---json
{
    "page_id": "hq020bdc3ffohcie057hm"
}
---
====== How to create a CSV dynamically with a script? ======


===== About =====
This ''howto'' will show you how you can create any resource dynamically with a [[:docs:resource:script|script]].

In this example, we will create a [[docs:resource:csv|CSV]] but you can create any type of resource on the fly.


===== Steps =====

==== Pre-requisites ====


You should have followed the [[script|bash script howto]] to understand how to execute and pass ''arguments'' via a [[:docs:resource:command|command]]
==== The bash script that creates the csv ====

The bash script that will be executed is:
  * a ''hello-csv'' sample [[:docs:resource:script|script]] 
  * that 
    * accepts the number of lines generated as first argument (default to 1)
    * is located in the ''command'' directory of the [[:docs:connection:howto|howto connection]]
    * outputs a [[:docs:resource:csv|CSV]]

We can print the content with the [[:docs:tabul:data:concat|data cat]] command

<unit>
<code bash>
tabul data cat command/hello-csv@howto
</code>
<console bash>
#!/usr/bin/env bash

# The first argument is the number of lines generated, default to 1
LINES=${1:-1}

# Print CSV headers
echo "Id;Greeting"

# Generate the lines
for ((i=1; i<=LINES; i++)); do
  if [ "$i" -gt 1 ]; then
    echo "$i;Hello World $i times"
    continue
  fi
  echo "$i;Hello World $i time"
done
</console>
</unit>

==== Simple execution ====

We can execute it to test that it works.

<unit>
<code bash>
tabul data print --strict-selection '(command/hello-csv@howto)@tmp'
# The quotes are only mandatory in bash because parenthesis are a bash token (ie subshell)
# We execute it with a strict-selection flag so that we get an error if the executable file is not found.
</code>
<console>
(command/hello-csv@howto)@tmp
lines
--------------------
Id;Greeting
1;Hello World 1 time
</console>
</unit>

==== Generating 3 lines ====


To pass the argument, we have created the following [[:docs:resource:command#manifest|command manifest]]

<unit>
<code bash>
tabul data cat command/hello-csv--command.yml@howto
</code>
<console yaml>
kind: command
spec:
  # the runtime data uri
  data-uri: (command/hello-csv@howto)@tmp
  # The data definition (attributes)
  data-def:
    # A list of arguments passed to the command
    arguments:
      - 3 # The first argument, the number of lines
    # Create a file with the CSV extension
    stdout-data-uri: 'execute/${execution_start_time}-${executable_logical_name}.csv@tmp'
</console>
</unit>

Executing it yield 3 lines

<unit>
<code bash>
tabul data print --strict-selection command/hello-csv--command.yml@howto
# We execute it with a strict-selection flag so that we get an error if the file is not found.
</code>
<console>
(command/hello-csv@howto)@tmp
Id;Greeting
---------------------
1;Hello World 1 time
2;Hello World 2 times
3;Hello World 3 times
</console>
</unit>


==== Defining the CSV structure ====


Unfortunately, we can see that the CSV does not split correctly the columns because the separator is a semicolon '';'' and not a the default colon '','' character.

To define the csv structure, we created the following [[:docs:resource:csv#manifest|csv manifest]]


<unit>
<code bash>
tabul data cat command/hello-csv--csv.yml@howto
</code>
<console yaml>
kind: csv
spec:
  # the command manifest
  data-uri: hello-csv--command.yml@md
  data-def:
    # the character separator
    delimiter-character: ;
    # the columns to define the data type
    columns:
      - name: Id
        type: integer
      - name: Greeting
        type: varchar
</console>
</unit>

Executing it yield now a [[:docs:resource:csv|CSV]] with 2 columns

<unit>
<code bash>
tabul data print --strict-selection command/hello-csv--csv.yml@howto
# We execute it with a strict-selection flag so that we get an error if the file is not found.
</code>
<console>
execute/20251110-204747-850-hello-csv.csv@tmp
Id   Greeting
--   -------------------
 1   Hello World 1 time
 2   Hello World 2 times
 3   Hello World 3 times
</console>
</unit>

===== Conclusion  =====

This example shows how you can create dynamic resources. 

It's the way to hack Tabulify and because it's based on programing language, the sky is your only limit.