====== Shell scripting ======

  - Download [[https://frippery.org/files/busybox/busybox.exe|busybox.exe]] from https://frippery.org/busybox/.
  - Create ''C:\opt\bin''
  - Copy busybox.exe to C:\opt\bin
  - Start busybox.exe
<code dos>
C:\opt\bin\busybox.exe sh -l
</code>

===== Merging CSV files in the current directory =====

<code bash>
# set a variable to know if a file is the first one
# because we don't want to skip the head line from the first file
first=1
# for each of *.csv file names, assign it to i
for i in *.csv; do
  # if you repeat this script, we don't want to merge
  # the previously merged file again
  if [ "$i" = "merged.csv" ]; then
    # skip this file
    continue
  fi
  # if this file is first
  if [ $first -eq 1 ]; then
    # print everything
    cat "$i"
    # subsequent files won't be first anymore
    first=0
  else
    # for non-first files, skip the first line
    tail -n +2 "$i"
  fi
done > merged.csv # forward any outputs from the above for loop
                  # to merged.csv
</code>

===== Finding the order of a column in a CSV file =====

<code bash>
head -1 merged.csv |
sed 's/"//g; s/,/ /g' |
awk '{
  for(i=1; i<=NF; i++)
    if($i == "TOBS")
      print i
}'
</code>

===== Counting non-null records in a column in a CSV file =====

<code bash>
tail -n +2 merged.csv |
sed 's/"//g; s/,/ /g' |
awk '{
  if($57 != "")
    count++
}
END{
  print count
}'
</code>