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

I am reading a file and need to find several matches within
a line, i have successfully managed the first match but
the second match is proving rather difficult.

$line1="12/123 11-abc 456 a 1/2 zyx this is the last"
$line2="14/456 11-abc 456 a 1/2 zyx this is it"

i want to match with 123 11 and extract '12/123 11-abc 456'
then proceed to check for 'zyx'and if it matches extract the remaining line

$line1 will result in a match on both counts and the variables are stored into 2 variables

$line 2 will not result in any match and i proceed to next line

Replies are listed 'Best First'.
Re: Extracting data after a match
by Enlil (Parson) on Jun 10, 2003 at 20:30 UTC
    one way to do it:
    while ( <DATA> ) {
  if ( /^(\d+\/123 11.*?)(?= a )(?:.*?zyx(.*))?/ ) {
    print "THIS IS THE FIRST MATCH: $1" ,$/;
    print "THIS IS THE SECOND MATCH: $2" ,$/ if defined $2;
  }

}

__DATA__
12/123 11-abc 456 a 1/2 zyx this is the last 1
13/123 11-abc 456 a 1/2 zyx this is the last 2
14/456 11-abc 456 a 1/2 zyx this is it
15/456 11-abc 456 a 1/2 zyx this is it
16/123 11-abc 456 a 1/2 zyx this is the last 3
17/123 11-abc 456 a 1/2 xyz this is the last 3

    [download]
    The regex is thus explained by YAPE::Regex::Explain:
    C:\>perl -MYAPE::Regex::Explain -e "print YAPE::Regex::Explain->new('^
+(\d+\/123 11.*?)(?= a )(?:.*?zyx(.*))?')->explain"
The regular expression:

(?-imsx:^(\d+\/123 11.*?)(?= a )(?:.*?zyx(.*))?)

matches as follows:

NODE                     EXPLANATION
----------------------------------------------------------------------
(?-imsx:                 group, but do not capture (case-sensitive)
                         (with ^ and $ matching normally) (with . not
                         matching \n) (matching whitespace and #
                         normally):
----------------------------------------------------------------------
  ^                        the beginning of the string
----------------------------------------------------------------------
  (                        group and capture to \1:
----------------------------------------------------------------------
    \d+                      digits (0-9) (1 or more times (matching
                             the most amount possible))
----------------------------------------------------------------------
    \/                       '/'
----------------------------------------------------------------------
    123 11                   '123 11'
----------------------------------------------------------------------
    .*?                      any character except \n (0 or more times
                             (matching the least amount possible))
----------------------------------------------------------------------
  )                        end of \1
----------------------------------------------------------------------
  (?=                      look ahead to see if there is:
----------------------------------------------------------------------
     a                       ' a '
----------------------------------------------------------------------
  )                        end of look-ahead
----------------------------------------------------------------------
  (?:                      group, but do not capture (optional
                           (matching the most amount possible)):
----------------------------------------------------------------------
    .*?                      any character except \n (0 or more times
                             (matching the least amount possible))
----------------------------------------------------------------------
    zyx                      'zyx'
----------------------------------------------------------------------
    (                        group and capture to \2:
----------------------------------------------------------------------
      .*                       any character except \n (0 or more
                               times (matching the most amount
                               possible))
----------------------------------------------------------------------
    )                        end of \2
----------------------------------------------------------------------
  )?                       end of grouping
----------------------------------------------------------------------
)                        end of grouping
----------------------------------------------------------------------

    [download]
    Though I think an easier approach might be just using an if construct like so:
    while ( <DATA> ) {
  if ( /^(\d+\/123 11.*?) a / ) { #first matched
    my $first = $1;
    my $second = $1 if /\G.*?zyx(.*)/; #check for next match
    print "First = $first\n";
    #print $second only if it is defined;
    print "Second = $second\n" if defined $second; 
  }

}

    [download]
    Dependent on what your data might actually look like, the regex's might need changing to better suit your needs.

    -enlil

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[d/l]
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Re: Extracting data after a match
by pzbagel (Chaplain) on Jun 10, 2003 at 20:04 UTC

    I don't know whether you want to catch the string before zyx, using the /g and \G may not be necessary if you don't care about it, although it would ensure that you get the right zyx. How about something like: 

    $line[0]="12/123 11-abc 456 a 1/2 zyx this is the last";
$line[1]="14/456 11-abc 456 a 1/2 zyx this is it";

for (@line)
{
        if(m|(\d+/123 11-[a-z]+ \d+)|g)
        {
                $start=$1;
                /\G(.*?) zyx (.*)$/;
                print "Start of record:$start\nBefore zyx:$1\nand Afte
+r zyx:$2\n";
        }
}

__OUTPUT__

Start of record:12/123 11-abc 456
Before zyx: a 1/2
and After zyx:this is the last

    [download]
[reply]
[d/l]

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