Beefy Boxes and Bandwidth Generously Provided by pair Networks
good chemistry is complicated,
and a little bit messy -LW

Re^2: The return value of m// (clues)

by sophate (Beadle)
on Apr 23, 2012 at 05:25 UTC ( #966524=note: print w/replies, xml ) Need Help??

in reply to Re: The return value of m// (clues)
in thread The return value of m//

Really interesting! I changed the script to:

#!/usr/bin/perl use strict; use warnings; my $a=" 456 789 123 456 789 "; my $count; $count = $a =~ /\d+/g ; print "$count\n"; my @a = $a =~ /\d+/g ; $count = @a; print "@a\n"; print "$count\n"; $count = () = $a =~ /\d+/g ; print "$count\n";

The results are:<\p>

1 789 123 456 789 4 5

Could you please advise why the 1st digit group is gone the first time i call $a =~ /\d+/g ?

Replies are listed 'Best First'.
Re^3: The return value of m// (clues)
by quester (Vicar) on Apr 23, 2012 at 07:04 UTC

    Hint: look for the phrase "search position" in perlop. Also consider that scalar global matches are typically used in loops, for example

    for my $match ($a =~ /\d+/g) { print "$match\n" }
Re^3: The return value of m// (clues)
by kcott (Chancellor) on Apr 23, 2012 at 07:56 UTC

    When you use the g modifier, it keeps track of its last match. In the first RE (scalar context), 456 is matched: your count indicates a single match (see code below for actual value). In the second RE (list context), the remaining four sets of digits are matched. You can use pos to reset the last match position.

    $ perl -Mstrict -Mwarnings -e ' > my $a=" 456 789 123 456 789 "; > my $count; > $count = $a =~ /\d+/g ; > print "$count\n"; > print "${^MATCH}\n"; > pos($a) = 0; > my @a = $a =~ /\d+/g ; > $count = @a; > print "@a\n"; > print "$count\n"; > ' 1 456 456 789 123 456 789 5

    ${^MATCH} is described in perlvar.

    -- Ken

      Thanks so much !! It's great to learn more about how g behaves :-)

Re^3: The return value of m// (clues)
by bimleshsharma (Beadle) on Apr 23, 2012 at 07:47 UTC

    Really i could not understand but the code

    $count = $a =~ /\d+/g ; vs. $count = () = $a =~ /\d+/g ;

    is an issue.

Log In?

What's my password?
Create A New User
Node Status?
node history
Node Type: note [id://966524]
[zentara]: perf
[marto]: X86_instruction_li stings
[marto]: Illegal_opcode
[zentara]: marto arn't those NSA secrets? :-)
[marto]: not if you keep telling people :P
[zentara]: I had to disable hyperthreading on my machine because of that.
[Discipulus]: thanks marto but... at the moment this seems a bit beyond my faculties.. ;=)
[zentara]: a thread goes into a wait state after emitting a wait to all other threads. It locks up a machine completely.
[marto]: if you mean the recent hyperthreading bug, I don't think that's NSA related?
[zentara]: s/thread/cpu/

How do I use this? | Other CB clients
Other Users?
Others surveying the Monastery: (10)
As of 2017-07-28 12:08 GMT
Find Nodes?
    Voting Booth?
    I came, I saw, I ...

    Results (428 votes). Check out past polls.