Regex MATCH

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

Hi i have written a regex to match some tags ..the issue is when i try to match "-"(HYPHEN) in the tag , "_"(UNDERSCORE) is also getting matched...the regex is written below:-

$Prefix='DOC_';
if ($line =~ /$Prefix[a-zA-Z]*[0-9]*-*[0-9a-z]{3}/)
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the tags are

DOC_001_123

DOC_002_214

DOC_001-548

DOC_001-987

I want the last two tags with the - but im getting every tags... where is the issue in the above regex..thanks....

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Re: Regex MATCH by kcott (Archbishop) on Sep 14, 2012 at 08:37 UTC
G'day stallion, Your problem is that `` matches zero* or more times. For `DOC_001_123`: `$Prefix` matches `DOC_` `[a-zA-Z]` matches zero times `[0-9]` matches zero times `-` matches zero times `[0-9a-z]{3}` matches `001` no further matching in regexp: `/$Prefix[a-zA-Z][0-9]-[0-9a-z]{3}/` successfully matches `DOC_001_123` That may be enough for you to fix your code. If not, please post a more representative sample of your tags: given the `[a-zA-Z]*` in your regexp, I assume some tags are more complicated than those posted here. -- Ken	[reply] [d/l] [select]
Re: Regex MATCH by 2teez (Vicar) on Sep 14, 2012 at 08:44 UTC
hi, If I understand your question, you want to match the line that has HYPHEN towards end of the lines. If so, the below script does that `use warnings; use strict; while ( defined( my $line = <DATA> ) ) { chomp $line; print $line, $/ if $line =~ m/\-[0-9a-z]{3}/; } __DATA__ DOC_001_123 DOC_002_214 DOC_001-548 DOC_001-987` [download] Output `DOC_001-548 DOC_001-987` [download] UPDATE: You really can see, how your Regex matches, using `use re 'debug';` [download] in your script or you can get explanation of a regular expression using YAPE::Regex::Explain If you tell me, I'll forget. If you show me, I'll remember. if you involve me, I'll understand. --- Author unknown to me	[reply] [d/l] [select]
Re: Regex MATCH by Utilitarian (Vicar) on Sep 14, 2012 at 08:14 UTC
With the tags you provide, wouldn't something like the following be more discerning? `Utilitarian@busybox ~$cat tmp/tmp.pl #!/usr/bin/perl use strict; use warnings; my $prefix='DOC_'; for (<DATA>){ chomp(my $line=$_); print "$line\n" if ($line =~ /^$prefix[0-9]{3}(_\|-)[0-9]{3}$/); } __DATA__ DOC_001_123 DOC_002_214 DOC_001-548 DOC_001-987 Utilitarian@busybox ~$perl tmp/tmp.pl DOC_001_123 DOC_002_214 DOC_001-548` [download] EDIT bart below is correct, to constrain the matches to hyphens the regex above should have read `/^$prefix[0-9]{3}-[0-9]{3}$/` `print "Good ",qw(night morning afternoon evening)[(localtime)[2]/6]," fellow monks."`	[reply] [d/l] [select]
Re^2: Regex MATCH by bart (Canon) on Sep 14, 2012 at 10:45 UTC
You've got it backwards. His regex matches, but he doesn't want it to match.	[reply]
Re: Regex MATCH by BillKSmith (Monsignor) on Sep 14, 2012 at 14:31 UTC
Others have already pointed out the problem with the asterics in your regex. I suspect that you intend to match the middle field if it contains no digits (letters only) or no letters (digits only - the case in all your examples) as well letters followed by digits, but not if the field is empty. I assume that the asterick after the hyphen is a mistake. You probablly intend to require only one hyphen as a field seperator. Here is an implementation of my assumptions. `use strict; use warnings; use Readonly; Readonly::Scalar my $PREFIX => qr/DOC_/; Readonly::Scalar my $FILTER => qr/ $PREFIX (?: [A-Za-z]+\d* \| [A-Za-z]*\d+ ) - [0-9a-z]{3} /x; my @tags = qw( DOC_001_123 DOC_002_214 DOC_001-548 DOC_001-987 ); my @dash_tags = grep {/$FILTER/} @tags; print "@dash_tags\n";` [download] Bill	[reply] [d/l]