Pattern matching

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

im a newbie to perl and i want to extract tags from the following:

[check-->PERLMONKS_001]
[check-->PERLMONKS_002]
[check-->PERLMONKS_003]
[download]

The o/p should be

PERLMONKS_001
PERLMONKS_002
PERLMONKS_003
[download]

The snippet im trying is

    if($array[$i] =~ /Check-->\s*\d+$/)
            {
                $Output= $1;
[download]

i dont know where im making mistake ..

Comment on Pattern matching Select or Download Code

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Re: Pattern matching by Ratazong (Monsignor) on Jan 13, 2012 at 10:57 UTC
Dear stallion, one advantage of perl is that you can try things out pretty fast. So you could just add a `print "$output\n";` [download] to your snippet and see whether it works or not. And if it doesn't work at the beginning (it often doesn't), you could use that snippet to iteratively come to a solution. For example you could first try to extract the 3-digit-number. One hint: if you want to use $1, you need to capture () something from the regular expression. The things you want to capture should be written in round brackets `( )`. Extracting the number at the end could look like `$array[$i] =~ /(\d+)$/;` [download] HTH, Rata : see perlretut (section on extracting matches).	[reply] [d/l] [select]
Re: Pattern matching by ww (Archbishop) on Jan 13, 2012 at 14:59 UTC
You appear to be using a C-style loop: `if($array[$i] =~ /Check-->\s\d+$/) # ^ C style loop counter?` [download] Sometimes, that's the (only) way to go, but generally, a more idomatic approach is: `for my $array(@array) { chomp $array; # may be unnecessary for your aplication if ($array =~ /check-->(\S\d+)(?:\])$/i) { # \S Not-a-space, / +i case insensitive # ^ also un-needed, for data shown, +but a precaution # against some possible elements in +your __DATA__ my $output = $1; # Good approach; avoids reusing a left-ove +r match` [download]	[reply] [d/l] [select]
Re: Pattern matching by hbm (Hermit) on Jan 13, 2012 at 14:11 UTC
One apparent mistake is that your expression starts with 'C' but your data start with 'c'. Perhaps you want the `//i` (ignore case) modifier.	[reply] [d/l]
Re: Pattern matching by umasuresh (Hermit) on Jan 13, 2012 at 10:48 UTC
You are capturing the match, try this untested: `if($line =~ /check.\>\s([^>]+)$/) { print "$1\n"; }` [download]	[reply] [d/l]
Re^2: Pattern matching by pklausner (Scribe) on Jan 13, 2012 at 14:20 UTC
Yes, the sub-match parenthesis are missing. And the PERLMONKS_ part. And the case of Check. Should be (still not tested): `if($array[$i] =~ /check-->\s(\S\d+)$/) { $Output= $1;` [download]	[reply] [d/l]