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Re^3: Is it safe to use external strings for regexes? (Keyword::Simple)

by LanX (Sage)
on Oct 06, 2021 at 17:06 UTC ( #11137270=note: print w/replies, xml ) Need Help??

in reply to Re^2: Is it safe to use external strings for regexes? (use Safe)
in thread Is it safe to use external strings for regexes?

It's indeed possible to bend the parser in a way that it thinks BEGIN and family are subs

use strict; use warnings; use Keyword::Simple; sub no_begin ($&){ warn "no_begin(@_) called"; } my @code; BEGIN{ my @compile_blocks = qw(BEGIN UNITCHECK CHECK INIT END); for my $block (@compile_blocks) { # bend parser Keyword::Simple::define $block, sub { my ($ref) = @_; substr($$ref, 0, 0) = "no_begin '$block', sub"; }; # test code push @code , <<__CODE__; $block { die "owened by $block" } __CODE__ } } BEGIN { die "owened by BEGIN" }; UNITCHECK { die "owened by UNITCHECK" }; CHECK { die "owened by CHECK" }; INIT { die "owened by INIT" }; END { die "owened by END" }; eval join "\n", @code;

-*- mode: compilation; default-directory: "d:/tmp/pm/" -*- Compilation started at Wed Oct 6 19:04:01 C:/Strawberry/perl/bin\perl.exe -w d:/tmp/pm/ no_begin(BEGIN CODE(0x694268)) called at d:/tmp/pm/KW_simple_regex_BEG line 6. no_begin(UNITCHECK CODE(0x6556d0)) called at d:/tmp/pm/KW_simple_regex line 6. no_begin(CHECK CODE(0x6942b0)) called at d:/tmp/pm/KW_simple_regex_BEG line 6. no_begin(INIT CODE(0x6c8aa0)) called at d:/tmp/pm/KW_simple_regex_BEGI line 6. no_begin(END CODE(0x6c8c38)) called at d:/tmp/pm/KW_simple_regex_BEGIN line 6. Bareword found where operator expected at (eval 5) line 5, near "} CHECK" (Missing operator before CHECK?)

But unfortunately does evaling the code not catch parsing errors anymore... (reason here BEGIN{} blocks don't need a trailing semicolon)

so the answer is:

  • Yes BEGIN* blocks can be disabled.
  • But this is best done in an extra process

Cheers Rolf
(addicted to the Perl Programming Language :)
Wikisyntax for the Monastery

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