Selective string interpolation

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

Fellow Monks,

I recently read through Jeffery Goff's excellent Parse::RecDescent tutorial. This inspired me to write my own context free grammar to parse the results of Data::Dumper, as eval-ing the structure is a huge security hole.

I've got everything working except for escaped character interpolation on double-quoted strings (e.g. "\t", "\n"). In other words, I want to be able to convert the string '\t' into ASCII 9. Is there an easy way to do this other than writing regexs for every escape I want to catch? Please note that I do not want to use eval, as this would just reintroduce the security hole. I also do not want to do any kind of variable expansion.

Thanks!

-Ton

BTW: I realize that Data::Dumper dumps its strings in single quote mode. The interpolation is solely for completeness. :)

-----
Be bloody, bold, and resolute; laugh to scorn
The power of man...

Comment on Selective string interpolation

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Re: Selective string interpolation by japhy (Canon) on Jun 29, 2001 at 03:48 UTC
You could try something like: `$string =~ s/(?<!\\)((?:\\\\)*)([\$\@])/$1\\$2/g; $string = eval qq{ << "I KNOW THIS STRING IS NOT IN THERE" $string I KNOW THIS STRING IS NOT IN THERE };` [download] `japhy` -- Perl and Regex Hacker	[reply] [d/l]
Re: Selective string interpolation by tadman (Prior) on Jun 29, 2001 at 03:46 UTC
This is a bit tricky because there are a variety of escape types to handle. In particular, there are the "regular" codes like '\n' which translate into a single character, but there are also others. '\cX' is the equivalent of CTRL-X, where X is a letter from a to z, or also a few others in the nearby ASCII space (such as ESC). '\xNN' is the ASCII character hexidecimal 0xNN. '\0nnn' is the ASCII character octal nnn. You could build a regex to handle these, perhaps, such as: my %escape = map { ( chr($_) => eval '"\\'.chr($_).'"'\|\|undef ) } 0 .. + 127; sub interpolate { my ($s) = @_; $s =~ s/\\c(.)/chr(ord(lc($1))-ord('`'))/ge; $s =~ s/\\x([a-fA-F0-9]{2})/chr(hex($1))/ge; $s =~ s/\\0([0-9]{1,3})/chr(oct($1))/ge; $s =~ s/\\0/\0/g; $s =~ s/\\(.)/$escape{$1}/gs; return $s; } [download]	[reply] [d/l]
Re: Selective string interpolation by ton (Friar) on Jun 29, 2001 at 05:02 UTC
I've posted my current code at Undumper. Any other feedback is much appreciated. -Ton ----- Be bloody, bold, and resolute; laugh to scorn The power of man...	[reply]
Re: Re: Selective string interpolation by merlyn (Sage) on Jun 29, 2001 at 08:59 UTC
You're not handling blessed items yet, and there's a much simpler way to write "listy" things. I'll take your inspiration and generate a version for a Linux Magazine article, crediting you... how do you want to be listed? -- Randal L. Schwartz, Perl hacker	[reply]


Think about Loose Coupling
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