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

Hello,

I would like to use a string (e.g. read from a file) as a piece of code in my perl program. For example, I read a string (e.g. $str="1..100,171,398..1000") then I would like to print all the numbers in the range represented by the string.

Thanks, Dave

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Re: use string as a piece of code
by moritz (Cardinal) on Jul 30, 2010 at 16:49 UTC
    It seems that Set::IntSpan can solve your problem without eval, provided you substitute the .. by - first.
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Re: use string as a piece of code
by SuicideJunkie (Vicar) on Jul 30, 2010 at 16:53 UTC

    You would be better served to parse that, and then do the loop, rather than just evaling arbitrary strings that may include Bobby Tables, or rm -rf *

    I suggest a series of simple regex:

    1. Remove everything that is not a digit, a comma or a '..'
    2. clean up leading/trailing commas and multiple commas in a row
    3. Validate (everything should in the expected form (number {comma or EOS}, or number dot-dot number {comma or EOS})
    4. split on commas
    5. For each item in the split, capture some digits followed by an optional '..' with more captured digits afterwards
    6. If there wasn't a '..', then just print $1, other wise, print $_ for $1..$2

    - SJ

    How to make perldoc.perl.org resizable too!
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Re: use string as a piece of code
by FunkyMonk (Bishop) on Jul 30, 2010 at 16:45 UTC
    eval.

    my $str = '1..3,10..14';

do_something($_) for eval $str;

    [download]

    Just be very sure that you trust whoever created the file you're reading from. What happens if it contains "system qw{rm -rf /}" (or the equivalent on your OS)?

    update: Added code

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      Thanks!

      A followup: my ranges are quite large (~500k numbers, usually in one or two blocks only, i.e. something like 1..20000,700000..1000000).

      What is the efficient way to simply print them out to a file?

      Maybe  for $i (1..20000,700000..1000000) {print "$i "}? I'm not sure if an array is actually created here... if it is, maybe it's not a good idea.

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