How do I write an output from bash script to the second line of the CSV file that contains headers? - bash

Question

I have a bash script that writes its output to the beginning of a CSV file. I need it to maintain the headers on the first line. I tried to use awk and sed but didn't succeed.
I got the main script which is used to make a SSH connection:
for n in $(cat list.txt)
do
ssh -t root#$n /etc/m_chkdsk_app.sh
done
list.txt contains servers names
server1
server2
server3
server4
and the run the following script on the remote computers
if [ -f /lnxfiler/diskstatus/m_chkdsk.csv ]
then
printf "$(cat /proc/sys/kernel/hostname)" >> /lnxfiler/diskstatus/New_m_chkdsk.csv && printf "," >> /lnxfiler/diskstatus/New_m_chkdsk.csv && printf "$(date +%d-%m-%Y)" >> /lnxfiler/diskstatus/New_m_chkdsk.csv && df -h | grep /dev/mapper/rootvg-var | awk '{printf "," $2 "," $3 "," $5 "," $6 "\n"}' >> /lnxfiler/diskstatus/New_m_chkdsk.csv
printf "$(cat /proc/sys/kernel/hostname)" >> /lnxfiler/diskstatus/New_m_chkdsk.csv && printf "," >> /lnxfiler/diskstatus/New_m_chkdsk.csv && printf "$(date +%d-%m-%Y)" >> /lnxfiler/diskstatus/New_m_chkdsk.csv && df -h | grep "/dev/mapper/rootvg-sap " | awk '{printf "," $2 "," $3 "," $5 "," $6 "\n"}' >> /lnxfiler/diskstatus/New_m_chkdsk.csv
cat /lnxfiler/diskstatus/m_chkdsk.csv >> /lnxfiler/diskstatus/New_m_chkdsk.csv
mv /lnxfiler/diskstatus/New_m_chkdsk.csv /lnxfiler/diskstatus/m_chkdsk.csv
else
printf "$(cat /proc/sys/kernel/hostname)" >> /lnxfiler/diskstatus/m_chkdsk.csv && printf "," >> /lnxfiler/diskstatus/m_chkdsk.csv && printf "$(date +%d-%m-%Y)" >> /lnxfiler/diskstatus/m_chkdsk.csv && df -h | grep /dev/mapper/rootvg-var | awk '{printf "," $2 "," $3 "," $5 "," $6 "\n"}' >> /lnxfiler/diskstatus/m_chkdsk.csv
printf "$(cat /proc/sys/kernel/hostname)" >> /lnxfiler/diskstatus/m_chkdsk.csv && printf "," >> /lnxfiler/diskstatus/m_chkdsk.csv && printf "$(date +%d-%m-%Y)" >> /lnxfiler/diskstatus/m_chkdsk.csv && df -h | grep "/dev/mapper/rootvg-sap " | awk '{printf "," $2 "," $3 "," $5 "," $6 "\n"}' >> /lnxfiler/diskstatus/m_chkdsk.csv
fi
exit
When I run the main script, I need all the output of the script to be added after the header.
Server Name,Date,Disk Size,Used,Use%,Mounted on
server1,08-09-2020,2.0G,363M,20%,/var
server1,08-09-2020,15G,41M,1%,/usr/sap
server1,08-09-2020,200G,237M,1%,/suse_manager
server2,08-09-2020,2.0G,138M,8%,/var
server2,08-09-2020,20G,6.6G,36%,/srv
server2,08-09-2020,80G,6.7G,9%,/srv/NFS
server3,08-09-2020,2.0G,363M,20%,/var
server3,08-09-2020,15G,41M,1%,/usr/sap
server4,08-09-2020,2.0G,138M,8%,/var
server4,08-09-2020,20G,6.6G,36%,/srv
server4,08-09-2020,80G,6.7G,9%,/srv/NFS

Answer 1

Here's a quick refactoring.
Driver script; don't read lines with for:
head -n 1 result.csv >newresult.csv
while IFS= read -r host; do
do
ssh -t "root#$host" /etc/m_chkdsk_app.sh </dev/null
done < list.txt >>newresult.csv
mv newresult.csv result.csv
Remote script:
df -h /dev/mapper/rootvg-var /dev/mapper/rootvg-sap |
awk -v date=$(date +%d-%m-%Y) 'BEGIN { OFS="," }
NR==FNR { host=$0; next }
/\/dev/ { print host, date, $2, $3, $5, $6 }
' /proc/sys/kernel/hostname - |
tee /lnxfiler/diskstatus/m_chkdsk.csv
The original script had tremendous amounts of repetition but it's of course possible that I have overlooked some crucial difference between almost identical code snippets. That's actually one of the reasons to avoid repeating yourself.
Selectively overwriting the old results on the remote server in slightly different fashion depending on whether the file already exists seemed entirely superfluous, so I took that out.
This assumes that you have old results in result.csv and that the first header line is so incredibly hard to get right that you have to copy it from the old file. It would probably be easier to just hard-code the script to write a new first line.
Depending on how robust you need this to be, maybe actually add set -e to the start of both scripts. If you don't absolutely have to store the results on the remote disk as well, that would cut out one of the main failure scenarios, and simpli|y the script still more.

Answer 2

If you have a file1.csv with data already in it, you can write all your new data to a tempfile.csv and then import it with an easy sed -
sed -i '1rtempfile.csv' file1.csv
This will read and add in the content of tempfile immediately after line 1.