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

Dear monks, 
use strict;
use warnings;
my $str = '6AG3_608_FGG_20100124_20120923418_20126254447_201262512026.
+txt';
$str =~ m/(.*)(_\d{11,}?.*)(\.\w+)/;
print $1, "\n";
print $2, "\n";
print $3, "\n";

[download]

prints 6AG3_608_FGG_20100124_20120923418_20126254447
_201262512026
.txt


But i want it to print
6AG3_608_FGG_20100124
_20120923418_20126254447_201262512026
.txt


Basically the filename gets appened with "_timestamp" after the YYYMMDD part everytime when it gets processed. i want to strip out the time stamps alone.


What i am doing wrong here?

Any help is much appreciated and thanks.

Replies are listed 'Best First'.
Re: why my reg ex matches greedy?
by tobyink (Canon) on Jun 25, 2012 at 21:33 UTC

    The (.*) part is greedy because you've not used the ungreedy quantifier. The ungreedy version is (.*?).

    perl -E'sub Monkey::do{say$_,for@_,do{($monkey=[caller(0)]->[3])=~s{::}{ }and$monkey}}"Monkey say"->Monkey::do'
[reply]
[d/l]
[select]
Re: why my reg ex matches greedy?
by McA (Priest) on Jun 25, 2012 at 20:44 UTC
    Hi,
    probably that is what you want:
    use strict;
use warnings;
my $str = '6AG3_608_FGG_20100124_20120923418_20126254447_201262512026.
+txt';
$str =~ s/_\d{11,}//g;
print $str, "\n";

    [download]
[reply]
[d/l]
      hi McA, thanks. yes that is what eventually i would need. but i would like to understand the reg ex to extract the pattern.
[reply]
        Ok ok ok,
        then take this: 
        use strict;
use warnings;
my $str = '6AG3_608_FGG_20100124_20120923418_20126254447_201262512026.
+txt';
$str =~ m/(.*?)(_\d{11,}?.*)(\.\w+)/;
print $1, "\n";
print $2, "\n";
print $3, "\n";

        [download]
[reply]
[d/l]
Re: why my reg ex matches greedy?
by roboticus (Chancellor) on Jun 25, 2012 at 20:19 UTC

    Inperl:

    You can't just make up syntax and expect perl to know what you want. Read perlre, then read it a couple more times, then you should be able to figure out how to tell perl what you're looking for.

    ...roboticus

    When your only tool is a hammer, all problems look like your thumb.

[reply]

      i did not make my own syntax and expect perl to understand it. it is just that i do not know what i was doing wrong over there and trying to seek help.

[reply]

        Well, clearly I'm an idiot. I thought I'd drop a mention of YAPE::Regex::Explain to show how to figure out what a regular expression is saying, so I could point out the "invented" bit. But I find that the bit I thought was "invented" seems fine. Sorry about that. When I run:

        use YAPE::Regex::Explain;
print YAPE::Regex::Explain->new(qr/(.*)(_\d{11,}?.*)(\.\w+)/)->explain
+();

        [download]

        I get:

        Read more... (3 kB)

        And I thought the \d{11,}? was the invented bit. I'll have to play with that sometime.

        ...roboticus

        When your only tool is a hammer, all problems look like your thumb.

[reply]
[d/l]
[select]

Back to Seekers of Perl Wisdom