Re^2: qr// and user provided regex patterns...

Okay, I've managed to get this to work perfectly with a regular match (//) - but when I try to do a substitution(s///), the pattern fails to match anything - and no substitution is done. I'm calling the program like this: -r "s/matt/matthew/" -i -g, with the text 'matt, Matt'. Here is the code that processes the substitution bit:

if($options{r}){
    #variable grab, add flags to pattern if they exist.
    my $pattern = $options{r};
    $pattern .= 'g' if $options{g};
    $pattern .= 'i' if $options{i};
    $pattern .= 's' if $options{s};
    
    #compile that stuff with eval
    my $compd_pattern = eval "qr($pattern)" or die $@;
    
    print "Please enter the text you wish to run the pattern on: ";
    my $text = <STDIN>;
    chomp $text;
    
#do work and display
    if($text =~ $compd_pattern){
        print $text;
    }
    else{
        print "$pattern on \n\t{$text} Failed. ";
    }
} #end R FLAG
[download]

Comment on Re^2: qr// and user provided regex patterns... Download Code

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Re^3: qr// and user provided regex patterns... by JadeNB (Chaplain) on Aug 03, 2009 at 15:46 UTC
As toolic points out, `qr//` is meant to quote a pattern, not an entire substitution. If you want to pass in literal substitutions, rather than just patterns, then just `eval` at a different point: `eval "\$text =~ $pattern";` [download] By the way, ikegami suggested using `(?i:)` in place of a string-based `eval`. Since such `eval`s are always a cause for concern, and should be a cause for terror when run on user-provided input, are you sure that you considered the alternative properly before making your decision? If you're not happy with the inability of a `(?i:)`-type solution to handle substitutions, then you can probably just offer `--search` and `--replace --by` flags so that the user can specify directly what he or she wants.	[reply] [d/l] [select]
Re^3: qr// and user provided regex patterns... by ikegami (Patriarch) on Aug 04, 2009 at 03:24 UTC
It makes no sense to let the user specify /g for a match. You can't even use it on qr// because it makes no sense. ixsm are the four modifiers that apply to the pattern as opposed to the operator. The followign doesn't make much sense: `my $compd_pattern = eval "qr($pattern)" or die $@;` [download] It removes the ability of qr// to quote, which is what you want. The code should be `my $compd_pattern = qr($pattern);` [download] You say you have problems doing substitutions, but you didn't show us your attempt (despite your claim). You should have no problems using a qr// pattern in a substitution. `my $pat = ...; my $repl = ...; my $mods = ''; $mods .= 'i' if ...; $mods .= 's' if ...; $mods .= 'm' if ...; $mods .= 'x' if ...; my $re = qr/(?$mods:$pat)/; if (...) { s/$re/$repl/g; } else { s/$re/$repl/; }` [download]	[reply] [d/l] [select]
Re^4: qr// and user provided regex patterns... by JadeNB (Chaplain) on Aug 04, 2009 at 13:49 UTC
You say you have problems doing substitutions, but you didn't show us your attempt (despite your claim). You should have no problems using a qr// pattern in a substitution. I think that misterMatt's problem was that he was trying to stuff a substitution into a `qr//`, like: `my $substitution = 's/out/in/'; my $pattern = qr/$substitution/;` [download] which, naturally, doesn't work (well, doesn't cause a substitution, anyway).	[reply] [d/l] [select]
Re^3: qr// and user provided regex patterns... by toolic (Bishop) on Aug 02, 2009 at 13:51 UTC
I suspect that qr was not intended to be used on an entire subsitution operator like that. I believe it should only be used on the regular expression portion (left side) of the subsitution. See perlop. Here is an example script which uses `s///` as a command-line option: http://www.cpan.org/authors/id/F/FO/FORMAN/ren-regexp-1.5	[reply] [d/l]
Re^4: qr// and user provided regex patterns... by misterMatt (Novice) on Aug 02, 2009 at 21:00 UTC
so I pretty much will have to split it and evaluate it like this: eval("$text =~ s/$pa/$tx/$md"); It might be difficult splitting a regex that could contain multiple /'s. I'll have to adjust the program so the user enters the pattern, and replacement separately I guess.	[reply]


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