How to do a "perl -c(w)" check instead of an "eval $string" on a code string

Your Mother has asked for the wisdom of the Perl Monks concerning the following question:

I am taking raw Perl in a form (maybe, I might go back to file based code in this case but I'm interested in exploring it this way first). I want do the equivalent of `perl -c` on it because I want to see it's valid without evaling it; which might pollute namespaces or cause other problems. I'm at a bit of a loss where to go with this. In pseudo-code-

my $snippet = $c->request->param("filter");
my $package = __PACKAGE__ . "::" . get_uuid_name();
my $code = "package $package; use strict; use warnings;";
$code .= $snippet;
$code .= ";\n1;";
# ... ?
my $perl = qx/ which perl /;
my $result = qx/ perl -c $code /; # CAN this work? If so, how? I'm a s
+hell-tard.
[download]

Or can I "safely" eval it and remove it from the @INC by something like delete $INC{$generated_package_name}? I might like to do that so I could deparse or plumb the namespace anyway...?

I realize this is a bit of a fuzzy SOPW but I'm just exploring so looking for any bones, table scraps, or clues.

I'm also thinking of forcing it into a sub so the wrapper puts the user supplied code into "package ...; sub run { my ( $vars, $you, $get ) = @_; YOUR CODE HERE }" etc. I think is safer/easier but I want to allow the user to initialize things in the package for efficiency, sub-classing, whatnot.

Comment on How to do a "perl -c(w)" check instead of an "eval $string" on a code string Select or Download Code

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Re: How to do a "perl -c(w)" check instead of an "eval $string" on a code string by jdporter (Paladin) on Jan 20, 2009 at 03:41 UTC
Well, you can set `$^C` at runtime (or rather, at BEGIN time): `eval 'BEGIN { $^C = 1 } ' . $code; # where $code contains what you wan +t to test` [download] then test `$@` for any compile error messages. Of course, eval has problems, as you've already discussed; so to deal with that, you could use Safe: `use Safe; my $compartment = new Safe; $compartment->reval( 'no warnings; BEGIN { $^C = 1 } ' . $code );` [download] Tested. :-) Between the mind which plans and the hands which build, there must be a mediator... and this mediator must be the heart.	[reply] [d/l] [select]
Re^2: How to do a "perl -c(w)" check instead of an "eval $string" on a code string by Your Mother (Archbishop) on Jan 20, 2009 at 05:54 UTC
That's hawt++.	[reply]
Re: How to do a "perl -c(w)" check instead of an "eval $string" on a code string by shmem (Chancellor) on Jan 20, 2009 at 00:18 UTC
`$code .= ";\n1;"; # ... ? my $perl = qx/ which perl /; my $result = qx/ perl -c $code /; # CAN this work? If so, how? I'm a s +hell-tard.` [download] Yes, it can. The `my $perl = qx/ which perl /` is somewhat pointless, since your are already running perl, so how you've invoked it is in `$^X`. `my $result = qx/perl -c -e '$code' 2>&1/; # bundle STDOUT and STDERR` [download] should give you either `-e syntax OK` [download] or any error which you can then examine. For simple snippets without quotes, that is! Otherwise you'd grab File::Temp, write a tempfile and examine `my $result = qx/perl -c $tempfile 2>&1/;` [download] update: WRT evaling - you could switch to some other package before the eval `package My::Eval::Evil; eval $code; if ($@) { .... } package main; # or whatever package you've been in` [download] and then throw away the symbol tables for `My::Eval::Evil` and the eval'ed code's package. That reduces the risk of name space pollution a bit. But the eval'ed code could still reach into your package (via examining %INC or writing into main::), so the safest (for some value of safety) is writing a tempfile and shell out a brand new perl. `perl -e 'sub foo {print "foo\n" } package Foo; my $code = "main::foo += sub {print \"bar\\n\" }"; eval $code; package main; foo()' bar` [download]	[reply] [d/l] [select]
Re^2: How to do a "perl -c(w)" check instead of an "eval $string" on a code string by Your Mother (Archbishop) on Jan 20, 2009 at 00:57 UTC
Also nice and good tips. I don't know why I didn't consider tempfiles already. I use them all the time and I've got a uuid already so it can go in the app's files. Sigh.	[reply]
Re^3: How to do a "perl -c(w)" check instead of an "eval $string" on a code string by shmem (Chancellor) on Jan 20, 2009 at 01:12 UTC
If you're interested in success/failure only, you could run `system LIST` and check the exit code. That would fix the quoting issue of `-e`: `system $^X, '-wce', $code and warn "syntax check failed\n";` [download]	[reply] [d/l] [select]
Re: How to do a "perl -c(w)" check instead of an "eval $string" on a code string by doom (Deacon) on Jan 20, 2009 at 00:14 UTC
You're on the right track, but you need to know about the -e command line switch (try reading man perlrun). So you'll do something like this: `my $result = qx/ perl -cw -e '$code' 2>&1/;` [download] Where you'll then need to scrape the $result string to find out if it passed or failed. There's another angle to the problem though, you'll need to run the $code through some sort of shell quoting routine, to make sure you don't confuse the shell with characters in perl that also happen to be significant to the shell. I think the cpan module String::ShellQuote works okay for this. (Note: updated, stealing a hint from shmem to append 2>&1 to the command, this makes sure you'll capture error messages to $result.)	[reply] [d/l]
Re^2: How to do a "perl -c(w)" check instead of an "eval $string" on a code string by Your Mother (Archbishop) on Jan 20, 2009 at 00:55 UTC
Nice. I know `-e`, I figured it was out because of shell quoting but you've put me on the right track to at least play with that. Of course now that I write that I realize I could just open a pipe to perl...	[reply] [d/l]
Re: How to do a "perl -c(w)" check instead of an "eval $string" on a code string by merlyn (Sage) on Jan 20, 2009 at 00:26 UTC
Or can I "safely" eval it Beware that even "perl -c" will run "BEGIN" and "use" items, by design. -- Randal L. Schwartz, Perl hacker	[reply]
Re^2: How to do a "perl -c(w)" check instead of an "eval $string" on a code string by Your Mother (Archbishop) on Jan 20, 2009 at 01:01 UTC
Yeppers. I was thinking about `use` but I tend to forget about BEGIN; and INIT and CHECK for that matter. And I discover this minute that there is a UNITCHECK at all... Time to do some (re)reading.	[reply] [d/l]