Opcode - Disable named opcodes when compiling perl code
use Opcode;Perl code is always compiled into an internal format before execution.
Evaluating perl code (e.g. via "eval" or "do 'file'") causes the code to be compiled into an internal format and then, provided there was no error in the compilation, executed. The internal format is based on many distinct opcodes.
By default no opmask is in effect and any code can be compiled.
The Opcode module allow you to define an operator mask to be in effect when perl next compiles any code. Attempting to compile code which contains a masked opcode will cause the compilation to fail with an error. The code will not be executed.
The Opcode module is not usually used directly. See the ops pragma and Safe modules for more typical uses.
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Your mileage will vary. If in any doubt do not use it.
The canonical list of operator names is the contents of the array PL_op_name defined and initialised in file opcode.h of the Perl source distribution (and installed into the perl library).
Each operator has both a terse name (its opname) and a more verbose or recognisable descriptive name. The opdesc function can be used to return a list of descriptions for a list of operators.
Many of the functions and methods listed below take a list of operators as parameters. Most operator lists can be made up of several types of element. Each element can be one of
Operator names are typically small lowercase words like enterloop, leaveloop, last, next, redo etc. Sometimes they are rather cryptic like gv2cv, i_ncmp and ftsvtx.
Operator tags can be used to refer to groups (or sets) of operators. Tag names always begin with a colon. The Opcode module defines several optags and the user can define others using the define_optag function.
An opname or optag can be prefixed with an exclamation mark, e.g., !mkdir. Negating an opname or optag means remove the corresponding ops from the accumulated set of ops at that point.
An opset as a binary string of approximately 44 bytes which holds a set or zero or more operators.
The opset and opset_to_ops functions can be used to convert from a list of operators to an opset and vice versa.
Wherever a list of operators can be given you can use one or more opsets. See also Manipulating Opsets below.
The Opcode package contains functions for manipulating operator names tags and sets. All are available for export by the package.
In a scalar context opcodes returns the number of opcodes in this version of perl (around 350 for perl-5.7.0).
In a list context it returns a list of all the operator names. (Not yet implemented, use @names = opset_to_ops(full_opset).)
Returns an opset containing the listed operators.
Returns a list of operator names corresponding to those operators in the set.
Returns a string representation of an opset. Can be handy for debugging.
Returns an opset which includes all operators.
Returns an opset which contains no operators.
Returns an opset which is the inverse set of the one supplied.
Returns true if the supplied opset looks like a valid opset (is the right length etc) otherwise it returns false. If an optional second parameter is true then verify_opset will croak on an invalid opset instead of returning false.
Most of the other Opcode functions call verify_opset automatically and will croak if given an invalid opset.
Define OPTAG as a symbolic name for OPSET. Optag names always start with a colon :.
The optag name used must not be defined already (define_optag will croak if it is already defined). Optag names are global to the perl process and optag definitions cannot be altered or deleted once defined.
It is strongly recommended that applications using Opcode should use a leading capital letter on their tag names since lowercase names are reserved for use by the Opcode module. If using Opcode within a module you should prefix your tags names with the name of your module to ensure uniqueness and thus avoid clashes with other modules.
Adds the supplied opset to the current opmask. Note that there is currently no mechanism for unmasking ops once they have been masked. This is intentional.
Returns an opset corresponding to the current opmask.
This takes a list of operator names and returns the corresponding list of operator descriptions.
Dumps to STDOUT a two column list of op names and op descriptions. If an optional pattern is given then only lines which match the (case insensitive) pattern will be output.
It's designed to be used as a handy command line utility:
perl -MOpcode=opdump -e opdump
perl -MOpcode=opdump -e 'opdump Eval'Opsets may be manipulated using the perl bit vector operators & (and), | (or), ^ (xor) and ~ (negate/invert).
However you should never rely on the numerical position of any opcode within the opset. In other words both sides of a bit vector operator should be opsets returned from Opcode functions.
Also, since the number of opcodes in your current version of perl might not be an exact multiple of eight, there may be unused bits in the last byte of an upset. This should not cause any problems (Opcode functions ignore those extra bits) but it does mean that using the ~ operator will typically not produce the same 'physical' opset 'string' as the invert_opset function.
$bool = opset_eq($opset1, $opset2) true if opsets are logically
equivalent
$yes = opset_can($opset, @ops) true if $opset has all @ops set
@diff = opset_diff($opset1, $opset2) => ('foo', '!bar', ...) null stub scalar pushmark wantarray const defined undef
rv2sv sassign
rv2av aassign aelem aelemfast aelemfast_lex aslice kvaslice
av2arylen
rv2hv helem hslice kvhslice each values keys exists delete
aeach akeys avalues reach rvalues rkeys
preinc i_preinc predec i_predec postinc i_postinc
postdec i_postdec int hex oct abs pow multiply i_multiply
divide i_divide modulo i_modulo add i_add subtract i_subtract
left_shift right_shift bit_and bit_xor bit_or negate i_negate
not complement
lt i_lt gt i_gt le i_le ge i_ge eq i_eq ne i_ne ncmp i_ncmp
slt sgt sle sge seq sne scmp
substr vec stringify study pos length index rindex ord chr
ucfirst lcfirst uc lc fc quotemeta trans transr chop schop
chomp schomp
match split qr
list lslice splice push pop shift unshift reverse
cond_expr flip flop andassign orassign dorassign and or dor xor
warn die lineseq nextstate scope enter leave
rv2cv anoncode prototype coreargs
entersub leavesub leavesublv return method method_named
-- XXX loops via recursion?
leaveeval -- needed for Safe to operate, is safe
without enterevalThese memory related ops are not included in :base_core because they can easily be used to implement a resource attack (e.g., consume all available memory).
concat repeat join range
anonlist anonhashNote that despite the existence of this optag a memory resource attack may still be possible using only :base_core ops.
Disabling these ops is a very heavy handed way to attempt to prevent a memory resource attack. It's probable that a specific memory limit mechanism will be added to perl in the near future.
These loop ops are not included in :base_core because they can easily be used to implement a resource attack (e.g., consume all available CPU time).
grepstart grepwhile
mapstart mapwhile
enteriter iter
enterloop leaveloop unstack
last next redo
gotoThese ops enable filehandle (rather than filename) based input and output. These are safe on the assumption that only pre-existing filehandles are available for use. Usually, to create new filehandles other ops such as open would need to be enabled, if you don't take into account the magical open of ARGV.
readline rcatline getc read
formline enterwrite leavewrite
print say sysread syswrite send recv
eof tell seek sysseek
readdir telldir seekdir rewinddir