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

This ought to be simple, but I can't figure it out...
My script is a web form that accepts text from the form and drops it into a mysql database table. Certain characters have to be escaped or mysql chokes or does the odd thing. One is the backslash...I'm trying to do this:
s/\/\\/g;
which doesn't work.
I tried various convolutions, such as:
s/\Q/\E/\\/g;
which compiles ;-) but doesn't add the additional backslash. Where am I brain damaged on this?

Replies are listed 'Best First'.
Re: escaping the backslash
by chromatic (Archbishop) on Apr 29, 2003 at 20:59 UTC

    Consider using DBI's quote() method instead, or, better yet, placeholders.

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Re: escaping the backslash
by Jenda (Abbot) on Apr 29, 2003 at 21:13 UTC

    chromatic is right, you should use the quote() or even better the placeholders. This is just to explain why what you tried didn't work.

    The replacement string in a s/// is basicaly just a doublequoted string. In such a string if you want to include a literal backslash you have to escape it:

    print "A backslash \\ is here\n";

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    In your case you need two literal backslashes so you have to enter four in the replacement.

    Second, the list of characters that need to be escaped in a regular expression is even longer than in a doublequoted string. What they both have in common is that you have to type two backslashes if you want to get a single literal backslash. So the line should look like this: 

    s/\\/\\\\/g;

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    or better 
    s{\\}{\\\\}g ;

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    (The second version is a bit more readable.)

    Jenda
    Always code as if the guy who ends up maintaining your code will be a violent psychopath who knows where you live.
       -- Rick Osborne

    Edit by castaway: Closed small tag in signature

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[d/l]
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      Jenda, chromatic;
      Thanks for the advice. I can see in Jenda's explanation why the substitution wasn't working. I took a crack at the quote() method, but it turns out the text being dumped on the form has newlines, which is another bag of worms for quote(). ;-)
      Since it's time to go home, I'll take a shot with the placeholders tomorrow. Thanks for the great assistance.
      joedoc
[reply]
        Your newline problem is probably related to the output record separator. You can just assign to it to change the default behaviour.

        $, - output field separator (default: comma)
        $\ - output record separator (default: newline)
        $" - list separator (default: space)
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