awk – Update Line Based on Previous Line

I have a issue since I'm not familiar with awk. I have csv file generated from sar -d output converted to csv style:

12:33:41        unix,restarts
12:35:00,lofi4096,0,0.0,0,0,0.0,0.0
,iscsi0,0,0.0,0,0,0.0,0.0
,scsi_vhc,0,0.0,0,0,0.0,0.0
,nfs1,0,0.0,0,0,0.0,0.0

12:45:00,lofi4096,0,0.0,0,0,0.0,0.0
,iscsi0,0,0.0,0,0,0.0,0.0
,scsi_vhc,0,0.0,0,0,0.0,0.0
,nfs1,0,0.0,0,0,0.0,0.0

and I want to convert to this

12:33:41        unix,restarts
12:35:00,lofi4096,0,0.0,0,0,0.0,0.0
12:35:00,iscsi0,0,0.0,0,0,0.0,0.0
12:35:00,scsi_vhc,0,0.0,0,0,0.0,0.0
12:35:00,nfs1,0,0.0,0,0,0.0,0.0

12:45:00,lofi4096,0,0.0,0,0,0.0,0.0
12:45:00,iscsi0,0,0.0,0,0,0.0,0.0
12:45:00,scsi_vhc,0,0.0,0,0,0.0,0.0
12:45:00,nfs1,0,0.0,0,0,0.0,0.0

My attempt but since awk reads line by line I don't know out to keep the previous line value. I would expect that what I have should work. Any idea how I can obtain my desired result. I tried with awk, but I guess this should be possible with sed or the hard way with a custom shell script ( I'm trying to avoid doing this part ).

#!/usr/bin/awk -f
BEGIN {
        FS=",";
}
{
        print $1
        if ($1 != "") {
                mydate=$1;
                print $0;
        }
        else {
                print $mydate","$0;
        }
}

Running the system with Solaris 11.1.

Best Answer

It gets a bit long as you seem to have blank lines in the input. The following might work for you:

awk -F'[, ]' '{if (NF!=0 && $1=="") {$1=prev} prev=$1}1' OFS=, inputfile

The idea is to split fields on , and whitespace (the latter in order to handle the first line of input). Check if the first field is blank and the number of fields is not zero (handle blank lines), then replace the first field with the previously stored first field.

For your input, it'd produce:

Best Answer

Related Solutions

Related Question