Multiple Test Regex Does not work the way I expect

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

Hey all, I can't understand the behaviour of my code... Here is my code

$hash = {
"s" => "",
"d" => "19.28.18.28",
"p1" => "",
"p2" => "88"
};

$s="192.168.3.79";
$d="19.28.18.28";
$p1="3269";
$p2="88";


print $s." -> ".$$hash{"s"}."\n";
if ( $s =~ $$hash{ "s" }) { print "\t1 ok\n";}else { print "\t1 NOK\n"
+;}

print $d." -> ".$$hash{"d"}."\n";
if ($d =~ $$hash{ "d" }){ print "\t2 ok\n";}else{ print "\t2 NOK\n";}

print $p1." -> ".$$hash{"p1"}."\n";
if ($p1 =~ $$hash{ "p1"}){ print "\t3 ok\n";}else{ print "\t3 NOK\n";}

print $p2." -> ".$$hash{"p2"}."\n";
if($p2 =~ $$hash{ "p2" }) { print "\t4 ok\n";}else { print "\t4 NOK\n"
+;}
[download]

Output

192.168.3.79 ->
1 ok
19.28.18.28 -> 19.28.18.28
2 ok
3269 ->
3 NOK
88 -> 88
4 ok
[download]

And when I comment the second test (if ($d =~ $$hash{ "d" }){), it prints:

Output

192.168.3.79 ->
1 ok
19.28.18.28 -> 19.28.18.28
3269 ->
3 ok
88 -> 88
4 ok
[download]

Why the third test could be one time true and the other time false ?

Thanks

Comment on Multiple Test Regex Does not work the way I expect Select or Download Code

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Re: Multiple Test Regex Does not work the way I expect by almut (Canon) on Oct 28, 2009 at 11:38 UTC
See perlop: `m/PATTERN/cgimosx (...) If the PATTERN evaluates to the empty string, the last successfull +y matched regular expression is used instead.` [download] Then, contemplate on what the effects of this (somewhat odd) feature are with your `$$hash{"p1"}` being empty... ___ P.S.: you'd typically write `$s =~ /.../;` (i.e. use an explicit pattern delimiter) even though Binding Operators says `If the right argument is an expression rather than a search patter +n, substitution, or transliteration, it is interpreted as a search pattern at run t +ime.` [download] P.P.S.: also note that the dots in a pattern like `/19.28.18.28/` are regex metacharacters, so maybe you want to use quotemeta (or rather simply use `eq` string comparison...?)	[reply] [d/l] [select]
Re^2: Multiple Test Regex Does not work the way I expect by stunbox (Initiate) on Oct 28, 2009 at 12:47 UTC
Thanks a lot dude, I added parantheses like they said in the doc you linked at. `if ($p1 =~ /$$hash{ "p1" }()/)` Thanks also for the quotemeta, I'll add it too.	[reply] [d/l]
Re: Multiple Test Regex Does not work the way I expect by biohisham (Priest) on Oct 28, 2009 at 14:16 UTC
You have provided your variables as stringified hash keys as well as test variables and then you're testing their existence against hash values, but $hash{'s'} and $hash{'p1'} values are "empty" still the tests results are not consistent, condsider: `if ( $s =~ $$hash{ "s" }) { print "\t1 ok\n";}else { print "\t1 NOK\n"; if ($d =~ $$hash{ "p1" }){ print "\t2 ok\n";}else{ print "\t2 NOK\n";} !` [download] and you get back: `1 ok #is returned even when the hash doesn't have a corresponding valu +e for $s. 3 NOK #this works correct for $p1?` [download] Since you have used strings, you better use the string comparison operator "eq" and not the =~, and I bet you got tired of the excessive concatenation, use ' ' around the hash keys instead of " " and you would've been saved the trouble... #!/usr/local/bin/perl #title "Multiple Test Regex Does not work the way I expect"; #see the '' around hash keys.. $hash = { "s" => "", "d" => "19.28.18.28", "p1" => "", "p2" => "88" }; $s="192.168.3.79"; $d="19.28.18.28"; $p1="3269"; $p2="88"; print "$s -> $$hash{'s'}\n"; if ( $s eq $$hash{ "s" }) { print "\t1 ok\n"; }else { print "\t1 NOK\n"; } print "$d -> $$hash{'d'}\n"; if ($d eq $$hash{ "d" }){ print "\t2 ok\n"; }else{ print "\t2 NOK\n"; } print "$p1 -> $$hash{'p1'}\n"; if ($p1 eq $$hash{ "p1"}){ print "\t3 ok\n"; }else{ print "\t3 NOK\n"; } print "$p2 -> $$hash{'p2'}\n"; if($p2 eq $$hash{ "p2" }) { print "\t4 ok\n"; }else { print "\t4 NOK\n"; } [download] Excellence is an Endeavor of Persistence. Chance Favors a Prepared Mind.	[reply] [d/l] [select]