100.dathere.com/lessons/0/index.md

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Lesson 0: Exploring qsv help messages and syntax

Listing all commands

This may be your first time using qsv, so let's see what qsv has to offer. We'll run qsv with the --list flag.

:tags: ["scroll-output"]
qsv --list

Here we see a list of commands and a brief description about them.¹

Viewing a command's help message

You may view a command's help message by running:

qsv <command> --help

For example I may run the following to get the help message for the headers command:

:tags: ["scroll-output"]
qsv headers --help

Usually you'll find a similar structure for other qsv commands:

• Description about the command
• More details
• Examples and/or a link to them
• Usage format
• Subcommands²
• Arguments
• Options (flags)

Displaying headers of a CSV

Let's try viewing the headers in the fruits.csv file located in lessons/0. Based on the command format in the "Usage" section of the help message for qsv headers, we'll run:

qsv headers fruits.csv

Recap

In this lesson we've covered how to:

• List all available qsv commands with qsv --list
• View the help message for an individual command with qsv <command> --help
• Interpret the parts of a command help message
• Run a command on an arbitrary CSV file, getting the headers with qsv headers <filepath>

Now it's your turn to take on the first exercise.

Exercise 0: Total rows

Using a qsv command, get the total number of rows that are in the fruits.csv file.

Here we list qsv commands for your reference. Solve this exercise using Thebe, Binder or locally.

:tags: ["scroll-output"]
qsv --list

:::{hint} :class: dropdown

The count command may be useful for this exercise. Make sure to learn how qsv count determines the row count in order to complete this exercise as intended.

:::

::::{admonition} Solution :class: dropdown seealso

As with other solutions you may see in the upcoming exercises, there may be many ways to solve an exercise with qsv. A solution could be running the command:

qsv count fruits.csv --no-headers

And the output should be:

4

:::{admonition} Why not 3? :class: dropdown hint

The exercise requires finding the total number of rows in fruits.csv. As described in the help message for qsv count (you may run qsv count -h to get the help message):

Note that the count will not include the header row (unless --no-headers is given).

If you run qsv count fruits.csv then in your terminal you should see 3 as the output. Running it again this time with the --no-headers flag (or -n for short), you get the correct number of total rows 4 which includes the header row (which is the first row in the CSV file).

It may sound unusual that by using the --no-headers flag, the header row gets included in the row count. You may share any ideas for improvements to qsv on qsv's GitHub discussions.

:::

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1. Not all 50+ commands may be listed using qsv --list since features may be disabled for a given qsv binary file (e.g., OS compatibility for certain commands). ↩︎

2. In this case qsv headers does not have any subcommands. ↩︎