September 30, 2019

An introduction to coding: converting excel (csv) to markdown table

So you know your way around your OS (operating system) a bit, you use your terminal/CLI (command line interface) more and more and want to start coding? This post explores how you can get on your way becoming a programmer during your normal desk job.


We encourage you to use a Unix CLI more and more, on Windows I would recommend WSL, on OSx, Linux and Chromebooks it comes pre-installed.

Using the CLI changes the way you look at your directory structure and helps you get familiar with GNU tools that can be used to create scripts.

Many universities teach students to use a visual editor to create scripts and run them via the UI (e.g. Jupyter), but you will need the CLI skills when interacting with a server over SSH.

Finding problems

Software is the act of manipulating data. To find relevant use cases during our daily work, we turn to simple examples in which we want to manipulate data.

Examples are:

  • file conversions
  • file manipulations
  • data filtering/reduction

Let’s start exploring them.

Data filtering

We first show the example and then explain it:

svlentink@penguin:~$ curl --http2 -Iv 2>&1|grep -i http
* Rebuilt URL to:
* ALPN, offering http/1.1
* Using HTTP2, server supports multi-use
* Connection state changed (HTTP/2 confirmed)
* Copying HTTP/2 data in stream buffer to connection buffer after upgrade: len=0
> HEAD / HTTP/1.1
< HTTP/2 200 
* Curl_http_done: called premature == 0
HTTP/2 200 
svlentink@penguin:~$ curl --http1.1 -Iv 2>&1|grep -i http
* Rebuilt URL to:
* ALPN, offering http/1.1
* ALPN, server accepted to use http/1.1
> HEAD / HTTP/1.1
< HTTP/1.1 200 OK
* Curl_http_done: called premature == 0
HTTP/1.1 200 OK

We did two HTTP HEAD request (-I) which we inspected using verbose output (-v). This output we pipe into grep, a tool that allows us to get lines with specific keywords. We match case insensitive (-i).

File manipulation

Please run the following commands on your Unix terminal:

echo 'value=true' > /tmp/myconfig.conf
sed -i 's/value=/value=false\ #/g' /tmp/myconfig.conf
cat /tmp/myconfig.conf

We created a file, changed the boolean value and perserved the original value by making it a comment. Then we showed the output using cat. To know more about sed, just do man sed.

svlentink@penguin:~$ man sed|head -8
SED(1)                          User Commands                         SED(1)

       sed - stream editor for filtering and transforming text

       sed [OPTION]... {script-only-if-no-other-script} [input-file]...

svlentink@penguin:~$ whatis sed
sed (1)              - stream editor for filtering and transforming text
svlentink@penguin:~$ whatis cat
cat (1)              - concatenate files and print on the standard output
svlentink@penguin:~$ whatis curl
curl (1)             - transfer a URL

File conversion

We will now create our own code.

Image we have an excel sheet (data in a table), but we want to use Git as version control or simply want the table to be closer to the code. We can save the .xlsx in Git, but this wouldn’t be very practical. It’s better to have it as Markdown inside in Git so one can see the table contents in the Git webui.

Thus we want to convert the excel/sheet data into markdown table format. We first observe that we can dump a sheet in excel/google sheets as an .csv, which gives us:


We observe that Markdown uses the following format:

| A | B | C |
| --- | --- | --- |
| john | male | 21 |
| alice | female | 23 |

So we want to create this format using a script. We first see that Markdown needs a table head. So our script will look like the following:

echo '| A | B | C |'
echo '| --- | --- | --- |'

Now we need to add the lines from the .csv file and convert it to the table format. We first fiddle around and find how to convert a row:

echo 'john,male,21'|sed 's/^/|\ /g'|sed 's/,/\ |\ /g'|sed 's/$/\ |/g'
# OR
echo 'john,male,21' \
  | sed 's/^/|\ /g' \
  | sed 's/,/\ |\ /g' \
  | sed 's/$/\ |/g'

Where the first sed adds a ‘| ’ to the start of a row, the middle transforms all ‘,’ to ‘ | ’ and the last appends ‘ |’.

We now creat a script adding a shebang and a wrapper around it so you can paste it in your terminal:

cat << 'EOF' > /tmp/
echo '| A | B | C |'
echo '| --- | --- | --- |'
cat $1 \
  | sed 's/^/|\ /g' \
  | sed 's/,/\ |\ /g' \
  | sed 's/$/\ |/g'

We can now test this script:

cat << EOF | sh /tmp/

Which works very well!

We will now create a slightly updated script:

mkdir -p /usr/local/bin

cat << 'EOF' > /usr/local/bin/csv2md
#!/bin/bash -e

# check if the second argument given to the script is set
if [ -z "$2" ]; then
  echo "USAGE: $0 COLUMNCOUNT exceldump.csv >"
  exit 1

for i in $(seq 1 $1); do
  HEADER1="$HEADER1 $i |"
  HEADER2="$HEADER2 --- |"

echo $HEADER1
echo $HEADER2
cat $2 \
  | sed 's/^/|\ /g' \
  | sed 's/,/\ |\ /g' \
  | sed 's/$/\ |/g'

exit 0

chmod +x /usr/local/bin/csv2md

Which we can now test:

cat << EOF > /tmp/test.csv

csv2md 3 /tmp/test.csv

Which gives the output:

| 1 | 2 | 3 |
| --- | --- | --- |
| john | male | 21 |
| alice | female | 23 |

Or in markdown (in which I write this blog):

1 2 3
john male 21
alice female 23

Hoped you learned something today, keep searching for potential situations for creating a script and learn along the way.

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