in reply to Re: Re: relaying arguments using system call
in thread relaying arguments using system call

Hi tachyon, thanks once again.

I wonder if you have time if you could help me unravel what you're doing!
If I'm correct you are saying $var minus $ILLEGAL_CHARS equals acceptable $var. However I don't understand the expression   $var = ";rm -rf /*;";   also   qr/[^A-Za-z0-9._-]/;   Am I right in thinking that   qr//;  allows you to assign the regex to the variable, rather than have it act upon the variable?

Also it looks as though the $ILLEGAL_CHARS are the one's that I would wish to keep (as per the sense of your explanation) but they are being removed from the variable.

I'm sorry if this all seems to be silly or uninformed - I am doing my best to make sense of it and I hope that by not flinching in asking silly questions now I might learn enough to start asking sensible questions in the first place!!

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Re: Re: Re: Re: relaying arguments using system call
by benn (Vicar) on Mar 21, 2003 at 14:34 UTC
    The expression $var = ";rm -rf /*;"; is an example of dangerous input - if this was passed to 'system', the ';' would mark the end of the previous command, and then system would execute the 'rm' command.

    The qr/[^A-Za-z0-9._-\]/; expression creates a compiled regex - a variable with regex expressions in it that is 'ready to be used' in another regex.
    Note that the character class [^...] starts with a 'hat'. This reverses the class so that it refers to all characters except the ones in the class. So actually the expression says "$var minus anything that ISN'T that lot.
    This is often confusing I know, as the 'hat' is also used as an start-string anchor, but you get used to it :).
[reply]

      Nicely explained.

      cheers

      tachyon

      s&&rsenoyhcatreve&&&s&n.+t&"$'$`$\"$\&"&ee&&y&srve&&d&&print

[reply]

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