Executing a "/foo/flags" regex from a string

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

I wish to take a string like "/regex/i" (say, from the command line) and make a regex object with qr that I can execute just like I'd written that in the program text. I'm not sure about the best way to do it. I tried:

if ($search_term =~ m[^/.*/\w*$]) {
    # if it is in the form "/foo/x" or whatever, treat it as
    # though it had been specified in Perl program text
    $search_re = qr($search_term);
}
[download]

If I input /tree/i, it returns a regex (?^:/tree/i) that searches for "/tree/i", which isn't what I want. I want something like (?^i:tree) which will match "tree" or "Tree" or "Street". That I can get using a string eval():

$search_re = eval("qr${search_term}");
[download]

Is there a better way to do this? This is a personal command-line tool, so I'm not really worried about malicious input to the string eval; but if there's a better way I'd like to know for the future.

Thanks,
Aaron

Comment on Executing a "/foo/flags" regex from a string Select or Download Code

Replies are listed 'Best First'.
Re: Executing a "/foo/flags" regex from a string by Rhandom (Curate) on Dec 30, 2015 at 01:59 UTC
Here is a small snippet that should do what you were asking for (more or less): `perl -E 'my $str = "/regex/i"; my ($pat, $flags) = $str =~ m{^/(.+)/([imsx]*)\z} ? ($1, $2) : die "Bad regex"; my $qr = qr/(?$flags:$pat)/; say qq{Matched "$_" with $qr} for grep {$_ =~ $qr} qw(foo bar baz reGex)' Matched "reGex" with (?^u:(?i:regex))` [download] my @a=qw(random brilliant braindead); print $a[rand(@a)];	[reply] [d/l]
Re^2: Executing a "/foo/flags" regex from a string by Radiola (Monk) on Dec 30, 2015 at 18:05 UTC
Ah, OK. I guess there's nothing more to the syntax of `/regex/flags` than, uh, the regex and the flags, so you don't risk losing anything by parcelling them out and putting them back together like that. Thanks! - Aaron	[reply]
Re: Executing a "/foo/flags" regex from a string (qr flags) by Anonymous Monk on Dec 30, 2015 at 01:52 UTC
qr can do it as perlre syntax allows (?i) the same as /i `$ perl -le " print int q{shoes} =~ /SHOES/ " 0 $ perl -le " print int q{shoes} =~ /SHOES/i " 1 $ perl -le " print int q{shoes} =~ /(?i)SHOES/ " 1` [download] App::Ack uses this trick You can use `eval { no re qw/eval/; qr/$regex/ };` to see if the regex compiles See also Text::Glob#glob_to_regex	[reply] [d/l]