in reply to Re: Regex help
in thread Regex help

Its not HW its for my job, im trying to parse data outputed from a sel2030. Ive never used regexs before and I am having a hard time figuring out read down a list and to get the parser to start at correct place in the list. Is there anyway besides using split? I am passing these regex expressions into xml attributes so if there is a way to do it without using perl commands that would be optimal. Any ideas great Monks?

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Re^3: Regex help
by kennethk (Abbot) on Jun 21, 2012 at 14:34 UTC
    There are number of ways to do it with straight regular expressions, but the technology you are feeding this into (and thus the necessary input-output mapping) is unfamiliar to me. Parsing one of your lines may be as easy as /^\s*(\S+)\s+(\S+)\s*$/, but maybe this needs the m modifier depending on context. This particular expression will fail on all lines other than your data lines, since all it does is (thanks to YAPE::Regex::Explain): 
    The regular expression:

(?m-isx:^\s*(\S+)\s+(\S+)\s*$)

matches as follows:
  
NODE                     EXPLANATION
----------------------------------------------------------------------
(?m-isx:                 group, but do not capture (with ^ and $
                         matching start and end of line) (case-
                         sensitive) (with . not matching \n)
                         (matching whitespace and # normally):
----------------------------------------------------------------------
  ^                        the beginning of a "line"
----------------------------------------------------------------------
  \s*                      whitespace (\n, \r, \t, \f, and " ") (0 or
                           more times (matching the most amount
                           possible))
----------------------------------------------------------------------
  (                        group and capture to \1:
----------------------------------------------------------------------
    \S+                      non-whitespace (all but \n, \r, \t, \f,
                             and " ") (1 or more times (matching the
                             most amount possible))
----------------------------------------------------------------------
  )                        end of \1
----------------------------------------------------------------------
  \s+                      whitespace (\n, \r, \t, \f, and " ") (1 or
                           more times (matching the most amount
                           possible))
----------------------------------------------------------------------
  (                        group and capture to \2:
----------------------------------------------------------------------
    \S+                      non-whitespace (all but \n, \r, \t, \f,
                             and " ") (1 or more times (matching the
                             most amount possible))
----------------------------------------------------------------------
  )                        end of \2
----------------------------------------------------------------------
  \s*                      whitespace (\n, \r, \t, \f, and " ") (0 or
                           more times (matching the most amount
                           possible))
----------------------------------------------------------------------
  $                        before an optional \n, and the end of a
                           "line"
----------------------------------------------------------------------
)                        end of grouping
----------------------------------------------------------------------

    [download]
    and can be shown to work on this example with 
    #!/usr/bin/perl -w
use strict;
use Data::Dumper;

$_ = <<'EOT';
Port 1 Database Assignments

  Region    Data Type   # Records

  GLOBAL    --
  LOCAL     --
  BUF       --
  D1        Unused
  D2        Unused
  D3        Unused
  D4        Unused
  D5        Unused
  D6        Unused
  D7        Unused
  D8        Unused
  A1        Unused
  A2        Unused
  A3        Unused
  USER      Unused
EOT

my %hash;
while (/^\s*(\S+)\s+(\S+)\s*$/mg) {
   $hash{$1} = $2;
}
print Dumper \%hash;

    [download]
    However, it'll break pretty quickly if your input is not representative; e.g. if you Region or Data Type contain white space (this looks fixed width to me) or if # Records is not null.

    #11929 First ask yourself `How would I do this without a computer?' Then have the computer do it the same way.

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      Thanks this was really helpful, you pretty much did all the work for me. I am trying to understand your regex expression which will take a bit. One more questions, is there no way to record the "# Record" column cells as being blank?
[reply]

        Recording the "# Record" column cells as being blank is easy; the hard part would be changing the expression to record non-blank entries. You could just add an empty pair of parentheses, a la /^\s*(\S+)\s+(\S+)\s*()$/. Given that none of the lines contain three non-space blocks, you might even say /^\s*(\S+)\s+(\S+)\s*(\S*)\s*$/. Keep in mind that given these are such general expressions, it is absolutely essential that you test this against real input and be skeptical of the results.

        #11929 First ask yourself `How would I do this without a computer?' Then have the computer do it the same way.

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