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120 lines
3.6 KiB
Markdown
120 lines
3.6 KiB
Markdown
---
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jupytext:
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text_representation:
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extension: .md
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format_name: myst
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kernelspec:
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display_name: Bash
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language: bash
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name: bash
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---
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# Lesson 0: Exploring qsv help messages and syntax
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## Listing all commands
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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.
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```{code-cell}
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:tags: ["scroll-output"]
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qsv --list
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```
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Here we see a list of commands and a brief description about them.[^1]
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## Viewing a command's help message
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You may view a command's help message by running:
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```bash
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qsv <command> --help
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```
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For example I may run the following to get the help message for the `headers` command:
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```{code-cell}
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:tags: ["scroll-output"]
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qsv headers --help
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```
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Usually you'll find a similar structure for other qsv commands:
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- Description about the command
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- More details
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- Examples and/or a link to them
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- Usage format
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- Subcommands[^2]
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- Arguments
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- Options (flags)
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## Displaying headers of a CSV
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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:
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```{code-cell}
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qsv headers fruits.csv
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```
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## Recap
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In this lesson we've covered how to:
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- List all available qsv commands with `qsv --list`
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- View the help message for an individual command with `qsv <command> --help`
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- Interpret the parts of a command help message
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- Run a command on an arbitrary CSV file, getting the headers with `qsv headers <filepath>`
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Now it's your turn to take on the first exercise.
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## Exercise 0: Total rows
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[](https://mybinder.org/v2/gh/dathere/100.dathere.com/main?labpath=lessons%2F0%2Fexercise.ipynb)
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Using a qsv command, get the total number of rows that are in the `fruits.csv` file.
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> Here we list qsv commands for your reference. Solve this exercise using [Thebe](exercises-setup:thebe), [Binder](exercises-setup:binder) or [locally](exercises-setup:local).
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```{code-cell}
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:tags: ["scroll-output"]
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qsv --list
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```
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:::{hint}
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:class: dropdown
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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.
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:::
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::::{admonition} Solution
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:class: dropdown seealso
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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:
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```bash
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qsv count fruits.csv --no-headers
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```
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And the output should be:
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```bash
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4
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```
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:::{admonition} Why not 3?
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:class: dropdown hint
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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):
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<q>Note that the **count will not include the header row (unless `--no-headers` is given)**.</q>
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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).
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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](https://github.com/jqnatividad/qsv/discussions).
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:::
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::::
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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).
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[^2]: In this case `qsv headers` does not have any subcommands.
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