} else {
# m?x? matches only once
print "perl5\n";
}
# perl4 prints: perl4
# perl5 prints: perl5
|
|
|
|
