using && with regex in an if() statement

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

Greetings, monks. I have come in search of wisdom that I have not found anywhere else; neither the the Camel book nor Googling has come up with an answer to my question and I hope that it may be answered here. I am trying to find multiple words in a sentence, and if I find them, act accordingly. To wit, I wrote:

if ($sentence =~ /foo/gis && $sentence =~ /bar/gis)
{
   # do something further with $sentence 
}
[download]

But it is wrong, the second expression is always false, even if the sentence does contain a "bar". I rewrote it to say:

if ($sentence =~ /foo/gis)
{
   if ($sentence =~ /bar/gis)
   {
      # now do something with the sentence
   }
}
[download]

but that doesn't work either! The only way I could get it to work was:

if ($sentence =~ /foo/gis)
{
    my $final_test = $sentence;
    if ($final_test =~ /bar/gis)
    {
       # *now* do something with the sentence...
    }
}
[download]

I apologize if this is a real "duh" question; it seemed like it would make sense to me (a C++ programmer) but the second try really confused me as I figured it surely couldn't fail, it was just doing another search. I beg wisdom and mercy for my cluelessness. Thank you, Tacho

Comment on using && with regex in an if() statement Select or Download Code

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Re: using && with regex in an if() statement by Roy Johnson (Monsignor) on Mar 14, 2006 at 17:02 UTC
What do you actually have in `$sentence`? I note that you're using /g on both matches, so the 2nd will start searching where the first left off, rather than at the beginning. Your "fixed" version circumvents that behavior (and makes me wonder what you hope to accomplish with the /g modifier). This works as anyone would expect it to: `my $sentence = 'I got a foo and a bar in me'; if ($sentence =~ /foo/gis && $sentence =~ /bar/gis) { print "I'm doing something with $sentence\n"; }` [download] whereas reversing bar and foo in the sentence cause the test to fail. Caution: Contents may have been coded under pressure.	[reply] [d/l] [select]
Re^2: using && with regex in an if() statement by Tachoknight (Initiate) on Mar 14, 2006 at 22:20 UTC
Yes, the problem was the /g....I removed it and all was well. I am trying to create a "natural language" parser, and a "real" sentence would have been something like Fred bought the car or The car was bought by Fred So I was searching for car and bought, but I thought /g would find the words globally through the text, regardless of position. I apologize: I'm a real newbie with regular expressions; most of my Perl work has not involved any real searches to date, but that has now changed and I'm going through that chapter that I always kinda meant to get back to someday to figure out.... Thanks again! Tacho	[reply]
Re: using && with regex in an if() statement by kvale (Monsignor) on Mar 14, 2006 at 17:00 UTC
The snippet `my $sentence = "foo bar"; if ($sentence =~ /foo/gis && $sentence =~ /bar/gis) { print "Got here\n"; }` [download] prints "Got here", so perhaps check your sentence again. -Mark	[reply] [d/l]
Re: using && with regex in an if() statement by QM (Parson) on Mar 14, 2006 at 17:04 UTC
Update: I think Roy Johnson has it right -- watch out for the `/g` flag. Something else is wrong: >perl -demo Loading DB routines from perl5db.pl version 1.28 Editor support available. Enter h or `h h' for help, or `perldoc perldebug' for more help. main::(-e:1): mo DB<1> $sentence = 'sdfsdfsdf foo asdfklj bar ;alkdjdf' DB<2> x $sentence 0 'sdfsdfsdf foo asdfklj bar ;alkdjdf' DB<3> p "match" if $sentence =~ /foo/ && $sentence =~ /bar/ match [download] Either `$sentence` doesn't contain what you think it does, or you haven't run the code you posted. Or you need the `/m` flag. Or something else. Please post the actual code (or better, a minimal example that behaves the same way), including the value of the variable involved in the match. -QM -- Quantum Mechanics: The dreams stuff is made of	[reply] [d/l] [select]
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