in reply to Easy Reference for Contexts

m/.../ returns true or false in scalar context 
m/.../g give you a list of matches in list context 
m/(...)/ can populate an array with whatever gets captured... (??)
 
while( ) i.e. inside parenthesis is evaluated in scalar context? 
foreach( ) i.e. inside parenthesis is evaluated in list context?
 
<STDIN> returns the next line of input in list context

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Well ... most of this can be tested interactively.

The inside context with wantarray the outside context behavior with print, print scalar and a void call.

For instance I doubted that scalar m// returns true or false (those identifiers don't exist in Perl), I thought it's the number of matches returned.

But I was wrong: :) 

  DB<23> $_="aaa"
 
  DB<24> print scalar m/a/
1

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Cheers Rolf

UPDATE: Forgot to mention, you can also check the prototype for most builtins: 

 perl -e 'print prototype "CORE::push","\n"'
\@@

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which is more complex than just void, list and scalar... check out perlsub for details.

And some builtins (like map) have such a "rich" syntax that they can't be expressed with prototypes.

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Re^2: Easy Reference for Contexts
by tchrist (Pilgrim) on Apr 14, 2011 at 19:27 UTC
    For instance I doubted that scalar m// returns true or false (those identifiers don't exist in Perl), I thought it's the number of matches returned.

    But I was wrong: :) 

      DB<23> $_="aaa"
 
  DB<24> print scalar m/a/
1

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    Anything in Perl is true or false. Or rather, ANYTHING is true but undef is false. 😋

    Like the relops, m//, s///, and y/// can all return the magical false value, that secret special value that nobody talks about:

    % perl -wle 'printf "got %d matches\n", scalar ANYTHING =~ /nothing/'
    got 0 matches
    So I shan’t, either. 😜
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      > Or rather, ANYTHING is true but undef is false.

      Many things in Perl are evaluated to false in boolean context, not only undef.

      Cheers Rolf

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[d/l]
        Tom is right. ANYTHING is true: 
        $ perl -E 'say +ANYTHING ? "true" : "false"'
true

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