SYNOPSIS
use re 'taint';
($x) = ($^X =~ /^(.*)$/s); # $x is tainted here
$pat = '(?{ $foo = 1 })';
use re 'eval';
/foo${pat}bar/; # won't fail (when not under -T switch)
{
no re 'taint'; # the default
($x) = ($^X =~ /^(.*)$/s); # $x is not tainted here
no re 'eval'; # the default
/foo${pat}bar/; # disallowed (with or without -T switch)
}
use re 'debug'; # output debugging info during
/^(.*)$/s; # compile and run time
use re 'debugcolor'; # same as 'debug', but with colored output
...
use re qw(Debug All); # Finer tuned debugging options.
use re qw(Debug More);
no re qw(Debug ALL); # Turn of all re debugging in this scope
use re qw(is_regexp regexp_pattern); # import utility functions
my ($pat,$mods)=regexp_pattern(qr/foo/i);
if (is_regexp($obj)) {
print "Got regexp: ",
scalar regexp_pattern($obj); # just as perl would stringify it
} # but no hassle with blessed re's.
(We use $^X in these examples because it's tainted by default.)
DESCRIPTION
'taint' mode
When "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. This feature is useful when regex
operations on tainted data aren't meant to extract safe substrings, but
to perform other transformations.
'eval' mode
When "use re 'eval'" is in effect, a regex is allowed to contain "(?{
... })" zero-width assertions even if regular expression contains
variable interpolation. That is normally disallowed, since it is a
potential security risk. Note that this pragma is ignored when the
regular expression is obtained from tainted data, i.e. evaluation is
always disallowed with tainted regular expressions. See "(?{ code })"
in perlre.
that obtained by running a "-DDEBUGGING"-enabled perl interpreter with
the -Dr switch. It may be quite voluminous depending on the complexity
of the match. Using "debugcolor" instead of "debug" enables a form of
output that can be used to get a colorful display on terminals that
understand termcap color sequences. Set $ENV{PERL_RE_TC} to a comma-
separated list of "termcap" properties to use for highlighting strings
on/off, pre-point part on/off. See "Debugging regular expressions" in
perldebug for additional info.
As of 5.9.5 the directive "use re 'debug'" and its equivalents are
lexically scoped, as the other directives are. However they have both
compile-time and run-time effects.
See "Pragmatic Modules" in perlmodlib.
'Debug' mode
Similarly "use re 'Debug'" produces debugging output, the difference
being that it allows the fine tuning of what debugging output will be
emitted. Options are divided into three groups, those related to
compilation, those related to execution and those related to special
purposes. The options are as follows:
Compile related options
COMPILE
Turns on all compile related debug options.
PARSE
Turns on debug output related to the process of parsing the
pattern.
OPTIMISE
Enables output related to the optimisation phase of
compilation.
TRIEC
Detailed info about trie compilation.
DUMP
Dump the final program out after it is compiled and optimised.
Execute related options
EXECUTE
Turns on all execute related debug options.
MATCH
Turns on debugging of the main matching loop.
TRIEE
Extra debugging of how tries execute.
INTUIT
Enable debugging of start point optimisations.
Extra debugging options
STACK
Enable debugging of the recursion stack in the engine. Enabling
or disabling this option automatically does the same for
debugging states as well. This output from this can be quite
large.
OPTIMISEM
Enable enhanced optimisation debugging and start point
optimisations. Probably not useful except when debugging the
regex engine itself.
OFFSETS
Dump offset information. This can be used to see how regops
correlate to the pattern. Output format is
NODENUM:POSITION[LENGTH]
Where 1 is the position of the first char in the string. Note
that position can be 0, or larger than the actual length of the
pattern, likewise length can be zero.
OFFSETSDBG
Enable debugging of offsets information. This emits copious
amounts of trace information and doesn't mesh well with other
debug options.
Almost definitely only useful to people hacking on the offsets
part of the debug engine.
Other useful flags
These are useful shortcuts to save on the typing.
ALL Enable all options at once except OFFSETS, OFFSETSDBG and
BUFFERS
All Enable DUMP and all execute options. Equivalent to:
use re 'debug';
MORE
More
Enable TRIEM and all execute compile and execute options.
As of 5.9.5 the directive "use re 'debug'" and its equivalents are
lexically scoped, as the other directives are. However they have both
compile-time and run-time effects.
Exportable Functions
As of perl 5.9.5 're' debug contains a number of utility functions that
may be optionally exported into the caller's namespace. They are listed
below.
is_regexp($ref)
containing the pattern and the second containing the modifiers used
when the pattern was compiled.
my ($pat, $mods) = regexp_pattern($ref);
In scalar context it returns the same as perl would when
strigifying a raw "qr//" with the same pattern inside. If the
argument is not a compiled reference then this routine returns
false but defined in scalar context, and the empty list in list
context. Thus the following
if (regexp_pattern($ref) eq '(?i-xsm:foo)')
will be warning free regardless of what $ref actually is.
Like "is_regexp" this function will not be confused by overloading
or blessing of the object.
regmust($ref)
If the argument is a compiled regular expression as returned by
"qr//", then this function returns what the optimiser consiers to
be the longest anchored fixed string and longest floating fixed
string in the pattern.
A fixed string is defined as being a substring that must appear for
the pattern to match. An anchored fixed string is a fixed string
that must appear at a particular offset from the beginning of the
match. A floating fixed string is defined as a fixed string that
can appear at any point in a range of positions relative to the
start of the match. For example,
my $qr = qr/here .* there/x;
my ($anchored, $floating) = regmust($qr);
print "anchored:'$anchored'\nfloating:'$floating'\n";
results in
anchored:'here'
floating:'there'
Because the "here" is before the ".*" in the pattern, its position
can be determined exactly. That's not true, however, for the
"there"; it could appear at any point after where the anchored
string appeared. Perl uses both for its optimisations, prefering
the longer, or, if they are equal, the floating.
NOTE: This may not necessarily be the definitive longest anchored
and floating string. This will be what the optimiser of the Perl
that you are using thinks is the longest. If you believe that the
result is wrong please report it via the perlbug utility.
regname($name,$all)
Returns the contents of a named buffer of the last successful
match. If $all is true, then returns an array ref containing one
Note: this result is always the actual number of distinct named
buffers defined, it may not actually match that which is returned
by "regnames()" and related routines when those routines have not
been called with the $all parameter set.
SEE ALSO
"Pragmatic Modules" in perlmodlib.
|
