allow eval-groups in patterns only if they C<use re 'eval';>

[p5sagit/p5-mst-13.2.git] / lib / re.pm

diff --git a/lib/re.pm b/lib/re.pm
index ff38c41..b7375e3 100644 (file)
--- a/lib/re.pm
+++ b/lib/re.pm
@@ -6,26 +6,42 @@ re - Perl pragma to alter regular expression behaviour
 
 =head1 SYNOPSIS
 
-    ($x) = ($^X =~ /^(.*)$/s);     # $x is not tainted here
+    use re 'taint';
+    ($x) = ($^X =~ /^(.*)$/s);     # $x is tainted here
 
-    use re "taint";
-    ($x) = ($^X =~ /^(.*)$/s);     # $x _is_ tainted here
+    use re 'eval';
+    /foo(?{ $foo = 1 })bar/;      # won't fail (when not under -T switch)
+
+    {
+       no re 'taint';             # the default
+       ($x) = ($^X =~ /^(.*)$/s); # $x is not tainted here
+
+       no re 'eval';              # the default
+       /foo(?{ $foo = 1 })bar/;   # disallowed (with or without -T switch)
+    }
 
 =head1 DESCRIPTION
 
 When C<use re 'taint'> is in effect, and a tainted string is the target
 of a regex, the regex memories (or values returned by the m// operator
-in list context) are tainted.
+in list context) are tainted.  This feature is useful when regex operations
+on tainted data aren't meant to extract safe substrings, but to perform
+other transformations.
 
-This feature is useful when regex operations on tainted data aren't
-meant to extract safe substrings, but to perform other transformations.
+When C<use re 'eval'> is in effect, a regex is allowed to contain
+C<(?{ ... })> zero-width assertions (which may not be interpolated in
+the regex).  That is normally disallowed, since it is a potential security
+risk.  Note that this pragma is ignored when perl detects tainted data,
+i.e.  evaluation is always disallowed with tainted data.  See
+L<perlre/(?{ code })>.
 
 See L<perlmodlib/Pragmatic Modules>.
 
 =cut
 
 my %bitmask = (
-taint => 0x00100000
+taint  => 0x00100000,
+eval   => 0x00200000,
 );
 
 sub bits {