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Full Discussion: nawk use
Top Forums UNIX for Advanced & Expert Users nawk use Post 302157375 by Perderabo on Thursday 10th of January 2008 07:34:27 PM
Old 01-10-2008
'c-->0;$0~s{if(b)for(c=b+1;c>1;c--)print r[(NR-c+1)%b];print;c=a}b{r[NR%b]=$0}'
has 3 pattern-action statements:
1) c-->0;
2) $0~s{if(b)for(c=b+1;c>1;c--)print r[(NR-c+1)%b];print;c=a}
3) b{r[NR%b]=$0}

The first one has no explicit action so the action is to simply print the entire record. But in this case the semicolon is needed so that it doesn't run in to the second staement. The second statement has an explicit action which is in braces and the braces are enough to separate it from the third. Now consider these statements in reverse order...

3) b{r[NR%b]=$0}
The pattern is b, which is asking if b is equal to zero. If b is non-zero we need to save records in case we need them later. But if b is zero, we can skip this since we do not want any "before" records displayed. If b is, say, 5, we will always have the last 5 records in the r array.

2) $0~s{if(b)for(c=b+1;c>1;c--)print r[(NR-c+1)%b];print;c=a}
The pattern $0~s simply asks if the record matches the search criteria we stored in s. If so and if b is non-zero, we print those records that we saved in step 3 above. Then we print the current record. Then c=a sets up the next step to be explained...

1) c-->0;
c gets set to a (number of "after" records) when we find a match. The c-- part decrements c after we use it. And we use it to see if it is greater than zero. This is how the "after" records are printed.
Last edited by Perderabo; 01-17-2008 at 08:34 AM.. Reason: fix some typos
 

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LEARN ABOUT DEBIAN

getds

GETDS(1p)						User Contributed Perl Documentation						 GETDS(1p)

NAME

       getds - Create a DS record from DNSKEYing information

SYNOPSIS

	 getds <domain>

DESCRIPTION

       getds will create a DS record from DNSKEYs for the specified DNS domain.  It does this by converting DNSKEYs to DS records using the
       specified hashing algorithm.  The results can then be passed to upstream DNSSEC-supporting parents or to DLV registries.

       getds will also pull the parent's published DS records and compare them against the existing keys.  It will then list any DS records not
       published in the parent, as well as any DS records that are published in the parent but which don't match an existing key.

OPTIONS

       getds takes the following options:

       -a ALGORITHMS
       --hash-algorithm algorithm ALGORITHMS
	   This option specifies the hash algorithm to use when converting DNSKEYs to DS records.  It may be a comma-separated list if multiple
	   algorithms are desired.  The algorithms to choose from may be either SHA256 or SHA1.

	   The default is SHA256,SHA1

       -z
       --print-zsks
	   This option causes getds to print ZSK DS records, as well as KSK records.

       -p
       --dont-check-parent
	   Instructs getds to not check the records in the parent for their published DS records.

       -q
       --quiet
	   Produces quiet output with no explanatory headers.  In other words, it only prints the DS records generated from the DNSKEYs.

	   Note: Running with -q implies -p.

SECURITY CONSIDERATIONS

       By default, getds pulls data from the live DNS.	If your DNS resolver isn't configured so that this is pulled securely, then the results
       can't be trusted.

COPYRIGHT

       Copyright 2008-2012 SPARTA, Inc.  All rights reserved.  See the COPYING file included with the DNSSEC-Tools package for details.

AUTHOR

       Wes Hardaker, hardaker AT AT AT users.sourceforge.net

perl v5.14.2							    2012-06-21								 GETDS(1p)
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