%title: Bash Scripting: It's not so bad
%author: Cody Hiar
%date: 2019-05-27

-> Bash Scripting: It's not so bad <-
=====================================

-------------------------------------------------

# About Me

* Graduated Computer Engineering at U of A
* SaltStack Certified
* Now working remotely @ Blendable
* Vim/Tmux Diehard, also cli in general
* Interests: Python, Automation, DevOps, Linux

# Where I be

* www.codyhiar.com
* www.github.com/thornycrackers

# Past Presentations (available on GitHub)

* Scraping with scrapy (YEGSEC)
* Python Daemons (Edmonton.py)
* Setting Django up on a VPS (Edmonton.py)
* Docker (YEGSEC)

-------------------------------------------------

-> Goals <-
===========

- What's in the Language
- Some best practices
- Resources to help

-------------------------------------------------

-> Why bash scripting? <-
=========================

- Easy win with tools you already have install.
- Scripts are easy to share between different people.
- I don't like repeating myself

^

-> When to bash script: <-
=====================

^

- Everyday. Automate everything. Invaluable for quick throw away scenarios.
  Scripting is a great way to learn how linux/unix systems in general work.

^

-> When not to bash script: <-
=========================

^

- Personal Take: If your script is getting past the 100ish line mark it's
  probably a good time to consider moving to a different language

-------------------------------------------------

-> Bash has it's own language <-
================================

Bash has support for a bunch of the basic programming features you need such as:
Variables, Functions, If/Else, Conditionals, Loops, Arrays, Dictionaries, Case
Switch.

-------------------------------------------------

# Variables

```
NAME="John"
```

# Functions

```
get_name() {
    echo "John"
}
 
echo "You are $(get_name)"
```

# If/Else

```
if [[ -z "$string" ]]; then
    echo "String is empty"
elif [[ -n "$string" ]]; then
    echo "String is not empty"
fi
```

-------------------------------------------------

# Conditionals

```
git commit && git push
git commit || echo "Commit failed"
```

# For Loop

```
for i in {1..5}; do
    echo "Welcome $i"
done
```

# While Loop

```
while true; do
  ···
done
```

-------------------------------------------------

-> The "while" poem <-
======================


While true
do foo
sleep 1
done

```
while true; do clear; curl https://duckduckgo.com; sleep 1; done
```

-------------------------------------------------

# Array

```
Fruits=('Apple' 'Banana' 'Orange')
 
echo ${Fruits[0]}  
```

# Dictionaries

```
declare -A sounds
 
sounds[dog]="bark"
 
echo "${sounds[dog]}"
```

# Case Switch

```
case "$1" in
  start | up)
    vagrant up
    ;;
 
  *)
    echo "Usage: $0 {start|stop|ssh}"
    ;;
esac
```

-------------------------------------------------

-> My First Bash Script <-
==========================

1. Run: `touch myscript.sh`
2. Add the following content

```
#!/usr/bin/env bash
echo "Hello World"
```

3. Run: `chmod +x myscript.sh`
4. Run: `./myscript.sh`

-------------------------------------------------

-> What can I put in a shell script <-
======================================

Anything you type into your terminal to run commands can be put into a bash
script. This means that Bash Scripts are essentially a free way to start
automating things that you do on a daily basis without having to install any new
tools.

-------------------------------------------------

-> Example: Postgres Backup <-
================================

```
#!/usr/bin/env bash
 
TODAY=$(date +%F)
FILENAME="database_backup-${TODAY}.sql"
 
if [[ ! -f "$FILENAME" ]]; then 
    pg_dump -h hostname -U myuser > "$FILENAME"
fi
```

-------------------------------------------------

-> Best Practice: Idempotence <-
================================

Plain English: Output or effect is the same if a script is ran multiple times.

^

This isn't limited to Bash Scripting but is a good practice in other DevOps
tools you may be using as well.

-------------------------------------------------

-> Best Practice: Unofficial Strict Mode <-
===========================================

```
#!/usr/bin/env bash
#
# Set options:
#   e: Stop script if command fails
#   u: Stop script if unset variable is referenced
#   x: Debug, print commands as they are executed
#   o pipefail:  If any command in a pipeline fails it all fails
#
# IFS: Internal Field Separator
set -euxo pipefail
IFS=$'\\n\\t'
```
-------------------------------------------------

-> Best Practice: Traps <-
==========================

```
#!/usr/bin/env bash
function finish {
  # Your cleanup code here
}
trap finish EXIT
```

Traps are the equivalent of wrapping your script in a giant `try/catch`
statement so that if anything does fail, the script will clean up after itself.

-------------------------------------------------

-> Best Practice: Linting with Shellcheck <-
============================================


The goals of ShellCheck are

    To point out and clarify typical beginner's syntax issues that cause a
    shell to give cryptic error messages.
     
    To point out and clarify typical intermediate level semantic problems that
    cause a shell to behave strangely and counter-intuitively.
     
    To point out subtle caveats, corner cases and pitfalls that may cause an
    advanced user's otherwise working script to fail under future
    circumstances.

https://github.com/koalaman/shellcheck

-------------------------------------------------

-> Best Practice: Automated testing with bats-core <-
=====================================================

Bats is a TAP-compliant testing framework for Bash. It provides a simple way to
verify that the UNIX programs you write behave as expected.

https://github.com/bats-core/bats-core

-------------------------------------------------

-> Resources <-
===============

- https://explainshell.com/
- https://misc.flogisoft.com/bash/tip_colors_and_formatting
- https://www.bash.academy/
- http://redsymbol.net/articles/bash-exit-traps/
- http://redsymbol.net/articles/unofficial-bash-strict-mode/
- https://devhints.io/bash
- https://github.com/jlevy/the-art-of-command-line
- https://google.github.io/styleguide/shell.xml
- http://www.bashoneliners.com/
- https://www.commandlinefu.com

- https://www.codyhiar.com/snippets/awesome-bookmarks-my-collection/

-------------------------------------------------

-> Questions <-
===============