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Help nawk change external variable

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# 1  
Old 07-14-2011
Help nawk change external variable
Hello,

I have external variable rownumber, I am processing files within a loop and I would like to keep incrementing rownumber. What is happening is inside nawk section it passes rownumber but it never gets updated. I want to update rownumber inside the nawk, I would appreciate your help

Code:
rownumber=0
for FILE in $FILELIST
do
    filename=`basename $FILE`
    curvename=`echo $filename | awk '{FS="."}{print $1}'`
    rundate=`echo $filename | awk '{FS="."}{print $2}'`
    echo $curvename
    nawk '
    FNR==1 {
        numheadrecords = $1;
        rowstoprocess  = numheadrecords + 2;
        next;
    }
    FNR<rowstoprocess {
        RCount = RCount + 1;
        julianmdate = $1;
        rate        = $3;
        mdate      = $4
        printf "%s,%s,%s,%s,%s,%s\n", LowFile, RDate, mdate, julianmdate, rate, RCount;
    }
    ' LowFile=$curvename RDate=$rundate RCount=$rownumber $FILE >>$OUTPUTFILE
done

Last edited by srattani; 07-14-2011 at 03:06 PM..
# 2  
Old 07-14-2011
awk doesn't have access to shell variables, you'll have to store it somewhere.

Code:
 awk '

...

END {        print RCount > "/dev/stderr" }' filename >> outname 2> varfile
VAR=`cat varfile`

You could also just do everything inside awk, and wouldn't need to worry about getting variables into and out of it.
# 3  
Old 07-14-2011
Hi,

Thanks for your reply. In my case If you see I do not have an END, so when would I know that nwak is done processing the rows and I should store RCount in a file.

I am assuming initially I will have to store RCount as 0 in varfile. Inside nwak I have to read it from file keep incrementing and thne once done I write it out to the file?

Please advise how should I accomplish it, I am new to Unix scripting so I would really appreciate your help.
# 4  
Old 07-14-2011
Quote:
Originally Posted by srattani
Hi,

Thanks for your reply. In my case If you see I do not have an END, so when would I know that nwak is done processing the rows and I should store RCount in a file.
That's okay, just add the END { } block after the other blocks. It should start on its own line, just like all the other blocks you have in that awk statement. END is a special block that gets run when awk runs out of input.
Quote:
I am assuming initially I will have to store RCount as 0 in varfile.
Nope, you don't. Just do what I showed you.
Quote:
Inside nwak I have to read it from file keep incrementing and thne once done I write it out to the file?
Nope, you don't, just do what I showed you.

Sequence of events is:
  1. Shell variable copied into awk
  2. awk finishes processing data, calls END {} block, prints new value into stderr, which is saved to varfile.
  3. awk quits.
  4. shell reads varfile back into the variable.

Awk and the shell are separate so awk can't affect each others' variables. So awk just prints the variable into a file when its done for the shell to read and update itself with.
Last edited by Corona688; 07-14-2011 at 04:18 PM..
# 5  
Old 07-14-2011
Hi,

I still dont exactly follow. Will it be something like follows?

Code:
nawk '
    FNR==1 {
        numheadrecords = $1;
        rowstoprocess  = numheadrecords + 2;
        next;
    }
    FNR<rowstoprocess {
        RCount = RCount + 1;
        julianmdate = $1;
        rate        = $3;
        mdate      = $4
        printf "%s,%s,%s,%s,%s,%s\n", LowFile, RDate, mdate, julianmdate, rate, RCount;
    }
    END { print RCount > "/dev/stderr" }' filename >> outname 2> varfile
VAR=`cat varfile`}
    ' LowFile=$curvename RDate=$rundate RCount=$rownumber $FILE >>$OUTPUTFILE

# 6  
Old 07-14-2011
You're taking my example way too literally. "filename >> outname 2> varfile" was outside the awk statement I showed you and certainly shouldn't be inside yours. (The > "/dev/null" belongs inside, though.)

The VAR=`cat varfile` is not part of the awk statement, it happens after. It reads varfile into VAR inside the shell, getting back the value awk saved when it quit. I don't know how you ended up with the } after it. Again it's not meant to be taken literally -- you wanted rowcount, not VAR.

Come to think of it a faster way to do it is read rownumber <varfile

So:

Code:
rownumber=0
for FILE in $FILELIST
do
    filename=`basename $FILE`
    curvename=`echo $filename | awk '{FS="."}{print $1}'`
    rundate=`echo $filename | awk '{FS="."}{print $2}'`
    echo $curvename
    nawk '
    FNR==1 {
        numheadrecords = $1;
        rowstoprocess  = numheadrecords + 2;
        next;
    }
    FNR<rowstoprocess {
        RCount = RCount + 1;
        julianmdate = $1;
        rate        = $3;
        mdate      = $4
        printf "%s,%s,%s,%s,%s,%s\n", LowFile, RDate, mdate, julianmdate, rate, RCount;
    }
    END { print RCount > "/dev/stderr" }
    ' LowFile=$curvename RDate=$rundate RCount=$rownumber $FILE >>$OUTPUTFILE 2> varfile
    read rowcount <varfile
done

# delete temporary file when you're done
rm -f varfile

This User Gave Thanks to Corona688 For This Post:
srattani
# 7  
Old 07-14-2011
Thank you very much, worked like a charm. Appreciate all your patience and help.
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