alexx1523 has asked for the wisdom of the Perl Monks concerning the following question:

Why doesn't <STDIN> initialize and fill $_ in the following control block?

until(<STDIN> =~ /exit|quit|(^\s*$)/i) { }

I ended up leaving until(<STDIN>) by it's lonesome, then assigning $scalar = $_, then matching it to the above regex. Logic would dictate that there would be a more elegant solution. Thanks in advance!

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Re: $_ unitialized
by ikegami (Patriarch) on Aug 23, 2009 at 14:41 UTC

    Why doesn't <STDIN> initialize and fill $_ in the following control block?

    Because <STDIN> never changes $_. 

    while (<$fh>) { ... }

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    is short for 
    while (defined($_ = <$fh>)) { ... }

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    But since you don't have something of the form 
    while (<$fh>) { ... }

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    you never assign anything to $_. 
    while (<STDIN>) {
   s/\s+$//;
   last if /^(?:exit|quit)?$/i;
   ...
}

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Re: $_ unitialized
by Anonymous Monk on Aug 23, 2009 at 00:43 UTC
    Because you are using =~ 
    until(!defined($_ = <STDIN>) and /exit|quit|(^\s*$)/i) {
}

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    or
    while(<STDIN>){
    last if /exit|quit|(^\s*$)/i;
}

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      Did you mean "or" ( s/and/or ) in your first example?

      It's pretty hard for $_ to be both (!defined and anything).

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      Also because you are using until block
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