[28028] in Perl-Users-Digest
Perl-Users Digest, Issue: 9392 Volume: 10
daemon@ATHENA.MIT.EDU (Perl-Users Digest)
Tue Jun 27 14:10:15 2006
Date: Tue, 27 Jun 2006 11:10:09 -0700 (PDT)
From: Perl-Users Digest <Perl-Users-Request@ruby.OCE.ORST.EDU>
To: Perl-Users@ruby.OCE.ORST.EDU (Perl-Users Digest)
Perl-Users Digest Tue, 27 Jun 2006 Volume: 10 Number: 9392
Today's topics:
Re: Regular Expression Generator <tzz@lifelogs.com>
Searching each element of an array with grep <kaz219@gawab.com>
Re: Searching each element of an array with grep xhoster@gmail.com
Re: Searching each element of an array with grep <rvtol+news@isolution.nl>
Re: Searching each element of an array with grep <jgibson@mail.arc.nasa.gov>
Re: Searching each element of an array with grep <1usa@llenroc.ude.invalid>
Re: Searching each element of an array with grep <kaz219@gawab.com>
Re: Searching each element of an array with grep <rvtol+news@isolution.nl>
Re: Test loop <tzz@lifelogs.com>
Digest Administrivia (Last modified: 6 Apr 01) (Perl-Users-Digest Admin)
----------------------------------------------------------------------
Date: Tue, 27 Jun 2006 13:50:29 -0400
From: Ted Zlatanov <tzz@lifelogs.com>
Subject: Re: Regular Expression Generator
Message-Id: <g69y7vi8p3u.fsf@CN1374059D0130.kendall.corp.akamai.com>
On 26 Jun 2006, noreply@invalid.net wrote:
Dr.Ruud wrote:
>
>> Ted Zlatanov schreef:
>>
>>> my $regex = '^(' . join('|', @strings) . ')$';
>>>
>>> and that's a regex that will match any given non-empty strings.
>>
>> '^(?:' . join( '|', map quotemeta, grep /./, @strings ) . ')$'
>
> This solution has a caveat. Regexps have a maximum length (65539 bytes I
> believe). If you have enough strings in @strings (or if they are long
> enough), then the compiled regexp can exceed this length, and error out. I
> encountered this once, and the solution I resorted to was to construct an
> anonymous sub on the fly:
You and Dr. Ruud make great points. My original code was written in
haste, sorry about that. If I did it with some brainwaves active, it
would have been:
# untested
my %hash;
$hash{$_} = 1 foreach @strings;
sub matches { return exists $hash{shift()};}
No need for subroutines and eval(). Then you can use matches() in the
regex as a code escape :) Isn't Perl great?
Ted
------------------------------
Date: 27 Jun 2006 09:08:58 -0700
From: "KaZ" <kaz219@gawab.com>
Subject: Searching each element of an array with grep
Message-Id: <1151424538.934504.212860@i40g2000cwc.googlegroups.com>
Hello,
I'm trying to find all elements of an array that match a particular
pattern. So far, I used:
grep { /\t$var\t/ } @array
but it doesn't match. I have the impression, it tries to match only the
element of the array which are *exactly* matching. But I want a match
anywhere in any element of the array.
Here:
http://perldoc.perl.org/functions/grep.html
there is a "!" before the "/". What does this means? I didn't find
anything about this...
I also tried /.*\t$var\t.*/ but it doesn't match either...
Greetings,
------------------------------
Date: 27 Jun 2006 16:26:01 GMT
From: xhoster@gmail.com
Subject: Re: Searching each element of an array with grep
Message-Id: <20060627122624.114$ao@newsreader.com>
"KaZ" <kaz219@gawab.com> wrote:
> Hello,
>
> I'm trying to find all elements of an array that match a particular
> pattern. So far, I used:
>
> grep { /\t$var\t/ } @array
>
> but it doesn't match.
Of course it doesn't. @array is empty. But then again, even if the regex
did match, how would you know? The grep is in a void context.
> Here:
> http://perldoc.perl.org/functions/grep.html
> there is a "!" before the "/". What does this means? I didn't find
> anything about this...
It is an ordinary unary logical negation. See perldoc perlop.
Xho
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------------------------------
Date: Tue, 27 Jun 2006 18:26:01 +0200
From: "Dr.Ruud" <rvtol+news@isolution.nl>
Subject: Re: Searching each element of an array with grep
Message-Id: <e7rtjp.js.1@news.isolution.nl>
KaZ schreef:
> I'm trying to find all elements of an array that match a particular
> pattern. So far, I used:
>
> grep { /\t$var\t/ } @array
ITYM: grep /\t$var\t/, @array
Do these array-elements have <tab><some-text><tab> inside?
Variants:
grep /$var/, @array
grep /\s$var\s/, @array
grep /\b$var\b/, @array
--
Affijn, Ruud
"Gewoon is een tijger."
------------------------------
Date: Tue, 27 Jun 2006 10:00:16 -0700
From: Jim Gibson <jgibson@mail.arc.nasa.gov>
Subject: Re: Searching each element of an array with grep
Message-Id: <270620061000163044%jgibson@mail.arc.nasa.gov>
In article <1151424538.934504.212860@i40g2000cwc.googlegroups.com>, KaZ
<kaz219@gawab.com> wrote:
> Hello,
>
> I'm trying to find all elements of an array that match a particular
> pattern. So far, I used:
>
> grep { /\t$var\t/ } @array
>
> but it doesn't match. I have the impression, it tries to match only the
> element of the array which are *exactly* matching. But I want a match
> anywhere in any element of the array.
A regular expression either matches or doesn't match. We would need to
see the contents of $var and @array to tell you why any particular
element of @array either matches or doesn't.
If you want 'exact' matches between $var and any element of @array, you
can use the RE /^\Q$var$/, where \Q will quote any meta-characters in
$var. You can also use the more efficient 'eq' operator:
@matches = grep { $_ eq $var } @array;
If you want to get more help, please adhere to the guidelines for this
group and post a short, complete, working program that illustrates the
problems you are having. Thanks.
>
> Here:
> http://perldoc.perl.org/functions/grep.html
> there is a "!" before the "/". What does this means? I didn't find
> anything about this...
The ! here is the logical negation operator. The example is trying to
weed out comments:
@foo = grep { !/^#/ } @bar;
The regular expression /^#/ returns true for any line whose first
character is #. The ! flips that value to false, so that any line whose
first character is # is not included in the scalar list returned by
grep. Lines whose first character is NOT # end up in @foo.
>
> I also tried /.*\t$var\t.*/ but it doesn't match either...
There is no difference between /\t$var\t/ and /.*\t$var\t.*/ (except
for possible side effects). They will both match or both not match a
given string. .* at the beginning or end of a string is superfluous.
------------------------------
Date: Tue, 27 Jun 2006 17:06:27 GMT
From: "A. Sinan Unur" <1usa@llenroc.ude.invalid>
Subject: Re: Searching each element of an array with grep
Message-Id: <Xns97EF856EE3E99asu1cornelledu@127.0.0.1>
"Dr.Ruud" <rvtol+news@isolution.nl> wrote in news:e7rtjp.js.1
@news.isolution.nl:
> KaZ schreef:
>
>> I'm trying to find all elements of an array that match a particular
>> pattern. So far, I used:
>>
>> grep { /\t$var\t/ } @array
>
> ITYM: grep /\t$var\t/, @array
C:\DOCUME~1\asu1\LOCALS~1\Temp> perldoc -f grep
grep BLOCK LIST
grep EXPR,LIST
Why do you prefer the second the first form?
> grep /$var/, @array
>
> grep /\s$var\s/, @array
>
> grep /\b$var\b/, @array
Since you don't assign the results of grep to anything, they will be
lost.
Sinan
--
A. Sinan Unur <1usa@llenroc.ude.invalid>
(remove .invalid and reverse each component for email address)
comp.lang.perl.misc guidelines on the WWW:
http://augustmail.com/~tadmc/clpmisc/clpmisc_guidelines.html
------------------------------
Date: 27 Jun 2006 10:08:34 -0700
From: "KaZ" <kaz219@gawab.com>
Subject: Re: Searching each element of an array with grep
Message-Id: <1151428114.174680.148590@j72g2000cwa.googlegroups.com>
Thanks for your help.
I didn't wrote the whole command line, since for me the problem was in
the regex. But I found the solution, it had nothing to do with the
regex.
Sorry for the stupid question about the "!", I don't know how I missed
that.
------------------------------
Date: Tue, 27 Jun 2006 19:49:28 +0200
From: "Dr.Ruud" <rvtol+news@isolution.nl>
Subject: Re: Searching each element of an array with grep
Message-Id: <e7s27g.vs.1@news.isolution.nl>
A. Sinan Unur schreef:
> Dr.Ruud:
>> KaZ:
>>> I'm trying to find all elements of an array that match a particular
>>> pattern. So far, I used:
>>>
>>> grep { /\t$var\t/ } @array
>>
>> ITYM: grep /\t$var\t/, @array
>
> C:\DOCUME~1\asu1\LOCALS~1\Temp> perldoc -f grep
> grep BLOCK LIST
> grep EXPR,LIST
>
> Why do you prefer the second the first form?
Because the block isn't necessary. Because /\t$var\t/ is an expression.
>> grep /$var/, @array
>>
>> grep /\s$var\s/, @array
>>
>> grep /\b$var\b/, @array
>
> Since you don't assign the results of grep to anything, they will be
> lost.
As (I assumed that) the OP meant, I didn't care about the surroundings
like (for example) "@newarray = " and " ;".
The same format of question is:
<example>
I'm trying to find the first character at the end of a string that has a
particular value. So far, I used:
index $str, "\t", -4
but it tends to find an earlier "\t".
</example>
--
Affijn, Ruud
"Gewoon is een tijger."
------------------------------
Date: Tue, 27 Jun 2006 13:55:56 -0400
From: Ted Zlatanov <tzz@lifelogs.com>
Subject: Re: Test loop
Message-Id: <g69u0668our.fsf@CN1374059D0130.kendall.corp.akamai.com>
On 26 Jun 2006, kaz219@gawab.com wrote:
> I'm trying to do the following:
> for each value of an array, make a test.
> If the loop comes to the end without that the test became true a single
> time, do action A. Otherwise, just go on, without doing action A.
my $successful_test = 0;
foreach my $value (@values)
{
$successful_test ||= run_test($value);
}
runActionA() unless $successful_test;
Various grep/map solutions are possible but this is probably easiest
to understand.
Ted
------------------------------
Date: 6 Apr 2001 21:33:47 GMT (Last modified)
From: Perl-Users-Request@ruby.oce.orst.edu (Perl-Users-Digest Admin)
Subject: Digest Administrivia (Last modified: 6 Apr 01)
Message-Id: <null>
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End of Perl-Users Digest V10 Issue 9392
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