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Full Discussion: Just need some guidance on this nawk
Top Forums UNIX for Dummies Questions & Answers Just need some guidance on this nawk Post 302827485 by newbie_01 on Friday 28th of June 2013 09:04:42 PM
Old 06-28-2013
Just need some guidance on this nawk
Hi,

I am trying to debug some KSH script and it has the nawk portion below. I just want to confirm whether I understand what it does correctly.

Example usage of the nawk line is run as below:

Code:
 
nawk '/^#/ {next}
$1~/^'testp.cfg'$|^'testp.cfg'\.testdb\.com\.ph$/ {
   c=0
   while (getline) {
     gsub (" ","")
     s=tolower($0)
     if (s~/host=/) {
        sub("^.*host=","",s)
        sub("\\\).*","",s)
        print s
        exit
     }
     c++
     if (c>20) {exit}
   }
}' $TNSNAMES

$TNSNAMES is a tnsnames.ora file, excerpts of some of its lines as below:

Code:
 
testd.testdb.com.ph = 
  (DESCRIPTION = 
        (ADDRESS = 
          (COMMUNITY = tcpip.world)
          (PROTOCOL = TCP)
          (Host = testd.testdb.com.ph)
          (Port = 25036)
        )
      (CONNECT_DATA = 
        (SID = testd)
           (GLOBAL_NAME = testd.testdb.com.ph)
      )
  )
testp.cfg = 
  (DESCRIPTION = 
        (ADDRESS = 
          (COMMUNITY = tcpip.world)
          (PROTOCOL = TCP)
          (Host = testp1)
          (Port = 5000)
        )
      (CONNECT_DATA = 
        (SID = testp)
           (GLOBAL_NAME = testp.cfg)
      )
  )

From what I understand, the nawk excludes all lines that begins with a # and if it finds a line that begins with testp.cfg or testp.cfg.testdb.com.ph, and starting from that line, it reads a line, strips the spaces, and convert it to lower case. Now I don't understand what this section of the nawk does?


Code:
     if (s~/host=/) {
        sub("^.*host=","",s)
        sub("\\\).*","",s)
        print s
        exit
     }
     c++
     if (c>20) {exit}


Does the first sub strips all spaces before the host= string? But what does the second sub do? Remove everything from the first dot (.)?

Is the c variable means it will only process 20 lines from when it find the testp.cfg or testp.cfg.testdb.com.ph string?

Any feedback much appreciated. Thanks in advance.
 

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LEARN ABOUT MOJAVE

ucblinks

ucblinks(1B)                                         SunOS/BSD Compatibility Package Commands                                         ucblinks(1B)

NAME

       ucblinks - adds /dev entries to give SunOS 4.x compatible names to SunOS 5.x devices

SYNOPSIS

       /usr/ucb/ucblinks [-e rulebase] [-r rootdir]

DESCRIPTION

       ucblinks  creates symbolic links under the /dev directory for devices whose SunOS 5.x names differ from their SunOS 4.x names. Where possi-
       ble, these symbolic links point to the device's SunOS 5.x name rather than to the actual /devices entry.

       ucblinks does not remove unneeded compatibility links; these must be removed by hand.

       ucblinks should be called each time the system is reconfiguration-booted, after any new SunOS 5.x links that are needed have been  created,
       since the reconfiguration may have resulted in more compatibility names being needed.

       In  releases prior to SunOS 5.4, ucblinks used a  nawk rule-base to construct the SunOS 4.x compatible names. ucblinks no longer uses  nawk
       for the default operation, although  nawk rule-bases can still be specifed with the -e option.  The  nawk rule-base equivalent to the SunOS
       5.4 default operation can be found in /usr/ucblib/ucblinks.awk.

OPTIONS

       -e rulebase     Specify rulebase as the file containing nawk(1) pattern-action statements.

       -r rootdir      Specify rootdir as the directory under which dev and devices will be found, rather than the standard root directory /.

FILES

       /usr/ucblib/ucblinks.awk        sample rule-base for compatibility links

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE         |      ATTRIBUTE VALUE        |
       +-----------------------------+-----------------------------+
       |Availability                 |SUNWscpu                     |
       +-----------------------------+-----------------------------+

SEE ALSO

       devlinks(1M), disks(1M), ports(1M), tapes(1M), attributes(5)

SunOS 5.10                                                          13 Apr 1994                                                       ucblinks(1B)
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