How to interpret a string as perl code and execute it?

[sg]

Hello,

If a perl script gets access to a string, how can the script interpret the contents of the string as perl code and execute it? My naive attempt failed:

use diagnostics;
use warnings;
use strict;

my $a_code =<<'CODE';

sub tryme
{
   my $foo = shift;
   return $foo + 2;
}

CODE

# Intent shown here does _not_ work
my $ans = eval{ $a_code; tryme( 3 ); } or die "doesn't work";

The error might be in the way in which the code in being packaged into the string $a_code, or in how $a_code is being used, or in both.

[Corion]

You want "string-eval", not "block-eval":

my $ans = eval "$acode; tryme(3)";
if (my $err = $@) {
    die "Caught error: $err in code [$acode]";
};

[sg]

Thanks; string eval does work in the example. But the following bit more complex example, in which the string needs to use the "context" of the executing script, fails:

use diagnostics;
use warnings;
use strict;

my %h;
$h{ 'a' }{ 'b' } = 5;

my $b_code =<<'CODE';

sub tryme_b
{
   my $foo = shift;
   return ${ $foo }{ 'a' }{ 'b' };
}

CODE

my $ans = eval "$b_code; tryme_b( \%h );" or die "[$b_code] doesn't wo
+rk:$@";

print "b:$ans,\n";

[Corion]

Would your code work when run stand-alone? Have you printed out the code you're trying to eval? Have you looked at the error message and looked at what causes it?

The following change to your code might help you see the problem:

use diagnostics;
use warnings;
use strict;
use Data::Dumper;

my %h;
$h{ 'a' }{ 'b' } = 5;

my $b_code =<<'CODE';

sub tryme_b
{
   my $foo = shift;
   return ${ $foo }{ 'a' }{ 'b' };
}

CODE

my $c = "$b_code; tryme_b( \%h );";
my $ans = eval $c or die "[$c] doesn't work:$@";

print "b:$ans,\n";

Also, basic debugging in your tryme_b would also show you what goes wrong.

[ikegami]

You didn't properly convert your Perl to code a Perl string literal. To generate the string

tryme_b( \%h )

you need the string literal

"tryme_b( \\%h )"