Regex in string to be used for matching.

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

I figured this out the other day but today when I want to use it cannot find the notes I though I had saved. I have a regex loaded into a string which I need to use to do some matching. I've tried the following -

$string = 'My Test Data';
$regex = 'm/\btest\b/i';
if ($string =~ $regex){print "It Works!\n"}else{print "No joy!\n"};
[download]

and

$string = 'My Test Data';
$regex = 'm/\bTest\b/i';
$stmt = 'if ($string =~ $regex){print "It Works!\n"}else{print "No joy
+!\n"}';
eval $stmt;
[download]

Comment on Regex in string to be used for matching. Select or Download Code

Replies are listed 'Best First'.
Re: Regex in string to be used for matching. by ikegami (Patriarch) on Nov 09, 2009 at 20:57 UTC
$regex contains a match operator (Perl source code), not a regex pattern. `$string = 'My Test Data'; $regex = '(?i)\btest\b'; print $string =~ m/$regex/ ? "Match\n" : "No match\n";` [download] or just `$string = 'My Test Data'; $regex = '(?i)\btest\b'; print $string =~ $regex ? "Match\n" : "No match\n";` [download] m// is implied if the RHS of `=~` is not one of the ops that are affected by `=~`.	[reply] [d/l] [select]
Re^2: Regex in string to be used for matching. by Anonymous Monk on Nov 09, 2009 at 22:02 UTC
$regex contains a match operator (Perl source code), not a regex pattern. Its just a string `my $regex = qr!(?i)\btest\b!;` [download]	[reply] [d/l]
Re^3: Regex in string to be used for matching. by ikegami (Patriarch) on Nov 09, 2009 at 22:25 UTC
The match operator will happily interpolate a pattern stored as a string. Compiled patterns have only existed since 5.6. `qr//` is not necessary. In fact, using qr// makes no sense here. If there's no reason for the pattern to be a string, you might as well just do `$string = 'My Test Data'; print $string =~ m/\btest\b/i ? "Match\n" : "No match\n";` [download] But I bet there's a reason it's a string here. If so, you'd do `$string = 'My Test Data'; $regex = '(?i)\btest\b'; print $string =~ $regex ? "Match\n" : "No match\n";` [download] If you were planning on using `$regex` repeatedly, then `qr//` could become useful.	[reply] [d/l] [select]