feat: add work in progress lesson 2

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rzmk 2024-06-21 22:27:52 -04:00
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title: "Lesson 0: Exploring qsv help messages and syntax" title: "Lesson 0: Exploring qsv help messages and syntax"
- file: lessons/1/index - file: lessons/1/index
title: "Lesson 1: Displaying file content with qsv table" title: "Lesson 1: Displaying file content with qsv table"
- file: lessons/2/index
title: "Lesson 2: Piping commands"
- file: appendix - file: appendix

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fruit,price,size,availability
apple,2.50,medium,available
banana,3.00,medium,available
strawberry,1.50,small,available
orange,2.00,medium,out of stock
pineapple,3.50,large,available
grape,4.00,small,out of stock
mango,1.80,medium,available
watermelon,6.00,large,available
pear,2.20,medium,out of stock
1 fruit price size availability
2 apple 2.50 medium available
3 banana 3.00 medium available
4 strawberry 1.50 small available
5 orange 2.00 medium out of stock
6 pineapple 3.50 large available
7 grape 4.00 small out of stock
8 mango 1.80 medium available
9 watermelon 6.00 large available
10 pear 2.20 medium out of stock

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lessons/2/index.md Normal file
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---
jupytext:
text_representation:
extension: .md
format_name: myst
kernelspec:
display_name: Bash
language: bash
name: bash
---
# Lesson 2: Piping commands
:::{admonition} Lesson is a work in progress
:class: warning
This lesson is not complete. Stay tuned!
:::
We've been using one command at a time, but what if we want to use multiple?
For example let's say I want to only see what fruits there are and their availability from `fruits_extended.csv` in a nicely formatted table.
## Selecting the columns
Take a brief look at `qsv select`:
```{code-cell}
:tags: ["scroll-output"]
qsv select -h
```
There are several ways to select the columns we want. Let's take a look at the headers first:
```{code-cell}
:tags: ["scroll-output"]
qsv headers fruits_extended.csv
```
We only want data within the `fruit` and `availability` columns. Let's try selecting the data within those columns:
```{code-cell}
:tags: ["scroll-output"]
qsv select 1,4 fruits_extended.csv
```
Great, we got the column data that we're looking for. But how do we run this data through `qsv table`?
## Command redirection
If you're not sure what `stdin`, `stdout`, and `stderr` are then we recommend reading the "Command data streams (`stdin`, `stdout`, and `stderr`)" section in the Appendix.
<!-- Add link to appendix or do a dropdown or continue lesson and explain each one. -->
<!-- Improve flow for previous sentence to next one or modify flow. -->
For example let's say we want to display the previous output with `qsv table`. We can run the following to pipe the output into `qsv table`:
```{code-cell}
:tags: ["scroll-output"]
qsv select 1,4 fruits_extended.csv | qsv table
```
Now we've got what we were looking for!
:::{admonition} Exercise is a work in progress
:class: important
The exercise for this lesson is not available yet. Stay tuned!
:::