Re: converting text expressions (like "1+1") to values

On Dec 29, 2:50 am, chas.ow...@xxxxxxxxx (Chas. Owens) wrote:
On Dec 28, 2007 10:15 AM, Adarsh Srivastava<Adarsh.Srivast...@xxxxxxxxxxxxxxxx> wrote:
Hello,

Is there any inbuilt/external function or library that can convert a text
expression (eg. "22 + 23") and evaluate the resulting value?( 45 in this
case).

snip

Well, the string form of eval will do this; however, it is very
dangerous. What if the string contained valid Perl code* to do
something on your system? Any time you use the string form of eval
you should first run the string through a regex make sure it only
contains things you expect it to. If the expressions are simple
arithmetic then this should suffice:

my $expr = get_expression(); #I don't know how you are getting "22 + 23"
die "bad expression: [$expr]" unless $expr =~ m{\A[ 0-9+-/*]+\z};
my $result = eval $expr;
die "got error [$@] when eval'ing [$expr]" if $@;

If you need to be able to call functions like sqrt, your regular
expression will become significantly more complex and it may be time
to look into writing a parser instead (especially if the names, call
signatures, or expected return values of the functions don't line up
with the standard Perl versions).

* imagine eval'ing the string "use File::Find; find sub { unlink }, $ENV{HOME};"

I am wondering if there are some methods which can let us free from
such things.
I mean if there is an embedded solution which can refuse unlink
function but accept normal (like math) functions?

thanks

.

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