Need help with Regex

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

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Re: Need help with Regex by toolic (Bishop) on Nov 11, 2008 at 17:15 UTC
I'm not entirely sure what you want for output because you did not show an example. But, if you just want to grab the 6th column from your input, you could use split instead of a regex: use strict; use warnings; while (<DATA>) { my $num = (split)[5]; print "$num\n"; } __DATA__ > 4.23.88.0/23 64.135.0.1 0 1000 234 +46164 i > 4.23.89.0/24 64.135.0.1 0 1000 2014 +8 46164 i > 4.23.92.0/23 64.135.0.1 0 1000 2013 +8 46164 i > 4.23.92.0/22 64.135.0.1 0 1000 3018 + 46164 i > 4.23.94.0/23 64.135.0.1 0 1000 4041 +8 46164 i > 4.23.112.0/24 64.135.0.1 0 1000 1018 + 174 21889 i > 4.23.113.0/24 64.135.0.1 0 1000 2018 + 174 21889 i > 4.23.114.0/24 64.135.0.1 0 1000 18 1 +74 21889 i *> 4.36.118.0/24 64.135.0.1 0 1000 7018 + 174 21889 i [download] prints: `234 20148 20138 3018 40418 1018 2018 18 7018` [download]	[reply] [d/l] [select]
Re^2: Need help with Regex by ewhitt (Scribe) on Nov 13, 2008 at 09:10 UTC
Interesting. I have never seen "split" used like that before. How could I pass it a variable? Say I wanted to print "four" ? `$output = "one two three four five"; $output = (split $line)[4];` [download] Thanks!	[reply] [d/l]
Re^3: Need help with Regex by toolic (Bishop) on Nov 13, 2008 at 14:24 UTC
The parentheses around split forces it to return an array. The square brackets are used to select a single element from the array returned by split. We could either use a constant numeric value, such as 3, or we could use a scalar variable, such as `$col` to select the array item. Keep in mind that Perl arrays start at 0, not 1. So, "one" becomes array element `[0]`, and "four" is element `[3]`: `use strict; use warnings; my $col = 3; my $str = "one two three four five"; my $output = (split /\s+/, $str)[$col]; print "output=$output\n"; __END__ output=four` [download]	[reply] [d/l] [select]
Re: Need help with Regex by swampyankee (Parson) on Nov 11, 2008 at 17:58 UTC
&ellip;and if toolic's suggestion won't always work, i.e., the number of columns changes, you could try something like this: #/usr/bin/perl use strict; use warnings; while(<DATA>){ (my $junk, my $keep) = split(/\s1000\s/, $line, 2); my @datum = split(/\s+/,$keep); print shift(@datum),"\n"; } __DATA__ > 4.23.88.0/23 64.135.0.1 0 1000 234 +46164 i > 4.23.89.0/24 64.135.0.1 0 1000 2014 +8 46164 i > 4.23.92.0/23 64.135.0.1 0 1000 2013 +8 46164 i > 4.23.92.0/22 64.135.0.1 0 1000 3018 + 46164 i > 4.23.94.0/23 64.135.0.1 0 1000 4041 +8 46164 i > 4.23.112.0/24 64.135.0.1 0 1000 1018 + 174 21889 i > 4.23.113.0/24 64.135.0.1 0 1000 2018 + 174 21889 i > 4.23.114.0/24 64.135.0.1 0 1000 18 1 +74 21889 i *> 4.36.118.0/24 64.135.0.1 0 1000 7018 + 174 21889 i [download] I know that the second split and the print can be wrapped into one statement. I'm at work, so I don't want to spend too much time on this. Information about American English usage here and here. Floating point issues? Please read this before posting. — emc	[reply] [d/l]
Re: Need help with Regex by JavaFan (Canon) on Nov 11, 2008 at 19:27 UTC
`print $1 if /1000\s+([0-9]+)/;` [download] Be careful, it might grab an unintended number if there's another 1000 preceeding the 1000 you intend. But the regexp above grabs the "number after '1000'".	[reply] [d/l]
Re: Need help with Regex by Grey Fox (Chaplain) on Nov 11, 2008 at 17:46 UTC
Like I've said in previous posts there's lots of good regex info if you search around Perl Monks try Perlmonks Tutorial: Regular Expressions Tutorial, the Basics (for BEGINNERS) It helps if you try to code something up yourself then post. I've found learning by doing is the best way to get familiar with REGEX. I have also found http://www.regular-expressions.info/quickstart.html very helpful working with regex's. Lots of good examples. I found tools like http://www.txt2re.com/ or Eclipses regex tool to be helpful in debugging my regex commands. Good Luck. -- Grey Fox "We are grey. We stand between the darkness and the light" B5	[reply]


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