Is this normal

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

Hello. Why this is not returning 0 when the regex is false?

sub TestIt
{
  my ($p1,$p2,$p3,$p4)=@_;

  print "p1=$p1,p2=$p2,p3=$p3,p4=$p4\n";
}

my ($a1,$a2,$a3,$a4)=(1,2,3,4);

&TestIt($a1,$a2,$a3=~m/2/,$a4);
[download]

when $a3=~m/3/ every thing is ok, but when it is false it is not parsing 0. And the parameters is 1 less. When i use $a2==3 it parse the 0. Can someone explain it to me?

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Re: Is this normal by toolic (Bishop) on Jan 06, 2012 at 15:24 UTC
If you want the match to return 1 if successful, and 0 if it fails, you can use the ternary operator: `&TestIt($a1,$a2, ($a3 =~ m/2/) ? 1 : 0 ,$a4);` [download]	[reply] [d/l]
Re: Is this normal by JavaFan (Canon) on Jan 06, 2012 at 15:20 UTC
You're making two mistakes: You're calling the match in list context, so an empty list is returned, reducing the number of passed parameters. Even when called in scalar context, a non-match does not return 0. It returns the empty string (most Perl build-ins that return either a true or a false value, return 1 or "")	[reply]
Re^2: Is this normal by dave_the_m (Monsignor) on Jan 06, 2012 at 23:30 UTC
a non-match does not return 0. It returns the empty string Strictly speaking, it returns PL_sv_no, which has both a numerical value of 0 and a string value of "": `$ perl5140 -MDevel::Peek -e 'Dump scalar(/x/)' SV = PVNV(0x275ee10) at 0xa26500 REFCNT = 2147483647 FLAGS = (IOK,NOK,POK,READONLY,pIOK,pNOK,pPOK) IV = 0 NV = 0 PV = 0x275ee00 ""\0 CUR = 0 LEN = 16` [download] Dave.	[reply] [d/l]
Re^3: Is this normal by JavaFan (Canon) on Jan 07, 2012 at 08:45 UTC
You are correct. However, the OP is printing out the values, so the string value will be taken.	[reply]
Re: Is this normal by roboticus (Chancellor) on Jan 06, 2012 at 14:55 UTC
himik: I'm guessing that it's because you're calling the m operator in list context rather than scalar context. Perhaps it would work if you try: `TestIt($a1, $a2, scalar($a3=~m/2/), $a4);` [download] ...roboticus When your only tool is a hammer, all problems look like your thumb.	[reply] [d/l]