in reply to Re^2: Best practice for reading delimited file
in thread Best practice for reading delimited file

prematch is just a wordier name for $`

A considerable performance penalty by any other name doth make thine system slow all the same!

Edit: The documentation apparently doesn't mean what it appears to say.

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Re^4: Best practice for reading delimited file
by Kenosis (Priest) on Oct 16, 2013 at 17:58 UTC

    prematch is just a wordier name for $`

    $PREMATCH is the same as $` but it's not the same as ${^PREMATCH}:

    * $PREMATCH
* $`

The string preceding whatever was matched by the last
successful pattern match, not counting any matches hidden
within a BLOCK or eval enclosed by the current BLOCK.

The use of this variable anywhere in a program imposes a
considerable performance penalty on all regular expression
matches. To avoid this penalty, you can extract the same
substring by using @-. Starting with Perl v5.10.0, you can
use the /p match flag and the ${^PREMATCH} variable to do
the same thing for particular match operations.

    [download]

    Source: perlvar.

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      Ah, nifty!

      Since Perl v5.10.0, you can use the /p match operator flag and the ${^PREMATCH} , ${^MATCH} , and ${^POSTMATCH} variables instead so you only suffer the performance penalties.

      Is that sentence missing a "once" at the end perhaps?

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        I think it's missing "for this regexp, not for all regexps anywhere in your script+modules".

        Jenda
        Enoch was right!
        Enjoy the last years of Rome.

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        That certainly is a curiously obscure assertion, given the performance statements a bit later in the documentation. I think you're correct that something is missing here, but I'm not sure it's "once at the end".

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