Bash is old, ugly, and quirky so why bother? It is available everywhere, it's extremely powerful and let's you complete complex tasks by combining a few lines of code. Learning Bash allows you to create scripts, specific to your use case in no time. - How do I deploy my application? - How do I setup my development environment? - How do I avoid doing this boring, repetitive task? Write a Bash script!

1. Bash:
The #1 Skill
for DevOps
Engineers
anders.janmyr@ingka.ikea.com

2. Bash:
The #1 Skill
for DevOps
Engineers

3. Ugly
and Quirky
But
Powerful and
Everywhere

4. Bash: Ugly...
Propositions
It's a script.
It's not a server.
Make it work!
Clean it up!
Move on!
Byte-sized :)
Google
Copy-Paste
Learn!
Make it work locally!
Then on CI server.

5. BAD!
Don't code in YAML!
GOOD!
Code in script.

6. first.sh

7. first.sh
Output

8. first.sh
Takeaways
# First command that reads
STDIN will wait for input.
# Every script has
STDIN, STDOUT, STDERR
Exit status
# Exit status can be used
in conditionals
# STDOUT can be captured

9. args.sh

10. args.sh

11. simple.sh
Takeaways
set -o errexit
# Exits if a command fails
"$1", "$2",...
"$@"
# Always quote args
# Every line executes a
command
'$1'
# No var expansion

12. Here docs
<<-

13. Here docs
Takeaways
"$a_var", "$(ls)"
# variable expansion
# cmd execution
$(cat <<-whatever
"Quote": "without escaping"
set -o pipefail
# Exits if a command fails
in pipe
# Great for generating
JSON

14. Caching

15. Cache
Takeaways
# Arithmetic
local sum=$(($a + 5))
if (($age > $max_age)); then
# Conditionals
if [[ -f $file ]]; then
// elif/else/fi
# -d (dir)
# Pipes
trace=$(cat $file | grep Akamai)

16. Functions

17. Functions
Takeaways
# Call
ret=my_function abc
out=$(my_function abc)
# Vars
"${file?is required}"
"${1?file is required}"
"${1:-default}"
my_function() {
local v="$1"
echo "out $v"
}

18. tag.sh

19. tag.sh
Takeaways
# Print line
before executing
[[ "$TRACE" ]] && set -x
# Trim all 'v' from left
new_version=${1##v}
# '%' from right
# Echo to stderr
echoerr() { echo "$@" 1>&2; }
# Command with if
if ! grep $version ./r.md; then
# AWK
awk "/^#.*$new_version/{flag=1;next}/^#/{flag=0}flag" $file

20. tag.sh
cont.

21. tag.sh
Takeaways
# Git multiple -m
git commit -am "Release $new_version" -m "$description"
# Git return values
if ! git diff --quiet HEAD; then
# sed
sed -i.bak -E "s/[0-9]+.[0-9]+.[0-9]+/$new_version/g" $file

22. Trap
Signals

23. Trap
Signals
cleanup() {
rm -rf $tmp_template
}
trap cleanup EXIT
# Signals
EXIT - Program Exit
SIGINT - Ctrl-C from the keyboard
SIGQUIT - Ctrl- from the keyboard

24. Useful
Commands

25. curl, jq,
tr, awk,
...

26. Watching files
Periodic
execution

27. When should
I not use
Bash?
Large Programs
> 100 Lines
Complex structures
Maps/Dicts/Structs

28. Book
Recommendation

29. Bash:
Questions
anders.janmyr@ingka.ikea.com