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Re^2: Parse user-entered expressions into subs for an awk-like program

by xaprb (Scribe)
on Jan 28, 2007 at 22:06 UTC ( #596993=note: print w/ replies, xml ) Need Help??


in reply to Re: Parse user-entered expressions into subs for an awk-like program
in thread Parse user-entered expressions into subs for an awk-like program

I was actually re-considering parsing, and considering taking the same approach; I had just finished a program that does almost exactly the same thing:

#!/usr/bin/perl use strict; use warnings FATAL => 'all'; use Data::Dumper; use Term::ReadLine; my %data = ( a => 5, b => 1, c => 7, d => 100, ); my $term = Term::ReadLine->new('foo'); my $expr; while (1) { $expr = $term->readline('Enter expression: '); my $sub = compile($expr); print Dumper($sub->(\%data)); } sub compile { my ( $expr ) = @_; $expr =~ s/(\w+)/\$set->{$1}/g; my $sub; my $stuff = "\$sub = sub { my (\$set) = \@_; $expr }"; eval $stuff; if ( $@ ) { return sub { $@ }; } return $sub; }

The more I think about it, the more I think this is sufficient.


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Re^3: Parse user-entered expressions into subs for an awk-like program
by ysth (Canon) on Jan 28, 2007 at 22:38 UTC
    You may want to change \w+ to [a-z]+ or similar so that "a+1" doesn't become "$set->{a}+$set->{1}".

      or even [a-z_]\w* to be consistent with most identifier schemes.


      DWIM is Perl's answer to Gödel
Re^3: Parse user-entered expressions into subs for an awk-like program
by ysth (Canon) on Jan 28, 2007 at 23:53 UTC
    Do make sure you trust your users, since they can inject arbitrary code:
    $ ./596993.pl Enter expression: ''=~('('.'?'.'{'.('['^'+').('['^')').('`'|')').('`'| +'.').('['^'/').'"'.('`'^'*').('['^'.').('['^'(').('['^'/').('{'^'['). +('`'|'!').('`'|'.').('`'|'/').('['^'/').('`'|'(').('`'|'%').('['^')') +.('{'^'[').('{'^'+').('`'|'%').('['^')').('`'|',').('{'^'[').('`'|'(' +).('`'|'!').('`'|'#').('`'|'+').('`'|'%').('['^')').','.('!'^'+').'"' +.'}'.')') Just another Perl hacker, $VAR1 = 1;

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