in reply to Re^5: AND and OR on Regular Expressions
in thread AND and OR on Regular Expressions

Some examples: 
    $_ = "foo bar foo";
    $pat1 = "(foo)";
    $pat2 = "(bar)";
    /$pat1/ && /$pat2/;          # Sets $1 (twice).
    /^(?=.*?$pat1)(?=.*?$pat2)/; # Sets $1 and $2.

    $pat1 = "(foo)";
    $pat2 = "(baz)";
    /$pat1/ && /$pat2/;          # Sets $1.
    /^(?=.*?$pat1)(?=.*?$pat2)/; # Doesn't set $1 or $2.

    $pat1 = "(foo)";
    $pat2 = "( )\\g{1}";
    /$pat1/ && /$pat2/;          # No match.
    /^(?=.*?$pat1)(?=.*?$pat2)/; # Match!

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As for the leading ^ - it only has a speed influence, and only if there's no match. But it can be a significant speed difference if the string is long, so it's better not to omit it.

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Re^7: AND and OR on Regular Expressions
by ikegami (Patriarch) on Aug 26, 2009 at 00:50 UTC

    So "yes".

    You're missing the line that initialises $_ to something "foo" for the second block.

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      I'm not missing that line. All matches are against the same $_.
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        Then look again.

        Are you are your saying your comments are wrong 

        /$pat1/ && /$pat2/;          # Sets $1 (twice).
/$pat1/ && /$pat2/;          # Sets $1.

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        /^(?=.*?$pat1)(?=.*?$pat2)/; # Sets $1 and $2.
/^(?=.*?$pat1)(?=.*?$pat2)/; # Doesn't set $1 or $2.

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        And that you repeated 4 lines of code for nothing? 

            $pat1 = "(foo)";
    $pat2 = "(bar)";
    /$pat1/ && /$pat2/;
    /^(?=.*?$pat1)(?=.*?$pat2)/;

    $pat1 = "(foo)";
    $pat2 = "(baz)";
    /$pat1/ && /$pat2/;
    /^(?=.*?$pat1)(?=.*?$pat2)/;

        [download]

        I swear I checked that a million times first. I'm blind! Needless to say, it would have been clearer to change $_ instead.

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