in reply to using multiple conditionals in a while(test)

In a limited set of cases, Perl applies special treatment to while loops. One such case is when the condition is a read from a file.

In these special cases while( COND ) { gets translated into while( defined( local $_ = COND ) ) {.

But for this to happen, COND has to be a 'simple' condition.

Your example:

 while( (<FP>) && (!/^_stop\n/) ) {

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doesn't satisfy this requirement.

To compensate, you would have to explicitly code that to use $_. Ie.

 while( defined( local $_ = <FP> ) and  ! /^_stop\n/ ) {

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Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
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Re^2: using multiple conditionals in a while(test)
by jwkrahn (Abbot) on Dec 04, 2010 at 07:12 UTC
    gets translated into while( defined( local $_ = COND ) ) {.

    Not quite.    The $_ variable is NOT localized in a while loop: 

    $ echo "one           
two           
three      
four       
five       
six        
seven            
eight       
nine        
ten" | perl -e'
while ( <> ) {
    last if /seven/;
    }            
print "$.: $_\n";
'
7: seven

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[d/l]
[select]

      You're right. 

      C:\test>perl -MO=Deparse -e"while( <> ) { print }"
while (defined($_ = <ARGV>)) {
    print $_;
}
-e syntax OK

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      But if you're doing it yourself, it's as well to.

      Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
      "Science is about questioning the status quo. Questioning authority".
      In the absence of evidence, opinion is indistinguishable from prejudice.
[reply]
[d/l]
        I see. I had a feeling it was a special case.
        Excellent explanations and examples.
        Thank you.
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