awk script: need help


 
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# 15  
Old 07-15-2016
Hi bhupeshchavan,
Here is a copy of RudiC's code with comments added.
Code:
# Note that this script reads the file a line at a time (not a record at a time
# with a line ontaining "eof" as the record terminator).  This will work with
# any standards-conforming version of awk; while the other code you're using
# with RS set to "eof\n" only works on versions of awk that support
# multi-character record separator values (which is not required by the
# standards).
awk '
/eof/   {# For each input line that contains the string "eof"...
	 #	if the HR saved for this group is <= 12, print this record.
	 if (HR <= 12)   print TMP

	 # Clear the hold area for the current record and reset the delmiter to
	 # an empty string.
         TMP = DL = ""

	 # Read the next input line and skip the remaining steps in this script
	 # for this line.
         next
        }
        {# For every line in the input file (other than the "eof" lines we have
	 # discarded), add the current delimter and the current input line to
	 # the saved text containing the current record and set the delimiter to
	 # be used when adding later lines to this record to a comma.
	 TMP = TMP DL $0
         DL  = ","
        }
/^time/ {# For lines that start with the string "time", save two characters
	 # starting with the sixth character on this line in the variable HR.
	 # (I.e. set HR to the two digit hour from the "time" line.)
	 HR = substr ($0, 6, 2)
        }
' log	# End the awk script and specify that the file named "log" is to be
	# read as input.

Does this clear up your confusion with RudiC's suggestion?

Again, note that this works fine as long as you're looking for times with an end-of-range greater than or equal to 10. If at some point in the future you might want to test for a range line 2am to 9am, you would need to be sure that you're performing numeric comparisons instead of string comparisons. If this becomes an issue for you, the easy way to do that with the above code is to change:
Code:
         HR = substr ($0, 6, 2)

to:
Code:
         HR = subset ($0, 6, 2) + 0


Last edited by Don Cragun; 07-15-2016 at 07:10 PM.. Reason: Fix typo: s/\$ st/# st/
These 2 Users Gave Thanks to Don Cragun For This Post:
# 16  
Old 07-16-2016
Hi Don,

Thank you very much for the explanation.

I got it , just for my understanding(like setting up values first and then evaluating it) i tried the below code and the output is fine, please check if this is the correct way to write or i should follow the RudiC's process of writing it.
Code:
awk '
/^time/ {HR = substr ($0, 6, 2)
        }
/eof/   {if (HR <= 12)   print TMP
         TMP = DL = ""
         next
        }
        {TMP = TMP DL $0
         DL  = ","
        }
' log

I believe that TMP keeps on adding the content to the TMP for the other lines until it finds eof. But when we use "TMP = TMP DL $0 DL=","", this is what i am still not sure about.
TMP=TMP means all the values till eof then why should we use DL and $0 after that .What does it mean to TMP.

Can we just TMP=TMP and set OFS="," at the beginning.I tried the below code but no output.
Code:
awk '
 BEGIN{OFS=","}
 /eof/   {if (HR <= 12)   print TMP
          TMP =""
          next
         }
         {TMP = TMP
         }
 /^time/ {HR = substr ($0, 6, 2)
         }
 ' log

Please help.

Thank you.
# 17  
Old 07-16-2016
awk works in a way that all pattern {action} pairs are being executed on the actual line until exhausted or otherwise terminated. Then the next line is read and the execution is repeated. So the sequence of operations doesn't matter as long as you don't want to influence the flow within a line. That's why the position of the time check is irrelevant. In awk, string concatenation is done by just listing the strings like str1 str2 str3, so TMP = TMP DL $0 assigns to TMP the old value of TMP plus DL plus the actual line. On the first occurrence, TMP and DL are empty strings, so the string starts with $0 only.
This User Gave Thanks to RudiC For This Post:
# 18  
Old 07-16-2016
Hi RudiC,
I seem to get the logic now.My understanding is below:

TMP = TMP DL $0
1st line TMP = "" "" name=admin --> since $0 is this value.
DL=","
2nd line TMP = name=admin,(comma because we have specified it to a comma in the earlier statemant) transid=01

TMP value now --> name=admin,transid=01

3rd line TMP= name=admin,transid=01, $0-->time=06.58.51 HR value is also set in this line

TMP value now --> name=admin,transid=01,time=06.58.51

4th line TMP --> name=admin,transid=01,time=06.58.51,message=test

then comes eof line where HR is evaluated and print TMP is executed.

Is this right.

Thanks.
# 19  
Old 07-16-2016
Hi bhupeshchavan,
Yes. You've got it.
This User Gave Thanks to Don Cragun For This Post:
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